Question

Condition for reaction to be spontaneous at constant temperature and pressure ​

Answer 1

i hope u know the formula for gibss free energy.A reaction is spontaneous ONLY when value of gibss free energy is negative. If for a chemical reaction delH is negative and delS is positives then the gibss free energy will always be negative and hence the reaction will be always spontaneous.

Answer 2

Gibb's free energy should be negative for a reaction to be spontaneous.

At constant Pressure and Temperature, we have the relation

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

Therefore for G to be negative, the term $\Delta H - T\Delta S$ must be negative.

• For exothermic reactions, the reaction will be spontaneous at all temperatures if entropy change is positive, and at low temperatures if entropy change is negative.
• For endothermic reactions, the reaction will be spontaneous at high temperatures if entropy change is positive, and at no temperature if entropy change is negative.

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