Question

At what temperature will the following reaction happen spontaneously, given that ΔH=8.91×103J and ΔS= –219.20 J/K? CaSO4(s) + 2HCl(g) → CaCl2(s) + H2SO4(l)
A) at 298 K
B) at 100 K
C) It is spontaneous at any temperature.
D) It is not spontaneous at any temperature.

Answer 1

Answer:

D) It is not spontaneous at any temperature.

Explanation:

Given reaction:

CaSO4(s) + 2HCl(g) → CaCl2(s) + H2SO4(l)

ΔH = +8.91*10³ J

ΔS = -219.20 J/K

The sign of the Gibbs free energy (ΔG) determines the spontaneity of a given reaction. ΔG is related to ΔH and ΔS as follows:

$\Delta G = \Delta H-T\Delta S$

A reaction is spontaneous only when ΔG is negative i.e. ΔG < 0

Under the given conditions:

ΔH > 0 ; ΔS <0 and ΔH > ΔS

i.e. ΔG = ('+' value) - T( '- 'value) = + value

Therefore, irrespective of the temperature, ΔG will always be positive

Answer 2

DG = DH - TDS 

For this reaction DH>0 and DS<0. So, d. the reaction is not spontaneous at any temperature.