Not sure Essay Example | Topics and Well Written Essays - 1250 words

Not sure - Essay Example In this activity, students were required to write about themselves on the pieces of paper and throw them to one another. This helped the students understand one another’s background and lifestyle in general. I also introduced myself to others and asked them what I wanted to know about them. This activity filled confidence in me so that I could communicate better. I learnt almost all conversation with my team members after this class rather than learning the professional words from the lecture. I learnt how important it was to be good at communication and to be able to engage with teams to get a better understanding of a new field. Since I had not done any prior readings, I did not completely understand this unit’s structure despite the fact that my unit coordinator had clearly explained everything. Besides, I was busy in few advanced professional expressions. I was eager about making a time management plan so that I was clear about the assignment submission due dates, h omework requirements and the prior reading required. It would help improve my efficiency and time management skills. Week 2 In week 2, I liked the searching activity in which I had to use the library resources together with my team members. We discovered a lot of information about our studies by accessing the online data available at the ECU website. I found out that this online library tool enabled us to locate a variety of sources. We could easily locate references of a specific year by looking at the sources for its year range. Our team did a referencing exercise including both end-text and in-text referencing following the referencing guide of ECU. We also reviewed our first pieces of reflection and exchanged views upon that with one another. For example, my team members liked my management plan’s format whereas I liked the terminology abbreviation memorizing process proposed by my mate. This activity helped improve our formatting and research skills, and also improved my ability to cooperate with my team. There was also an activity that our team did which was least interesting. It comprised two scenarios with the same set of questions about the ACE theory of Kathleen Reardon. Understanding it with real examples would have been easier than the case study in the book. Since I had done the pre-reading of the chapter â€Å"Persuasion†, I knew its importance and features already, along with the strategies needed to make effective persuasions. This part went smoothly. However, I needed to develop competence in the theoretical part of the persuasion along with their relevant terms. The learning I have gained from the online library searching activity will help me in the studies in the future and will also improve my cooperation and communication skills. I have also learnt the strategies of persuasion that I will use in my professional career in the future. Most importantly, I have developed good interpersonal skills. Week 3 Week 3 was about managem ent of stress and time. In this week, we did an activity i.e. Exercise 4B that attracted me because it was very much real; we gave a life stress test that helped us identify our stress conditions by answering different questions about our life events. I calculated my scope by ticking off many boxes of life events that were related to me and that might cause stress. I thought I would score the highest since I thought of myself as a highly stressed person, but I was surprised to learn that I had scored the lowest. I learnt that everybody experiences stress, and that

Folkloristic reflection- occupational Assignment

Folkloristic reflection- occupational - Assignment Example At the same time we also perform cowboy related activities, we make sure that your cattle herd are well taken care of by cleaning where they sleep, provide them with water and we also make sure that they are well fed. Our final responsibility is environmental cleanliness. We clean the environment and also educate the youth on the same. We realized that the current generation youth do not like taking care of the environment, therefore we took upon ourselves to educate them voluntarily (Thomas 220). Our core values and skills are respect, teamwork, good organization skills and the ability to learn. Our group has managed to accomplish a great deal because of these skills. Respect has enabled the community to trust us, at the same time we make sure that all the workers respect one another and team work has made us carry out various tasks in a short period of time. The ability to learn because the kind of work we are doing is dynamic and therefore without the willingness to learn we may not accomplish much. While good organizational skills has been emphasized by our group because we deal with a lot of activities and therefore every worker have to make sure that everything is in place. In the group the various positions are elective posts. We usually hold our elections every three months. The candidates are nominated according to their contribution to the group. Therefore, the chairman must be someone who is very hardworking and focused. Our group is very different from other groups in that whatever we do. We try to give back to the society as we make it certain that most of our activities are aimed at making sure that our society is properly maintained. In addition, we also pride ourselves in the quality of work we deliver. We make sure that all our services are done to the best of our knowledge. This can be seen by the various awards we have won and the numerous events we have been called to give a public

