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Hess’ Law Practical Background: There are many reactions for which direct measurement of the enthalpy reaction is difficult, the hydration of magnesium sulfate being such a reaction. In these cases it is often possible to determine the enthalpy of reaction by direct measurements on more accessible related systems and then applying Hess’ Law. Aim: to determine the change in enthalpy for the hydration of magnesium sulfate using Hess’ Law. Hypothesis: It looks like there are being more bonds formed than broken in this reaction, therefore, I think the change in enthalpy will be exothermic. Variables: - Temperature of the surroundings (this should not effect our experiment because it will be carried out in a polystyrene cup). - Air pressure (will have no effect on our experiment as it should not change during the short time our experiment will take.) - Temperature of the water (there will be an error with the thermometer) - Mass of MgSO4 and MgSO4•7H2O (error on the electronic balance) - Specific Heat Capacity (we are using the specific heat capacity of water) - Volume of Water – this is the controlled variable, as we will use the same amount of water in each experiment. - Water may have impuriti