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Investigation into the factors that affect the enthalpy change during a displacement reaction.

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Introduction

Investigation into the Factors that Affect the Enthalpy Change During a Displacement Reaction. The Task To investigate the factors affecting the enthalpy change during a displacement reaction. Background Knowledge In this investigation a displacement reaction will be observed. A displacement reaction occurs when more reactive metal displaces, (or removes) a less reactive metal from a solution of its salt. Also known as chemical bullying because a more reactive metal effectively bullies the original metal out of its compound. In this investigation zinc and copper sulphate will be reacted together. Zinc is the more reactive metal here, so the copper is displaced from the copper sulphate solution. Zinc + Copper sulphate --> Zinc sulphate + Copper Zn (s) + CuSO4 (aq) --> ZnSO4 (aq) + Cu (s) After the reaction it will be observed that the solution will change from blue to clear, colourless. The copper discharged will be observed as a salmon pink deposit in the base of the vessel the reaction occurs in. Reactions like this can be used to purify metals that are low down in the reactivity series. A more reactive metal can simply be added to purify the less reactive metal, leaving it in its pure state. Lead Oxide + Tin --> Lead + Tin Oxide In reality thought this process is hardly ever used, as the more reactive metal is the left in an impure form, and thus must be reduced by an even more reactive metal. ...read more.

Middle

It is important to maintain a fair test while investigating a variable. This means that when one variable is changed all the others must remain constant. This ensures that results achieved are due to a specific variable, and not due to another that is also being altered. e.g. when concentration is changed, mass and surface area must remain constant, thus ensuring that accurate results are achieved, so a precise conclusion can be achieved. Range and Number of Observations It is important that all experiments undergone are repeated a minimum of 2 times so that a men average can be taken from the results. Ideally each experiment should be repeated about 5 times, thus helping to account for anomalies. It is also important that sufficient ranges of results are taken. For example I believe it is important to measure the temperature of the solution at intervals of every 10 seconds. This will help to show the precise cooling curve and should make extrapolations on a graph more accurate. Each variable investigated should be tested at about 5 different values, so when concentration is tested at least 5 different concentrations should be used, e.g. 1.0, 0.5, 0.25, 0.125, 0.05125. Accuracy of Observations To achieve accurate results I will perform each experiment a minimum of 3 times. This will mean that I can take an average, thus helping to account for anomalies. ...read more.

Conclusion

All experiments should be repeated a minimum of 3 times so that a mean average of the findings can be taken. All results should then be tabulated and formatted on a graph to help explain a trend in the relationship between mass of zinc and enthalpy change in the reaction. A conclusion should then be reached. Calculations Using the extrapolations on the graph showing the relationship between time and temperature the energy change evolved in each reaction can be calculated. The can be worked out by using the equation: q = mc/\T When, q = heat energy (in J), m = mass of copper sulphate solution (assuming density is equal to 1g/cm3), c = specific heat capacity of the solution (assume this equals 4.2 J/g/degrees Celsius), /\T = temperature change (estimated from extrapolation). The results here show the heat energy in each reaction. To calculate the enthalpy change one must account for the respective moles involved in each reaction. To equal out the number of moles simply multiply the results by the respective amounts required to make them all amounts of Joules/1 mole. When this calculation is performed on all the heat energy results enthalpy change can be compared. In an accurate experiment the enthalpy change when copper sulphate solution is reacted with zinc powder should remain constant. By taking into account the number of moles in each equation when multiplying the results will be brought into proportion, so the enthalpy changes should be roughly equal. Stephen Foulks ...read more.

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