IB Chemistry SL Reactivity 1: What drives chemical reactions? questions

Answer: D. The reaction is the system and the water is its surroundings. As the water cools, it loses energy to the reaction system. The reaction is therefore endothermic.

A: Reverses the temperature evidence; energy transferred to the water would warm it. B: Recognizes the endothermic classification but reverses the direction of energy transfer. C: Gives the transfer direction indicated by the cooling water but labels energy absorption by the system as exothermic.

Remember: cooling surroundings transfer energy to the system.

Answer: B. Enthalpy change depends on the enthalpies of the initial and final states, not on the pathway. Since those states are unchanged, $\Delta H$ is unchanged.

A: confuses the catalyst’s effect on activation energy with making the reaction enthalpy less negative.
C: assumes the alternative pathway changes the energy released, although the initial and final states are unchanged.
D: treats an alternative pathway as the reverse reaction; reversing a reaction reverses the sign of $\Delta H$

Remember: Hess’s law makes $\Delta H$ pathway-independent.