Name: Hess's Law of Heat Summation
Uploaded: 2019-07-19
Duration: 4 min 58 s
Description: What about the enthalpy changes in a chemical reaction that can take place in more than one way? Watch this video to understand this important concept of the...

Question

Use the information in Figure and the information below to demonstrate that the average bond energy of the $C - H$ bond is $415.9 kJ {mol}^{- 1}$ .

$∆ H_{f}^{°} [{CH}_{4}] = - 74.8 kJ {mol}^{- 1} . ∆ H_{at}^{°} [\frac{1}{2} H] = + 218 kJ {mol}^{- 1} . ∆ H_{at}^{°} [C (graphite)] = + 716.7 kJ {mol}^{- 1} .$

Accepted Answer

In chemistry, bond energy $(BE)$ , also called the mean bond enthalpy or average bond enthalpy is the measure of bond strength in a chemical bond.

$∆ H + ∆ H_{f}^{°} [{CH}_{4} (g)] = ∆ H_{at}^{°} [C, graphite] + 4 ∆ H_{at}^{°} [\frac{1}{2} H_{2} (g)] . ∆ H = ∆ H_{at}^{°} [C, graphite] + 4 ∆ H_{at}^{°} [\frac{1}{2} H_{2} (g)] - ∆ H_{f}^{°} [{CH}_{4} (g)] . ∆ H = (716.7 kJ {mol}^{- 1}) + [4 \times (218 kJ {mol}^{- 1})] - (- 74.8 kJ {mol}^{- 1}) . ∆ H = 1663.5 kJ {mol}^{- 1} .$

The enthalpy change for the reaction, ${CH}_{4} (g) \overset{∆ H}{\to} C (g) + 4 H (g)$ , is $1663.5 kJ {mol}^{- 1}$ . The average bone energy of the $C - H$ bond will be $\frac{1663.5}{4} = 415.87 \equiv 415.9 kJ {mol}^{- 1}$ .

Lawrie Ryan and Roger Norris Solutions for Chapter: Enthalpy Changes, Exercise 8: Question

Lawrie Ryan Chemistry Solutions for Exercise - Lawrie Ryan and Roger Norris Solutions for Chapter: Enthalpy Changes, Exercise 8: Question

Questions from Lawrie Ryan and Roger Norris Solutions for Chapter: Enthalpy Changes, Exercise 8: Question with Hints & Solutions

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