   # The standard enthalpy of formation for N 2 H 4 ( g ) is 95.4 kJ/mol. Use this and the data in Exercise 127 to estimate the N—N single bond energy. Compare this with the value in Table 3-3. ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 7, Problem 128CP
Textbook Problem
433 views

## The standard enthalpy of formation for N2H4(g) is 95.4 kJ/mol. Use this and the data in Exercise 127 to estimate the N—N single bond energy. Compare this with the value in Table 3-3.

Interpretation Introduction

Interpretation: The N-N bond energy should be calculated and comparison of the calculated and standard and values should be explained.

Hess's Law:

Standard enthalpy of formation:

• The change in enthalpy that associate with the formation of one mole of a product from its pure elements, with all substances in its standard states is called as a standard enthalpy of formation.
• Formula:

ΔHfnpΔH°f(products)-nrΔH°f(reactants)......(1)

• In equation the enthalpy change of a reaction is equal to the subtraction of standard enthalpy of formation of reactants from product.

### Explanation of Solution

Explanation

Standard enthalpies of formation of N(g) =472.7KJ/mol

Standard enthalpies of formation of H(g) =216.0KJ/mol

Standard enthalpies of formation of N2H4(g) =-46.1KJ/mol

The standard enthalpies of formation of nitrogen, hydrogen and hydrazine are recorded as shown above.

To calculate the enthalpy change ΔH of the given reaction.

Hydrazine dissociation reaction is,

N2H42N(g)+4H(g)

ΔH°=4ΔHfH(g)+2ΔHfN(g)-ΔHfN2H4(g)

ΔΗ°=2(472.7)+4(216.0)-(-95.4)=1714.0KJ

The standard enthalpies of formation values are plugging in to above equation to get the enthalpy change ΔH of given hydrazine dissociation reaction.

To calculate the N-N bond energy.

The enthalpy change of the reaction is equal to dissociation energy of three N-H bonds in hydrazine

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