Question

Chemistry Calorimetry experiment questions
1. Why is dissolving of ammonium chloride endothermic? would you get similar results for dissolving all salts? explain your answer using another salt as an example.
2. Suppose the calorimeter used for this experiment had been made of a heat-conducting material (such as metal) rather than styrofoam. Would the measured calorimeter constant be larger or smaller. Explain your answer.
3. Why do you use the heat capacity of 2.5M NaCl solution rather than the heat capacities of the original acid and base solutions?

Answer 1

1. Why is dissolving of ammonium chloride endothermic? would you get similar results for dissolving all salts? explain your answer using another salt as an example.

Lattice Energy is the energy required to pull the ions apart from each other, and Hydration Energy is the energy released into the solution when the ions are surrounded by water molecules. Whether the dissolution of salt is endothermic or exothermic depends on the extent of Lattice Energy and Hydration Energy. Dissolution of salt will become endothermic when the lattice energy of the salt becomes higher than the hydration energy of the salt. Thus, dissolution of ammonium chloride is endothermic because lattice energy of ammonium chloride is higher than the hydration energy. Dissolution of all salts need not be endothermic. For salt such as NaCl, Lattice Energy is 779 kJ/mol, and Hydration Energy is 774 kJ/mol, and the dissolution is exothermic.

2. Suppose the calorimeter used for this experiment had been made of a heat-conducting material (such as metal) rather than styrofoam. Would the measured calorimeter constant be larger or smaller? Explain your answer.

If instead of Styrofoam, the calorimeter was made from metal, then the measured calorimeter constant would be smaller. Because heat conducting materials such as metals will have a small specific heat capacity and are sensitive to temperature changes, and much of the heat will be transferred to the metal rather than staying in the solution

3. Why do you use the heat capacity of 2.5M NaCl solution rather than the heat capacities of the original acid and base solutions?

Instead of the heat capacities of NaOH and HCl, the heat capacity of the NaCl solution is used. Because, in aqueous solution, NaOH and HCl will dissociate completely and form NaCl. Therefore, the heat capacity of 2.5M NaCl solution rather than the heat capacities of the original acid and base solutions are used.