Q. 12 P - Organic Chemistry (Mcmurry)

Question

Which reaction is faster, one with ${\mathbf{\Delta G}}^{\mathbf{\#}}$= +45 or one with ${\mathbf{\Delta G}}^{\mathbf{\#}}$= +70?

Step-by-Step Solution

Answer

The reaction with ${\mathbf{\Delta G}}^{\mathbf{\#}}$= + 45is a faster reaction.

Step 1: Spontaneous reaction

Reactions that proceed without an external energy supply are called a spontaneous reaction.

For a reaction to be spontaneous, it needs to have a negative value of Gibbs free energy.

Also, for the reaction to be spontaneous, the value of ${\mathrm{\Delta S}}^{°}$ needs to be positive

Step 2: Rate of reaction and ΔG # value

A fast reaction has a small ${\mathrm{\Delta G}}^{\#}$ value. It means that smaller the value of ${\mathrm{\Delta G}}^{\#}$ the rate of reaction is higher.  

In the above case, there are two values for ${\mathrm{\Delta G}}^{\#}$—one is +45 and the second one is +70. Out of which +45 is thesmaller value so the reaction with ${\mathrm{\Delta G}}^{\#}$= +45 is thefaster reaction.