Measuring the Enthalpy Change for the reaction Essay Example for Free

Measuring the Enthalpy Change for the reaction Essay Observation: 1) To start with, the copper sulphate solution is transparent blue colour. 2) At the fourth minute, using the glass rod to stir the solution as the Zinc powder is placed into the solution, the colour changes into dark turquoise and the solution fizzes due to the chemical change. 3) The Zinc powder then dissolves in the solution. 4) As I stir the solution, the colour changes to grey with black precipitate. 5) Then, the solution gradually changes from grey to black with black precipitate. At the twelfth minute, the black precipitate dissolves yet the solution continues to fizz showing the chemical reaction is still taking place. After collecting the data and recording my observations, I then draw a linear graph in order to work out the temperature rise which occurred at the fourth minute. I decided to draw my graph landscape as I figured out that drawing the graph landscape is the best method to draw the conclusion and working out the temperature rise as the data are more spread out so I can draw out a more accurate measurement. After working out the change in temperature from the graph, I will then use the value to calculate the heat given out (in Joules) during the experiment. The equation that I will be using is: q = mc ?T Hence, q = 4.18 x 28.1 x 50.0 = 5872.9 J Moles of aq copper sulphate used in the experiment: Volume x concentration = 50.0 x 0.500 = 0.0250 moles 1000 1000 Moles of Zinc power used in the experiment: Mass = 4.761 = 0.07283 mr 65.37 =0.0728(3s.f) In the method given, I was asked to weigh out the mass of the Zinc powder between 4.5g and 5g. This shows that the reagent Zinc is in excess as the mass of Zinc does not effect the outcome of the results. The limiting reagent for this experiment is copper sulphate solution. Hence, I will be using the moles of copper sulphate to work out the rest of the calculation in the experiment. I will then use the values that I have worked out from the previous calculation to work out that molar enthalpy change for the reaction: ?H = -q = -5872.9 = -234.9 Moles x 1000 0.0250 x 1000 = -235(3s.f) Note: This is assuming that the experiment is under standard condititions. During this experiment, I must also consider the errors into account as they could affect the overall results. The apparatus that I used for this experiment is the most likely cause of error for example, transferring the Zinc powder from the weighing boat to the polystyrene cup is an error as there would be Zinc powder leftover on the weighing boat but in this investigation, it would not be the case as Zinc powder is in excess so the error would not take into account. First of all, I will work out the maximum percentage error in using each piece of the apparatus. This is to ensure that I have include all the possible errors in the apparatus and so that I can comment on whether if the apparatus contributes in affecting the overall results. The maximum percentage error in apparatus: Error in balance = à ¯Ã‚ ¿Ã‚ ½0.001g = 0.001 X 100 4.761 = 0.02100 %( 4s.f) Error in the thermometer = à ¯Ã‚ ¿Ã‚ ½0.2 = 0.2 X 100 28.1 = 0.7117 %( 4s.f) Error in 50ml burette pipette= à ¯Ã‚ ¿Ã‚ ½0.05 = 0.05 X100 50.0 = 0.1% Overall maximum percentage error= 0.8327% = 0.833% (3s.f) Hence, after working out the maximum percentage error, I can use the figure to estimate the degree of uncertainty in my enthalpy change. The enthalpy change is -235 in 3s.f. I have decided to use 3s.f as an appropriate degree of accuracy so the maximum percentage error 0.8327% will be 0.833% in s.f. In my opinion, the maximum percentage error is small so therefore I dont think it will effect my enthalpy change to an extent as the smaller the number of the maximum percentage error, then the more accurate my enthalpy change will be. I also thought of including the error of the stopwatch but it wouldnt affect the maximum percentage error much so therefore I decided to exclude it from my calculation as the error is tiny and can be discarded. Conclusion The reaction between Zinc and Copper Sulphate solution is an exothermic reaction meaning that the reaction releases heat to its surrounding. Therefore, theoretically, the temperature of the solution would increase when the reaction is taking place. This is proven in my results table as when I added the Zinc powder to Copper Sulphate solution at the fourth minute, the temperature dramatically increase from 19.2à ¯Ã‚ ¿Ã‚ ½C to 40.2à ¯Ã‚ ¿Ã‚ ½C. The reaction is spontaneous as the temperature increase very rapidly and then gradually slowing down in the later time interval. From my graph, I have drawn the best fit line for the data that I plotted onto the graph to show a trend that the temperature gradually decrease after a set amount of time. The best fit line proves the accuracy of my results as the best fit line crosses most of the data that I plotted which shows that the data that I collected is reasonably reliable. The best fit line also helps me to identify the anomalies of my values as I can clearly distinguish the anomalies from my values by using the best fit line. However, I must also take into account of the two anomalies which I circled on the graph and these points do not respond to the trend of the values. This may be due to the possible errors that could have taken place during the experiment. For example, at the fifth minute after that Zinc powder has been added, the temperature that I collected (40.2à ¯Ã‚ ¿Ã‚ ½C) is an anomaly as it does not fit into the best fit line. This may be due to the fact that I havent stirred the solution properly with the glass rod so the heat may not spread through some parts of the solution so by recording the solution with the thermometer, I may receive an unreliable value so therefore I must take into account that it is important to stir the solution vigorously to ensure that the heat is spread out throughout the solution and to ensure that the precipitate has completely dissolved and no sludge remained. In order to see how well the performance of my results are, I will need to use the theoretical value of the enthalpy change and compare it with the value of my enthalpy change so that I can see how far my value is from the correct value. The theoretical values that I used are from the chemistry data book; JG Stark, H G Wallace, 1982, Chemistry data book, page 57. The values that are used for Copper aq and Zinc aq are: By using the Hess Law, I will work out the theoretical enthalpy change by using these values from the data book. = -(+64.4) + (-152.4) = -216.8 Kjmolà ¯Ã‚ ¿Ã‚ ½Ãƒ ¯Ã‚ ¿Ã‚ ½ I will then compare my value with the theoretical value of the enthalpy change. To do this, i will work out the percentage difference between my experimental value and the theoretical value. This is to see how big the percentage difference between my value and the theoretical value as the smaller the percentage, the more accurate my value will be to the theoretical value. So first, I will work out the difference between my experimental value and the theoretical value. -216.8-(-234.916) = 18.116 Kjmolà ¯Ã‚ ¿Ã‚ ½Ãƒ ¯Ã‚ ¿Ã‚ ½ Then, I will use this value to find the percentage difference between my experimental value and the theoretical value.

