Question

Estimate the enthalpy change for the combustion of one mole of methane (CH4)?

Use the following bond energies to estimate the enthalpy change for the combustion of one mole of methane (CH4). Hint: You should write a balanced equation and Lewis structures.

BondsBond Energies in kJ/mol

C-H 414 kJ/mol

O-O 142 kJ/mol

O=O 498 kJ/mol

C=O 736 kJ/mol

C-O 360 kJ/mol

O-H 464 kJ/mol

Enter the answer in kJ

Answers

A balanced equation for this process is:

CH4 + 2 O2 ---> CO2 + 2 H2O.

You are breaking:

4 C-H bonds

2 O=O bonds

and forming:

2 C=O bonds

4 H-O bonds

Enthalpy of bonds broken = 4 * 414 + 2 * 498 = 2652 kJ

Enthalpy of bonds formed = 2 * 736 + 4 * 464 = 3328 kJ

Enthalpy change = broken - formed = 2652 - 3328 = -676 kJ per mol CH4

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