If a reaction has ΔH > 0 and ΔS > 0, what happens to ΔG as temperature increases?

• A. Increasing temperature makes ΔG negative; the reaction becomes spontaneous.
• B. Increasing temperature makes ΔG more positive.
• C. ΔG is independent of temperature.
• D. Spontaneity does not depend on ΔS.

Answer: (A)

The main idea is that the spontaneity of a reaction at constant pressure and temperature is governed by ΔG = ΔH − TΔS. When ΔH > 0 and ΔS > 0, the TΔS term grows as temperature increases, so ΔG gets smaller. At low temperature, ΔG may be positive, but as temperature rises, TΔS can surpass ΔH, making ΔG negative. Once ΔG becomes negative, the process is spontaneous. The temperature at which ΔG = 0 is T = ΔH/ΔS, and above that, the reaction is spontaneous.

So increasing temperature makes ΔG negative, meaning the reaction becomes spontaneous at sufficiently high temperature. The other statements ignore the TΔS term or claim independence from temperature or from ΔS, which is not correct here.