Question

question 8
what determines the spontaneity of a reaction?
the sign of δh.
the sign of δs_sys.
the sign of δg.
the temperature of the reaction.

Explanation:

To determine the spontaneity of a reaction, we use the Gibbs free energy change ($\Delta G$). The formula for Gibbs free energy is $\Delta G=\Delta H - T\Delta S$. A reaction is spontaneous if $\Delta G<0$, non - spontaneous if $\Delta G > 0$, and at equilibrium if $\Delta G = 0$. The sign of $\Delta H$ (enthalpy change) alone is not sufficient because a reaction with a positive $\Delta H$ can still be spontaneous if the entropy change ($\Delta S$) and temperature ($T$) are such that $T\Delta S>\Delta H$. Similarly, the sign of $\Delta S_{\text{sys}}$ (entropy change of the system) alone is not enough as a reaction with a negative $\Delta S_{\text{sys}}$ can be spontaneous at low temperatures if $\Delta H$ is negative enough. Temperature alone also does not determine spontaneity as it is just one factor in the $\Delta G$ equation. So the sign of $\Delta G$ determines the spontaneity of a reaction.

Answer:

The sign of $\Delta G$.