What assumptions are made in calorimetry experiments? Thank you, its for Chemistry (Water) :)

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mvcdc | Student, Graduate | (Level 2) Associate Educator

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Calorimetry is the study of heat transfer during physical and chemical processes (e.g. dissolution of salt, or reaction of hydrogen and oxygen). In these kinds of experiments, the heat of chemical reactions are measured. These can be performed using calorimeters. 

A practical and common set-up for a calorimeter involves a constant-volume container called the 'bomb' in which the reaction is to take place. The bomb is then immersed into a stirred water bath. This is already your calorimeter. The entire calorimeter is then placed in another external water bath. Then, the temperature of the water (internal and external) are monitored and kept at the same temperature. This brings us to the first assumption:

  1. No heat is lost to the environment - that is, energy exchange only happens between the object of interest and water. No heat is lost to the surroundings.
  2. In connection to Assumption 1, there is only a very negligible (if any) transfer of energy to the walls of the container (this is the energy transferred to the calorimeter itself, which is still part of the system. This assumption is necessary because measurements are made to water -- see Assumption 1).
  3. The heat measured is then attributed to a complete reaction. Hence, it is always assumed that the reaction is 100% complete - i.e. 100% Yield, which never happens in real life.
  4. For dilute solutions, the assumption is that the density is always equal to that of water (1.00 g/ml) with a specific heat capacity of 4.18 joule per gram per degree Celcius.
  5. In connection to Assumption 3, it is also assumed that in whatever chemical reaction is being studied, no side reaction is occuring, and that no impurity is present in the system (which is of course a necessity, and the experimenter should make sure that there is as little impurity as possible).
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