Chapter 18, Problem 18.45QP

Interpretation Introduction

Interpretation:

A spontaneous process giving negative change in entropy has to be explained by using example of the freezing of water.

Concept Introduction:

In thermodynamics a process is spontaneous if it is taking place by itself without the help of external energy.  Free energy (Gibbs free energy) is the term that is used to explain the total energy content in a thermodynamic system that can be converted into work.  The free energy is represented by the letter G.  All spontaneous process will have highly energetic initial state than the final state.  This indicates that while the process occurs, there is a decrease in free energy of the system.  The increase in randomness also favors the spontaneity of a process.  In nonspontaneous process, there is a requirement of external energy source.  The free energy of the system increases.  The entropy decreases in non-spontaneous process.

The equation given below helps us to calculate the change in free energy in a system.

  $\text{ΔG = }\Delta {\rm H}\text{- T}\Delta \text{S}$

Where,

  $\text{ΔG }$ is the change in free energy of the system.

  $\Delta {\rm H}$ is the change in enthalpy of the system.

  $\text{T}$ is the absolute value of the temperature.

  $\Delta \text{S}$ is the change in entropy in the system.