Question

A change in the free energy of a system at constant temperature and pressure will be:
${\Delta }_{sys}G={\Delta }_{sys}H-T{\Delta }_{sys}S$

At constant temperature and pressure
${\Delta }_{sys}G<0\left(spontaneous\right)$
${\Delta }_{sys}G=0\left(equilibrium\right)$
${\Delta }_{sys}G>0(non-spontaneous)$

The free energy for a reaction having $\Delta H=31400cal$, $\Delta S=32cal{K}^{-1}mo{l}^{-1}$ at ${1000}^{\circ }C$ is?

• A. $-9336cal$
• B. $-7006cal$
• C. $-2936cal$
• D. $+9006cal$

Answer 1

Answer: (A)

$-9336cal$

Change in the free energy of a system at constant temperature and pressure will be:

${\Delta }_{sys}G={\Delta }_{sys}H-T{\Delta }_{sys}S$

As we know,

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

$\Delta G=31400-1273\times 32=-9336cal$