The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C.As ammonium nitrate dissolves,the temperature of the water decreases.What are the signs of Δ_rH,Δ_rS,and Δ_rG for this process? A) Δ_rH 0,Δ_rS 0 B) Δ_rH 0,Δ_rS 0,and Δ_rG 0 C) Δ_rH 0,Δ_rS 0,and Δ_rG

Question

The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C.As ammonium nitrate dissolves,the temperature of the water decreases.What are the signs of Δ_rH,Δ_rS,and Δ_rG for this process? A) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0 B) Δ_rH > 0,Δ_rS > 0,and Δ_rG > 0 C) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0 D) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0 E) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0

Quizplus · Accepted Answer

The dissolution of ammonium nitrate in water is an exothermic process (it releases heat), so Δ_rH is expected to be positive. As the temperature of the water decreases during the process, this implies that the entropy of the system (ammonium nitrate and water) decreases as well, hence Δ_rS should also be positive. Finally, since the reaction is spontaneous (it occurs without the need of external work), it follows that the Gibbs free energy of the system (Δ_rG) is negative. Therefore, the best choice is C, with Δ_rH > 0, Δ_rS > 0, and Δ_rG < 0.

The Dissolution of Ammonium Nitrate Occurs Spontaneously in Water at 25