Principle Of Material Balance With Chemical Reaction Biology Essay

Principle Of Material Balance With Chemical Reaction Biology Essay The aim of this report is to make use of the principal of material balance with chemical reaction so to able to find out the yield, conversion rate and rate of reaction for the batch process. The hypothesis made in this experiment was when the concentration of sodium hydroxide decreases, the conductivity values also decreases. The steps for conducting this experiment are to prepare the reagents first. Then allow the reaction between the two reactants sodium hydroxide and ethyl acetate to mix together for reaction. Take note of the time and draw graphs of the reaction and finally find the yield of the reaction. There are two conditions to be studied in this case and it can be determined by the group itself. In this report, the concentration used is 0.01M of ethyl acetate and 0.02M of ethyl acetate solution. The yield calculated was that yield was higher in 0.02M of ethyl acetate compared to 0.01M of ethyl acetate. The rate of reaction is higher also in 0.02M of ethyl acetate solution based on the steepness of the graph. This is because as more molecules react with each other, more product will form at the same time and therefore in average, more product are formed at the same time and hence rate of reaction increase. However, the conductivity value was higher in 0.01M of ethyl acetate compared to 0.02M of ethyl acetate. This happened as more NaOH is being reacted with 0.02M of ethyl acetate solution. When this occurs, the conductivity value decreases as NaOH is a best conductor of electricity among the reactants and if the concentration decreases, the conductivity values also decreases and vice versa. Overall, the hypothesis made and the aim made for this experiment is correct and it also follows the law of material balance with chemical reaction. iii 1. Introduction Background Literature In the process industry, maximizing the yield is important as not only it save cost of production, but also bring more profits to a company. However, maximizing the yield is closely related to the conversion of units and rate of reaction. This is because with the help of the two factors, then maximizing yield could be done possible (Singapore Polytechnic 2009). Much time were set apart in this area at the industry to adjust the factors to optimum factors for the maximum yield it can have. Beside maximum yield, maximum reaction is also required between the reactants. Reaction rate is especially important in the industry as there is a need to know exactly what is the required time needed for the reaction to be complete. It can be calculated by finding the rate of the reaction is going at a constant time and multiply against the amount of reactants used. In this experiment, the main objective is to look at the saponification of sodium hydroxide and ethyl acetate solution to form the desired product sodium acetate. Overall, the whole experiment wanted the students to get prepared for the fundamentals of material balance with chemical reaction through the reaction between the reactants to get the final product. 1.2 Aim The aim of this experiment is to study and determine the yield, conversion and reaction rate of the starting reagents sodium hydroxide and ethyl acetate. It helps the students to know how to calculate the yield. 1.3 Hypothesis In this experiment, the main objective is to find out the relationship between the concentration of NaOH and the conductivity values. According to the theory, as the reaction of ethyl acetate increases, conductivity values will decrease and vice versa. 1 2. Theory 2.1 Introduction of Theory In this case, material balance deals with chemical reaction where students associate the product and the reactants. Material balance states that reactant that goes in to react must come out from the system as a product. The law of material balance also states that a system must, by conservation of mass, either leave the system or accumulate within the system. (Wikipedia 12 Dec 2009) The reactants used are sodium hydroxide and ethyl acetate by processing it batch wise in a reactor to produce the desired product sodium acetate and the by- product ethanol. 2.2 Saponification Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of an acid This term is normally associated with the reaction of an alkali (normally metal) with a fat compound to form soap. However, only certain lipids that contain ester linkages can undergo hydrolysis. This reaction is also catalyzed by a strong acid or base. (Wikipedia 12 Dec 2009). The alkali that is going to be used is sodium hydroxide solution and the ester that is to be used is ethyl acetate solution. After it had reacted, it will form the product sodium acetate. In the past, saponification also refers as soap making as the properties of the reactants is about the same only with the exception that fats or oil is used instead of the ester ethyl acetate. 