Question

Identify the characteristics of a spontaneous reaction.

a.) K > 1

b.) ΔG° < 0

c.) ΔE°cell > 0

d.) all of these

e) none of these

Answer 1

Answer : The correct option is, (d) all of these.

Explanation :

According to Gibb's equation:

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

$\Delta G$ = Gibbs free energy  

$\Delta H$ = enthalpy change

$\Delta S$ = entropy change  

T = temperature in Kelvin

As we know that:

$\Delta G$= +ve, reaction is non spontaneous

$\Delta G$= -ve, reaction is spontaneous

$\Delta G$= 0, reaction is in equilibrium

Relationship between standard Gibbs free energy and standard electrode potential follows:

$\Delta G^o=-nFE^o_{cell}$

For a reaction to be spontaneous, the standard electrode potential must be positive.

and,

For the reaction to be spontaneous, the Gibbs free energy of the reaction must come out to be negative.

The relation between the equilibrium constant and standard Gibbs, free energy is:

$\Delta G^o=-RT\times \ln K$

where,

$\Delta G^o$ = standard Gibbs, free energy

R = gas constant

T = temperature

K = equilibrium constant

From the above relation we conclude that,

When K > 1 then the value of $\Delta G^o$ is negative.

When K < 1 then the value of $\Delta G^o$ is positive.

When K = 1 then the value of $\Delta G^o$ is zero.

When K = 0 then the value of $\Delta G^o$ is undefined.

From this we conclude that, the option a, b and c identify the characteristics of a spontaneous reaction.

Hence, the correct option is, (d) all of these.