Question

In a chemistry lab-Calorimetry and heat of reaction we used coffee cups and thermometers to measure the heat of reactions of 3 different solutions (also using Hess' Law)

1. KCl + H2O

2. NaOH+HCl

3. Acetic acid + NaOH

in all three calculations for q=mc(delta)T, we assumed that the final solutios all had the same density and heat capsity as pure water and in the post lab it asks:

Comment on the validity of asuming that the final solutions in all three reactions had the same specific heat and density as pure water. Be sure to consider the complete composition of the solutions you start with and what you end up with.

I have no idea why we just assumed they had the same specific heat and density of water... why can we do that?

Answer 1

Solution :-

For the given three reactions the amount of heat absorbed or produced by the reaction is determined by performing the experiment in the coffee cup calorimeter

All the reactions are carried out in the water so the when the reaction produces the heat or absorbs the heat then it causes the change in the temperature of the water solution.

Therefore to determine the amount of heat absorbed or given by the reaction we need to assume that the when the reactions are complete then the final solution has same density and specific heat as water. Because we do not know the exact specific of the different solutions so we assumed it as same as water. Also the density of the solution is assumed same as water so we can directly use the volume of solution as the mass of solution because density of the water is 1 g per ml so the volume of solution is nothing but considered as mass of solution.