2.3 Batch Process Batch process is an operation where a fixed amount of reactants are being fed into the reactor. It is an unsteady state process where the flow rate of the system is not proportional to the time taken to flow. So therefore, the rate where sodium acetate where it is formed is not constant and the rate of accumulation are also not constant. Accumulation consists of either the reactants which had not been used up during the reaction or the product that are being left inside the reactor. The product will stop producing if any of the reactants is used up. The reactant that is being used up first is the limiting reagent. Normally, limiting reagent is the more expensive reagent. Because it can save up cost of production as it is considered wasteful if there is any expensive reagent not used up. Ethyl acetate, being the more expensive reagent, will be the limiting reagent in wise. There are also two equations relating to the batch process. Final Output-Initial Output = Generation Consumption If there is no reaction, Initial Input= Final Output (Product=Reactants) (Singapore Polytechnic 2009) 2 2.4 Conductivity Conductivity is a measure of an electrolyte of its ability to conduct electricity. (Wikipedia 2009) The S.I unit of conductivity is Siemens per metre (S/m). Conductivity measurements are usually used in many industrial and environmental applications. This is because it has been proven as a fast, inexpensive way of measuring the ionic content of a solution. For example, the measurement of product conductivity is done so by tracing the performance of the water purification system under close monitor. In many cases, conductivity is linked directly to the total dissolved solids (T.D.S). High quality deionised water has a conductivity values of about 5.5 lS/m, drinking water is in the range of five-fifty mS/m while sea water is about 5 S/m. The reason why sea water has such high conductivity because of the ionic compounds dissolved in it and all of them are conductor of electricity. The most basic compound dissolved in seawater is table salt, Sodium Chloride. For this experiment, the result that is required is the conductivity of sodium hydroxide solution after reacting with ethyl acetate for a certain period of time. The amount of time set for the reaction is twenty minutes and it can be adjusted accordingly. 2.5 Yield Yield is the amount of product obtained in a chemical reaction. The units of yield can be given in grams or in moles. To be exact, yield is also defined as the mole/s of desired product formed per mole of key reactant fed into the reactor. This experiment also required the students to find out the yield or how much the products it has which is the desired product sodium acetate. Even though ethanol is still considered as a product, it is a by-product and hence the yield is not required to find out. 3 Procedure (Singapore Polytechnic 2009). 3.1 Pre- Assessment activity Before starting the experiment, besides preparing the starting reagents, students have to ensure what are the equipments required for this experiment. After checking it, make sure to rinsed all apparatus with D.I water to ensure no impurities present in any of the equipments. There is also a Material Safety Data Sheet (MSDS) that tell us the nature of NaOH and ethyl acetate. The data sheet also tells us what are the hazards and the safety precaution to take note of for these two compounds. 3.2 How to Prepare the Starting Reactant Firstly, students must read how to handle NaOH and ethyl acetate and the recommended way of disposing these two chemicals. Disposable gloves and chemical goggles is a must as even if the chemical spilled out, the glove will prevent the chemicals from harming the students. 500ml of ethyl acetate is to be prepared at this stage as the concentration is being discussed during the pre- assessment activity. Students may use the measuring cylinder to measure the required volume of both reactants and the volume is the pre-determined during the pre-assessment activity. Then both are being poured into the 500ml volumetric flask respectively. The solutions are to be filled up to the 500ml mark for both reactants. 3.3 Experimental Setup Pour in the NaOH solution to the reactor. Alter the set up condition accordingly by the discussed by the group earlier same as the volume used for the reactants. Make sure it is approved by the lecturer. Remember to record down the reaction of conditions such as the stirring speed of the stirrer, concentrations, temperature and the volume of the reactants. Make sure the conductivity probe is inside the solution. Pour NaOH in first. Then when ethyl acetate solution is poured in, start the timer immediately. Record the value every 1 minute and this goes on up to 20 minutes. After 20 minutes, stop the stirring device and remove the magnetic bar using the magnetic rod. Clean all the equipments properly (e.g. Clean the conductivity probe with D.I water etc). Before doing so, pour all the unwanted solution to the containers respectively. Repeat the experiment again with different condition. Repeat the steps mentioned above. Tidy up the workplace and the experiment is considered done. 4 Results And Calculation 4.1 How to Determine the Yield of Sodium Acetate at 15 Minutes for 0.01M of Ethyl Acetate? The yield of sodium acetate at 15 minutes can be