Q24E - Organic Chemistry (Mcmurry)

Question

The addition of water to ethylene to yield ethanol has the following thermodynamic parameters:

 

(a) Is the reaction exothermic or endothermic?

(b) Is the reaction favorable (spontaneous) or unfavorable (nonspontaneous) at room temperature (298 K)?

Step-by-Step Solution

Answer

1. The reaction is exothermic.
2. The reaction is nonspontaneous at 298 K temperature.

Step-by-Step Solution Step 1: Exothermic and endothermic

The reaction in which heat is absorbed is called an endothermic reaction.

If $\text{ΔH}$ is positive then the reaction is endothermic.

The reaction in which heat is evolved is called an exothermic reaction.

 If  $\text{ΔH}$ is negative then the reaction is exothermic.

Step 2: Spontaneous and non-spontaneous reaction

The reaction which proceeds without the addition of external energy is called a spontaneous reaction.

The non-spontaneous reaction does not favor the product formation at any given set of conditions.

Step 3: Spontaneous reaction and entropy

Entropy is a measure of the randomness of a system.

If  $\text{ΔS}$ for the reaction is positive then the reaction is non-spontaneous.

In the above reaction value of $\text{ΔH}$ is negative then the reaction is exothermic. If the above reaction value of ${\text{K}}_{\text{eq}}$ is greater than 1 it indicates that ${\text{ΔG}}^{\text{o}}$for the reaction is positive. And if ${\text{ΔG}}^{\text{o}}$ is positive then the reaction is non-spontaneous.