Chapter 18, Problem 87SCQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Decide whether each of the following statements is true or false. If false, rewrite it to make it true. (a) The entropy of a substance increases on going from the liquid to the vapor state at any temperature. (b) An exothermic reaction will always be spontaneous. (c) Reactions with a positive ΔrH° and a positive ΔrS° can never be product-favored. (d) If ΔrG° for a reaction is negative, the reaction will have an equilibrium constant greater than 1.

Interpretation Introduction

Interpretation:

It should be determined whether the given statements are true or false.

Concept introduction:

Spontaneous reactions are referred to those that have negative free energy formation. The spontaneous reactions favors the product formation. The expression is,

ΔrGorHo-TΔrSo

The value of ΔrGo should be negative.

The reactions can be classified as exothermic reactions and endothermic reactions. Exothermic reactions are those in which heat is liberated and have negative enthalpy change whereas the endothermic reactions are those in which heat is absorbed.

Explanation

Reasons for the correct statements

Entropy increases in the order solid < liquid < gas.  In the gaseous state, the particles are more random. In solids, the particles have fixed positions and entropy is less. In liquids, there are constraints due to forces between the particles. Thus, the given statement (a) is true.

If ΔrGo for a reaction is negative, the reaction will have equilibrium constant greater than 1. The ΔrGo is related to the equilibrium constant Kp by the equation,

ΔrGo= -RTlnKp

The rearranged expression is,

Kp= e-ΔrGoRT

Thus, if the sign of ΔrGo is negative, the magnitude of Kp will be greater than 1. Thus, the given statement (d) is true.

Reason for the incorrect statements

An exothermic reaction is not necessary to be always spontaneous. The spontaneity of any reaction is decided by the sign of ΔGo

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