Textbook Problem 4A.13

[Hannah Fiel 2H]

I am lost on textbook problem 4A.13. I don't understand why we found the heat capacity (in the answers) when asked to find the internal energy change. Is anyone able to explain the thought process and steps behind solving this problem?

[Chem_Mod]

In this problem since the only energy change involves the transfer of heat, the change in internal energy of the reaction is equal to heat of the reaction, q. Since the reaction takes place in a calorimeter, the heat released by the reaction is equal to the heat absorbed by the calorimeter. We can use the first known reaction to calculate the heat capacity of the calorimeter, which we then use with the temperature change of the second reaction to calculate the heat change associated with this reaction.