Question

Suppose that a reaction has $\Delta H=40kJ$ and $\Delta S=50kJ/K$. At what temperature range will it change from spontaneous to non-spontaneous?

• A. $0.8K$ to $1K$
• B. $799K$ to $800K$
• C. $800K$ to $801K$
• D. $799K$ to $801K$

Answer 1

The correct option is A $0.8K$ to $1K$

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

$\Delta H=$40 kJ

$\Delta S=$50 kJ/K

if $\Delta G$<0, process is spontaneous

if $\Delta G$>0, process is non spontaneous

if $\Delta G$=0, process is in equilibrium

For T$=0.8$K

$\Delta G=40-0.8\times 50=0$

$\Delta G$=0

The process is in equilibrium

For T$=1$K

$\Delta G=40-1\times 50=-10$

The process is in spontaneous