Many cold packs contain ammonium nitrate and water. The dissolving of ammonium nitrate is endothermic. Which of the following best describes the energy and entropy changes that occur for the ammonium nitrate system when ammonium and water are mixed to make a solution? A. There is a net energy increase and an entropy decrease. B. There is a net energy decrease and an entropy increase. C. There is a net energy decrease and an energy decrease. D. There is no net change in energy or entropy. E. There is a net energy increase and an entropy increase.

E. There is a net energy increase and an entropy increase.

Explanation:

A cold pack of ammonium nitrate dissolves in water with the absorption of heat energy from the surroundings. Hence it is classified as an endothermic reaction because heat is absorbed from the surroundings into the system. The absorbed energy, which increase the net heat content or enthalpy of the ammonium nitrate, causes it to dissolve.

As the ammonium nitrate changes state from solid to liquid, the degree of randomness (or entropy) increases also as the tightly bound atoms have more room to move about in a liquid state than in a solid state.

Hence as ammonium nitrate dissolves in water by absorbing heat from the surroundings, there is a net increase in heat content as well as an increase in entropy.