determined by the concentration of NaOH. From the concentration, students can find out the amount of mole of NaOH and also by the molar ratio of NaOH and ethyl acetate. By making use of the results form the procedure, students can also find out the concentration of NaOH and ethyl acetate. Theoretical Mole of NaOH = 0.01 X 0.5L = 0.005 mol Actual Mole of NaOH = 0.00156 X 0.5L = 0.00078mol Number of moles reacted = 0.005 0.00078 = 0.00422mol Conversion of NaOH= 0.00422/0.005 X 100% = 84.4% Theoretically, since 1 mole of NaOH react and form 1 mole of CH3COONa, actual mole of CH3COONa= 0.00078 Yield of CH3COONa= 0.00078/0.005 =0.156 4.2 What Is the Yield When 0.02M of Ethyl Acetate Solution Used At 15 Minutes? Theoretical mole of NaOH = 0.02 X 0.5L = 0.01 mol Actual mole of NaOH = 0.0017 X 0.5L = 0.00085mol Number of moles reacted = 0.01 0.00085 = 0.00915mol Conversion of NaOH= 0.00915/0.01 X 100% = 91.5% Theoretically, since 1 mole of NaOH react and form 1 mole of CH3COONa, Actual mole of CH3COONa= 0.00085 Yield of CH3COONa= 0.00085/0.01 = 0.085 5 4.3 What Is the Rate of Reaction When 0.01M And 0.02M of Ethyl Acetate? Figure 1: Rate of reaction for 0.01M of ethyl acetate Figure:2 Rate of reaction for 0.02M of ethyl acetate 6 4.4 How to Determine Rate Constant The rate constant can also be determined by the graph except by drawing a tangent line against it as the tangent line mean the rate is going at a constant rate. Figure 3: Rate constant for 0.01M of ethyl acetate Graph shown above is straight line. Gradient= 0.00265-0.0012 Ã · 20 1 = 0.0000763 (From the graph) Figure 4: Rate constant of 0.02M of ethyl acetate Graph shown above is straight line. Gradient= 0.00275 0.00125 Ã · 20 1 = 0.0000789 (From the graph) 7 Discussion 5.1 Factors Affecting Rate of Constant The factor that may affect rate of constant is temperature of the reactor, concentration of the reactants, pressure or volume of the reactants. Firstly, as temperature rises, it can lead to a higher probability of particles colliding each other. Hence it will increase rate of reaction with an increase of the temperature, the moving speed of the molecules increases, with higher moving speed, it will increase the chances of molecules colliding to each other, therefore increases the rate of reaction. However, during the experiment, the temperature of the reactor was keep constant at a range of 23.5oC which is at room temperature, therefore, temperature was not taken in to account in this experiment. Secondly, concentration of the reactors, with a high concentration of the reactant, the rate of reaction with also increases. This is caused by the increasing number of particles in a reactant. With larger amount of particles, the successful rate of particles colliding in to each other are higher, therefore cater to a faster rate of reaction. However, as we are conducting the experiments, instruction of using a constant concentration of the reactant were told, therefore, concentration of the reactant is also not to be taken in to account. 5.2 Factors Affecting Conversion and Yield The equation above have NaOH and ethyl acetate as their reactants and sodium acetate and ethanol as the products formed. As indicated on the lab manual, the amount of NaOH used is fixed at 0.1M, therefore reactant A is ethyl acetate and the desired product is sodium acetate. The factors that affect the yield of the desired product are the volume and concentration of reactant A which are fed in to the reactor. With an increment of both the volume and concentration of reactant A, the number of moles of the reactant will increase. Two experiments were done to prove that volume can cater to a different yield. The first trail of the experiment, the volume of ethyl acetate was set to 0.49cm3 and on the second trial, 0.92cm3. The yield of the product decreased as the volume increased, this was proven as the yield of the second reaction was lower than the first. 8 Factors Affecting Conductivity Values Mainly, there are two main factors that are affecting the conductivity values. There are the speed of the stirrer and rate of reaction. When the speed of the stirrer increases, the conductivity values decreases. This is because it introduces more collisions between the particles and hence more products are formed at the same time. As more NaOH is being converted to sodium acetate, the conductivity value will increase as mainly NaOH is the best conductor of electricity present within the reaction and vice versa. Temperature indeed affects the conductivity values but as the temperature during the reaction is being kept constant, it will not be any of the factors that affect the reaction. Precautions In Experiment There are some precautions taken for the experiment. For example, when handle corrosive or volatile chemicals such as NaOH or ethyl acetate, make sure to wear disposable glove and avoid smelling ethyl acetate as it is a volatile liquid. Also, the smell of ethyl acetate is harmful to our body and when are diluting it, it is best to wear a surgical mask while extracting the pure ethyl acetate solution. While doing the experiment, wear safety goggles at all times to prevent the spurring of the reactants during the chemical reaction. After doing the experiment, also make sure that the magnet is taken out by the magnetic rod and not take it