Passage VI

When compounds dissolve in water, they either give off heat to, or absorb heat from, the solution. The transfer of heat (△H) is negative (exothermic) when heat is given off, or positive (endothermic) when heat is absorbed. Figure 1 shows the △H, in kilojoules per mole (kJ/mole, where 1 mole is 6 x 1023 molecules of any compound), when Compounds A or B dissolve in water at 25°C. Solubility is the maximum amount of a compound that will dissolve in a given volume of solvent. Figures 2 and 3 show how temperature affects the solubility (in moles/L) of Compounds A and B, respectively, in water.

35. Ammonium nitrate is a compound that has a △H of +25.7 kJ/mole when it dissolves in water at 25°C. Based on the data in Figure 1, if l mole each of ammonium nitrate and Compound A are dissolved separately in equal amounts of water at 25℃, how will the transfer of heat compare?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

According to figure 1, the ΔH of Compound A=+59.8 kJ/mole is higher than the ΔH of ammonium nitrate in the question, indicating that Compound A will absorb more heat, while ammonium nitrate absorbs relatively less heat