Question
A reaction is spontaneous at low temperature but non-spontaneous at high temperature.
Which of the following is true for the reaction?
A.
$$\Delta H > 0,\Delta S > 0$$
B.
$$\Delta H < 0,\Delta S > 0$$
C.
$$\Delta H > 0,\Delta S = 0$$
D.
$$\Delta H < 0,\Delta S < 0$$
Answer :
$$\Delta H < 0,\Delta S < 0$$
Solution :
We know that $$\Delta G = \Delta H - T\Delta S$$
When $$\Delta H < 0$$ and $$\Delta S < 0$$ then $$\Delta G$$ will be negative at low temperatures ( positive at high temperature ) and the reaction will be
spontaneous.