by the hand itself. This is because chemicals present in the beaker may not have reacted completely and traces of reactants may still be found present in the solution. This is a common mistake made by students as some of them will take it out by bare hand after realizing they did not take it out before washing. Comparison between the Yields of Different Concentration of Ethyl Acetate. Yield obtained in 0.01M of ethyl acetate is 78% while yield obtained in 0.02M of ethyl acetate is 85%. After comparing the yield between the two concentrations of ethyl acetate, 0.02M of ethyl acetate tends to have higher yield than 0.01M of ethyl acetate solution. The result is the same as the hypothesis made at the start of the report. This is because as there are more molecules of ethyl acetate present during the reaction. The rate of reaction increases because of the kinetic particle theory. The kinetic particle theory states that as more molecules collide during the reaction, it will form more products. Hence, yield will increase as more products are formed. 9 Comparison between the rates of reaction of different concentration of ethyl acetate. The curve was smoother in 0.01M of ethyl acetate compared to 0.02M of ethyl acetate. This is because with a high concentration of the reactant, the rate of reaction with also increases. This is caused by the increasing number of particles in a reactant. With larger amount of particles, the successful rate of particles colliding in to each other are higher, therefore cater to a faster rate of reaction. Hence, rate of reaction was faster in 0.02M of ethyl acetate compared to 0.01M of ethyl acetate. 10 6. Conclusion In conclusion, the aim that was made at the start of the experiment was successful as students has indeed learnt the fundamentals of material balance that even though the time required to make the product varies with the amount of products, anything that goes in must also get out is the main point that the students learnt. There are many factors that can affect the condition studied. This includes temperature, pressure, volume, rate of reaction, conversion and yield etc. Also, as the NaOH concentration increases, the conductivity values also increases and vice versa. This is the same hypothesis made in this report and therefore it can be concluded that the hypothesis is correct. 11

Analysis of We Real Cool by Gwendolyn Brooks Essay -- essays research

Poetry Essay â€Å"We Real Cool†, Gwendolyn Brooks The poem â€Å"We Real Cool† is a very powerful poem, although expressed with very few words. To me, this poem describes the bottom line of the well known â€Å"ghetto life†. It describes the desperate and what they need, other than the usual what they want, money. Without actually telling us all about the seven young men, it does tell us about them. The poem tells of the men’s fears, their ambitions, and who they think they are, versus who they really are. The poem begins with the word â€Å"We†, which is the only line in the poem that begins in this such manor, although the word â€Å"we† is repeated six more times throughout the poem. The â€Å"we† that I believe is represented at the beginning is the unity that comes from these seven friends. When y...

Is it valid to make distinctions between ‘high’ and’ low’ or ‘popular art? Essay

What purposes do these categories serve? At one time most people would have understood , when looking at apiece of art, whether to fit it into the category of high or low art. You looked at such things as the quality of the brushwork, the exactness of the representation. Then paint in tubes was invented the mid 19th century and the Impressionists were in the vanguard of almost instant art. They were rejected at first of course, but now seem to be highly acceptable when one considers the prices that might be paid for works by Renoir or Degas – however blurry the outlines. Is abstract art high art? It is a newer form of course and many are still making up their minds about such artists as Jackson Pollack. And where do you fit the works of modern artists such as Tracy Emin. Few would consider graffiti as art, but cities such as Philadelphia are legitimising the work of graffiti artists by spending public money to promote it. Emin’s unmade bed won the Turner prize. Whatever else it did it certainly did what the artist intended – it shocked. Contemporary art such as this draws huge crowds Perhaps the distinction should rather be between good and bad art, good being art that clearly displays whatever it was the artist intended and the bad that which does not. This division would not depend upon techniques used or the insurance value of a piece, but whether it achieves what it was meant to achieve i. e. whether or no the viewer sees what they were intended to see. Art will always provoke reaction. To judge it on grounds of being either ’high’ or low’ smacks somewhat of elitism – an attitude of ‘What we like is better than what you like’. Meanwhile many would just say ‘I know what I like ’ whether that be Gainsborough or Andy Warhol. Electronic Sources Art and the power to shock, Northern Echo, 25th February 2004 http://archive. thisisthenortheast. co. uk/2004/2/25/60621. html retrieved 28th October 2007 Philadelphia Mural Arts Program found at http://www. muralarts. org/about/ retrieved 28th October 2007/.