Gatsby :: essays research papers

The American Dream I have just read a novel called "The Great Gatsby" this novel was based in the 1920's. In this novel there are lots of drinking, and parting. In this essay I'll be writing about how the novel condemns the belief of "The American Dream", this belief states that, hard working people are successful and live happy lives. And in this novel "The American Dream" was just a mirage. One of the characters in the novel that represents the American Dream is Wilson he was one of the character that was a hard worker and own his own mechanic shop, he was one of the characters that worked every day and every night to support his family. For all he did for his family he was rewarded by his wife leaving him for another man and for a friend to have power over him with words and to get a loved one killed by a car that she was walking toward("When he came outside again a little after seven he was reminded of the conversation because he heard Mrs. Wilson's voice, load and scolding, down stairs in the garage "Beat me!" he heard her cry. "Throw me down and beat me, you dirty little coward!" A moment later she rushed out into the dusk, waving her hands and shouting; before he could move from his door the business was over. The "death car" as the newspapers called it, didn't stop; it came out of the gathering darkness, wavered tragically f or a moment and then disappeared around the next bend."Pg.144-145). For all this he got for all his hard work he went and killed Gatsby and killed himself("The chauffeur--he was one of Wolfshiem's proteges heard the shots--afterward he could only say that he hadn't thought anything much about them. I drove from the station directly to Gatsby's house and my rushing anxiously up the front steps was the first thing that alarmed anyone. But they knew then, I firmly believed. With scarcely a word said, four of us, the chauffeur, butler, gardener and I, hurried down to the pool. There was a faint, barely perceptible movement of the water as the fresh flow from one end urged its way toward the drain at the other. The touch of a compass, a thin red circle in the water. IT was after we started with toward the house that the gardener was Wilson's body a little way off in the grass, and holocaust was complete"Pg.

