Chapter 18.5, Problem 1RC

(a)

Interpretation Introduction

Interpretation:

The circumstances in an endothermic reaction proceed spontaneously has to be identified.

Concept introduction:

Spontaneous process: A process which is initiated by itself, without the help of external energy source is called spontaneous process. All spontaneous process is associated with the decrease in free energy in the system.

Entropy: It’s is the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. Symbol for entropy is $\text{S}$ and unit is $\text{J/Kmol}$.

Entropy was also defined as the randomness or disorder of the system. Since it is thermodynamic state function it can be measured at instant, rather it was calculated as the difference in entropy of the two state, which was denoted by the symbol $\Delta \text{S}$.

Difference of exothermic and endothermic reactions:

Exothermic reaction	Endothermic reaction
Energy is given out to the surroundings	Energy is taken in from the surroundings
Enthalpy $(\Delta {\rm H})$ is negative	Enthalpy $(\Delta {\rm H})$ is positive
Products have less energy than reactants	Products have more energy than reactants

(b)

Interpretation Introduction

Interpretation:

The reason for $\text{ΔH}$ giving a good hint about the spontaneity of a reaction in which both the reactant and product species are in the solution phase has to be identified.

Concept introduction:

Entropy is a thermodynamic quantity, which is the measure of randomness in a system. The term entropy is useful in explaining the spontaneity of a process. For all spontaneous process in an isolated system there will be an increase in entropy. Entropy is represented by the letter ‘S’. It is a state function.  The change in entropy gives information about the magnitude and direction of a process. The entropy changes associated with a phase transition reaction can be found by the following equation.

  $\text{ΔS }\text{}\text{=}\text{}\text{}\frac{\text{ΔΗ}}{\text{Τ}}$

Where,

  $\Delta {\rm H}$ 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