Chemistry
Chemistry
10th Edition
ISBN: 9781305957404
Author: Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher: Cengage Learning
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Chapter 6, Problem 79E

The bombardier beetle uses an explosive discharge as a defensive measure. The chemical reaction involved is the oxidation of hydroquinone by hydrogen peroxide to produce quinone and water:

C6H4(OH)2(aq) + H2O2(aq) → C6H4O2(aq) + 2H2O(l)

Calculate ΔH for this reaction from the following data:

C6H4(OH)2(aq) → C6H4O2(aq) + H2(g)    ΔH = 177.4 kJ

H2(g) + O2(g) → H2O2(aq)    ΔH = −191.2 kJ

H2(g) + 1 2 O2(g) → H2O(g)    ΔH = −241.8 kJ

H2O(g) → H2O(l)    ΔH = −43.8 kJ

Expert Solution & Answer
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Interpretation Introduction

Interpretation:

The ΔH value for the given reaction should be calculated.

Concept Introduction:

Enthalpy change: It is defined as the amount of heat released or absorbed by the chemical reaction at constant pressure conditions.

Specific heat capacity: It is the amount of heat required by the substance to increase temperature of the 1 kilogram of the substance by 1 kelvin.

Calorimeter: It is the device used to measure the heat involved in the chemical reaction.

The heat released by the reaction is measured in calorimetry by using the following formula.

Coffee cup calorimeter: It is used to measure the heat in the reaction where the atmospheric pressure remains constant. It is also regarded as constant pressure calorimeter.

Bomb calorimeter: It is used to measure the heat which the volume kept constant. Hence it enables us to find the energy changes in the reaction. It is also regarded as constant volume calorimeter.

Answer to Problem 79E

The ΔH value for the given reaction is -202.6kJ.

To calculate: The ΔH value for the given reaction.

Explanation of Solution

Examining the given process the enthalpy change value that is ΔH for the given reaction calculated as follows,

Given,

C6H4(OH)2(aq)C6H4O2(aq)+H2(g)ΔH = 177.4kJH2(g)+O2(g)H2O2(aq)ΔH = -191.2kJH2(g)+12O2(g)H2O(g)ΔH = -241.8kJH2O(g)H2O(l)ΔH = - 43.8kJ

The final given reaction is obtained by equating all the four given reactions where second reaction is written in reverse order hence its ΔH value will be then positive value.

Then third and fourth reactions are multiplied by 2 which their ΔH values should also be multiplied by 2.

Hence, the final reaction C6H4(OH)2(aq)+H2O2(aq)C6H4O2(aq)+2H2O(l) is obtained by rearranging the given set of equations as follows,

C6H4(OH)2(aq)C6H4O2(aq)+H2(g)ΔH = 177.4kJH2O2(aq)H2(g)+O2(g)ΔH = 191.2kJ2H2(g)+O2(g)2H2O(g)ΔH = 2×-241.8kJ2H2O(g)2H2O(l)ΔH = 2×- 43.8kJ   ------------------------------------------------------------------------------------                  C6H4(OH)2(aq)+H2O2(aq)C6H4O2(aq)+2H2O(l)

Now, addition of ΔH values for the four set of arranged reactions will results to give -202.6kJ.

Therefore, the ΔH value for the given reaction is -202.6kJ.

Conclusion

The ΔH value for the given reaction was determined.

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Chapter 6 Solutions

Chemistry

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