Community Policing Problem in the United States

Many reports from newspapers and journals claim that community policing is increasing in popularity across the United States. However there are also numerous reports that point out that community policing is not a panacea for all social ills. While community policing is in theory a very effective way of combating crime, yet in reality there are many practical problem that have to be overcome. Community policing is generally seen as a system of policing that requires optimum cooperation between the police force and the public so that the most effective methods of crime prevention and apprehension can be employed. A definition from the California Attorney General's Office is a as follows: â€Å"Community policing is a philosophy, management style, and organizational strategy that promotes pro-active problem solving and police-community partnerships to address the causes of crime and fear as well as other community issues.† In a theoretical and ideal sense community policing is, †¦ a collaborative effort between the police and the community that identifies problems of crime and disorder and involves all elements of the community in the search for solutions to these problems. It is founded on close, mutually beneficial ties between police and community members.† (About Community Policing) However there are many problems area that have to be practically dealt with in order to ensure that community policing actually lives up to these ideals. One aspect that comes to the fore when discussing this problem is that the entire concept of this form of law and order enforcement and management lies in the integration between the police and the community. One of the specific problems encountered concerns a reticence on the part of some police officers to fully participate in this symbiotic relationship. As one study puts this problem: â€Å"While community policing promises an expansion of the professional role which will be appealing to many police officers, it also requires experimentation with major changes in the way in which officers and their departments think about and organize their work.† (Riley J. 1997) The effective implementation of community policing often requires fundamental changes in the way police offers have traditionally thought about their work and the way that many police department are organized. This also implies that the strict hierarchical structure of many police departments also has to be changed to align itself with the demands of a closer cooperation with the community. All of these changes are often initially difficult to implement and an integration period is often necessary. This often necessitates that, Police departments must convince their patrol officers that it makes sense for them to take community policing seriously, if a successful transition is to take place. In this context, administrative decisions about organization, resource allocation, and the promotion of individual officers shape the understanding of patrol officers in important ways.† Adjustment problems may also take place from the point of view of the community. This is especially the case with minority communities, where prior suspicions and misunderstandings about new forms of policing may arise. However, it is mainly in the area of planning and organization, which are crucial elements in the implementation of effective community policing, that problems occur. â€Å"Problems associated with planning and coordination which characterizes the beginning of any organizational change was among the most frequently expressed concerns of the officers†¦Ã¢â‚¬  (ibid) In a study by John Riley entitled Community Policing: Perspectives from the Field, it was found that many officers felt that there was a â€Å"lack of direction† in the move towards community policing. (ibid) Another potential practical problem that has been encountered is that the policing area may be very large and therefore require more officers than would normally be the case in conventional policing activities. . â€Å"†¦ it takes a whole lot more cops to do community -presence work. Suburban counties are often big.† (Reed 2) A further aspect that has been mentioned in many reports is that if community policing does not function optimally then the blame may be directed to the police force, making the situation more difficult and complex than before. â€Å"If community policing is not able to accomplish a solution to all the communities' problems, it could easily become the scapegoat for an array of community related problems.† (Community-Oriented Policing: Blessing Or Curse?) The above are only a few of the most important issues that face community policing. While this method of law enforcement is ideal in that it optimizes the most effective relationship between the community and the police force yet, in the initial stages, it can present many practical and logistical problems. However, once these problems have been overcome, community policing often proves to be a highly effective form of law enforcement.

Major Depressive Disorder ( Unipolar Depression ) And...

The purpose of this essay is to discuss the clinical differences in the diagnosis of both Major Depressive Disorder (Unipolar depression) and Bipolar Depression can be made on the basis of characteristics of a Major Depressive Episode (MDE). That is, can an MDE in patients with Major Depressive Disorder be differentiated from a MDE in patients with Bipolar Disorder? Firstly, the extremes in mood, Major Depressive Episode and mania/hypomania will be defined and it will be explained how they contribute to a diagnosis of MDD or Bipolar Disorder based on the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders. Secondly, the importance of differentiating the two disorders based on MDE characteristics will be explained. Thirdly, the literature on the clinical characteristics of MDE in Bipolar and Unipolar Depression will be reviewed. Lastly, this essay will touch on what this means for clinicians in their decisions in diagnosing patients with Major Depress ive Disorder or Bipolar disorder. The main features of Major Depressive Episodes (MDE) include a depressed mood for most days and loss of interest and pleasure in enjoyable activities (also known as ahedonia). For the diagnoses of a MDE to be made, these symptoms must be experienced for at least two weeks and symptoms must cause significant impact on day to day functioning (APA, 2013). Additional symptoms include lack of concentration (e.g unable to focus on everyday tasks, work), lack ofShow MoreRelatedAbnormal Psychology-Unipolar and Bipolar Depression Essay1046 Words   |  5 PagesPsychology | Unipolar and Bipolar Depression | Causes, Symptoms, and Treatment | Shawn M Best 10/16/2011 | Identifying the causes of unipolar and bipolar depression can be a complicated task because there are no known exact causes, just theories. 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