Genetic explanations Essay

Genetic explanations for the Initiation of addictions Heritability of addictions such as alcoholism and gambling can be studied through family and twin studies. The presumptions of twin and family studies are that if family members share similar behaviours, then the degree to which the behaviours are caused by genetic factors can be examined. There are two types of twins, identical and non-identical. Identical twins are monozygotic (MZ) as they came from the same egg, and therefore share an identical set of genes. Non-identical twins are dizygotic (DZ) as they come from two different eggs that were fertilised at the same time, and as a result their genes are no more alike than any brother or sister’s. Twins can also differ in the environment that they are brought up in. Some twins may, rarely, be separated at birth and therefore have very different upbringings. If researchers are able to find MZ twins who have been raised apart (i.e. same genes but different environments) then they will be able to distinguish between the influenc e of genes and environment on a certain behaviour. If MZ twins who have been raised apart booth show the same behaviour, then the behaviour is probably genetic; but if only one of them has that behaviour then it may well be caused by the environment. The degree to which twins and family members share a behaviour is termed a concordance rate, with 1 (or 100%) being entirely genetic, and 0 (or 0%) being entirely environmental. McGue (1999) found a concordance rate of 50-60% for alcohol addiction, and Agrawal & Lynskey (2006) found a concordance rate of 45-79% for addiction to illicit drugs. This means that just over half of the factors that cause addiction to alcohol are genetic in origin, as are half to three-quarters of the factors causing addiction to illegal drugs. A problem with this conclusion, however, is that the genetic link may be for behaviour disorders rather than addiction, and these behaviour disorders may manifest as many antisocial behaviours including alcohol and drug use. The sensitivity of the dopamine system is one biological explanation for the imitation, maintenance and relapse of addictive behaviours (see below), and so it would make sense for researchers to look for genes that are responsible for causing particularly sensitive or insensitive dopamine systems. One such gene is called the DRD2 gene (or dopamine receptor density 2 gene). The DRD2 gene codes for the number of dopamine receptors available in the mesolimbic dopamine system. A person with fewer dopamine receptors is  unable to ‘feel’ the effect of dopamine as well as someone with a higher number of dopamine receptors, and so needs higher levels of dopamine to produce the same effect as a person with more dopamine receptors. People with the DRD2 A1 variant of the gene have fewer dopamine receptors, and also seem more vulnerable to addictions. Evaluation for genetic explanations of addictive behaviour Genetic inheritance may explains individual differences in addiction Genetic inheritance can, through the diathesis-stress model, explain why some people become addicted whereas others in the same environmental situation do not. The diathesis-stress model is the idea that a genetic vulnerability may manifest in the right circumstance – e.g. if a person who is susceptible to becoming addicted, due to their genetic inheritance, is suffering from some form of stress or boredom due to environmental factors, then they may partake in an addictive activity. However this is a very deterministic view of human behaviour that ignores environmental factors, as not all people with the A1 variant of the DDR2 gene become addicted even if they partake in a potentially addictive activity. Inconsistent research findings linking specific genes to addictions Noble (1998) found support for the DRD2 A1 gene being linked to alcoholism (the gene was found to be carried by 48% of severe alcoholics, 32% of less severe alcoholics, and 16% of non-alcoholic controls), but many other studies have failed to find such a link. Specific genes are linked to other disorders as well as addiction The DDR2 A1 gene is also common in people with autism and Tourettes, as well as in people with addictions. Autism and Tourettes sufferers are not pleasure seekers and do not tend to suffer from addictions, and so the link between the A1 variant of the DDR2 gene and addictions is unclear and far more complex than simply claiming that the gene causes addiction. The dopamine model of addiction Initiation of addictive