Chapter 18, Problem 49PS

### 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

# For the synthesis of ammonia from its elements at 25 °C,N2(g) + 3 H2(g) → 2 NH3(g) (a) Calculate ΔrG° using values of ΔfG°. Is the reaction product-favored at equilibrium? (b) Calculate ΔrG when the reactants and product are each present at a partial pressure of 0.10 atm. Is the reaction spontaneous under these conditions?

(a)

Interpretation Introduction

Interpretation:

The ΔrG° for the given reaction should be calculated using ΔfG° values and identified that reaction is product favoured at equilibrium.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrG°. It can be calculated in a similar manner as entropy and enthalpy. The expression for the free energy change is:

ΔrG°fG°(products)fG°(reactants)

ΔrG° is related to the reaction quotient Q by the expression,

ΔrG = ΔrG°+ RT lnQ

For a general reaction, aA + bB cC + dD

Q = [C]c[D]d[A]a[B]b

Explanation

The ΔrGo for the given reaction is calculated below.

Given:

The Appendix L referred for the values of standard free energy values.

The given reaction is,

N2(g)+3H2(g)2NH3(g)

The ΔfG° value for NH3(g) is 16.37 kJ/mol.

The ΔfG° value for H2(g) is 0 kJ/mol.

The ΔfG° value for N2(g) is 0 kJ/mol.

ΔrG°fG°(products)fG°(reactants)[(2 mol NH3(g)/mol-rxn)ΔfG°[

(b)

Interpretation Introduction

Interpretation:

The ΔrG° for the given reaction should be calculated when both reactants and product are present at partial pressure of 0.10atm and should be identified that the reaction is spontaneous under such conditions.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrG°. It can be calculated in a similar manner as entropy and enthalpy. The expression for the free energy change is:

ΔrG°fG°(products)fG°(reactants)

ΔrG° is related to the reaction quotient Q by the expression,

ΔrG = ΔrG°+ RT lnQ

For a general reaction, aA + bB cC + dD

Q = [C]c[D]d[A]a[B]b

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