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.

34. A chemist added either Compound A or Compound B to water at 25℃. The temperature of the solution decreased until the solution began to freeze. Based on the data in Figure 1, which compound did he most likely add to the water?

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

After adding compound, the temperature of the solution drops, indicating that the solute is endothermic (ΔH is a positive number), so according to figure 1, it is known that Compound A should be added