behaviour: Dopamine is released in the mesolimbic dopamine system of the brain, to signal reward and pleasure. If a behaviour causes dopamine release then the brain knows to â€Å"do it again† – e.g. eating, drinking, keeping warm, having sex – these are adaptive behaviours in evolutionary terms as they help an  organism/species to survive in its environment. Unfortunately other non-adaptive behaviours (i.e. behaviours that do not necessarily aid survival) can release huge amounts of dopamine (e.g. gambling and drug taking). Certain chemicals (e.g. amphetamines, alcohol, cocaine) can directly cause huge amounts of dopamine to be released. The effect of this dopamine release is to tell the brain that the behaviour is desirable and that it should seek to DO IT AGAIN! And according to incentive sensitisation theory, desire for the rewarding substance or behaviour persists even in the absence of the substance or behaviour. Maintenance of addictive behaviour: Repeated exposure to an addictive behaviour or substance causes reduced sensitivity to the dopamine release through a process known as down regulation. This means that more of the behaviour is needed to cause the same pleasurable psychological effect in the mesolimbic dopamine system. Stopping the behaviour altogether creates a state of disequilibrium in the dopamine system, and leads to withdrawal symptoms that can only be reduced by repeating the (now learned) behaviour. This disequilibrium, an increased need for dopamine stimulation, and the unpleasant withdrawal symptoms it causes now drive behaviour so that it is no longer pleasure (positive reinforcement), but the need to reduce withdrawal symptoms (negative reinforcement) that drives the addict’s behaviour. Relapse of addictive behaviour: When an addict finally manages to stop engaging in a behaviour or taking a substance, they are at risk of relapse. According to the dopamine model, relapse can be explained by addiction causing permanent brain changes that lead to lasting memories of the substance or behaviour. Environmental reminders of the addiction (e.g. being in a pub, watching horse racing, returning to a location where drugs were taken, being under stress) can release small amounts of dopamine, which in turn lead to the addicted person desiring a greater dopamine reward that can only be obtained by re-engaging in the addictive behaviour Evaluation for the dopamine model of addiction Support for the dopamine model of addiction: Support for the dopamine model comes from many experimental studies, such as  a study into the effects of ritaline (Volkow, 2001). Volkow gave a drug called ritalin to healthy volunteers and correlate their subjective experience of the drug with the density of dopamine receptors in their mesolimbic dopamine systems. Those that reported pleasurable feelings with ritalin had fewer dopamine receptors than those that hated its effects. This supports the theory that some people are more vulnerable to the effect of dopamine-releasing drugs than others. Neurochemical explanations ignore social factors: An important point to note is that neurochemical explanations for addiction (e.g. the dopamine model) ignore social and environmental factors that may also contribute to addictive behaviour. However, they can lead to effective treatments for addictions, e.g. replacing cigarettes with nicotine patches. Implications from animal research: Grant et al (1998) found that animals that lost social status also lost dopamine receptors, and offers therefore a possible explanation for social-class based addictions (e.g smoking in lower socio-economic groups). However, animal studies may not be generalisable to human addictive behaviour. Inevitability of dopamine sensitivity leading to addiction: The dopamine model suggests that reduced dopamine sensitivity, as caused by fewer dopamine receptors, inevitably leads to addictive behaviour. However, there is likely to be a complex interaction between an individual’s specific environment and whether or not dopamine sensitivity leads to addiction. A stimulating environment may provide enough dopamine reward to protect people from addiction, whereas a dull or boring environment may not (Volkow, 2003). Neurochemical explanations are reductionist: Neurochemical explanations for addiction reduce addictive behaviour to a simple variance in the structure of the dopamine system, and so ignore social and cognitive factors that can influence addictions. However they can lead to effective treatments, so in this case it is useful to be reductionist.