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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 48a
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Chapter 5, Problem 48a

Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (a) What is the enthalpy change for the reverse reaction?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy Change

Enthalpy change (ΔH) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). In the given reaction, the positive ΔH value of +630 kJ signifies that the decomposition of benzene into acetylene requires energy input.
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Reverse Reaction

The reverse reaction is simply the process of converting products back into reactants. According to the principle of conservation of energy, the enthalpy change for the reverse reaction is equal in magnitude but opposite in sign to that of the forward reaction. Therefore, if the forward reaction has a ΔH of +630 kJ, the reverse reaction will have a ΔH of -630 kJ.
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Thermodynamic Principles

Thermodynamic principles govern the relationships between heat, work, and energy in chemical reactions. These principles help predict how energy is transferred during reactions. Understanding these principles is crucial for calculating enthalpy changes and determining the feasibility of reactions under different conditions.
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Related Practice
Textbook Question

At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3: 2 KClO3(s) → 2 KCl(s) + 3 O2(g) ΔH = -89.4 kJ (c) The decomposition of KClO3 proceeds spontaneously when it is heated. Do you think that the reverse reaction, the formation of KClO3 from KCl and O2, is likely to be feasible under ordinary conditions? Explain your answer.

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Textbook Question

Consider the combustion of liquid methanol, CH3OH(l): CH3OH(l) + 3/2 O2(g) → CO2(g) + 2 H2O(l) ΔH = -726.5 kJ (a) What is the enthalpy change for the reverse reaction?

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Textbook Question

Consider the combustion of liquid methanol, CH3OH(l): CH3OH(l) + 3/2 O2(g) → CO2(g) + 2 H2O(l) ΔH = -726.5 kJ (b) Balance the forward reaction with whole-number coefficients. What is ΔH for the reaction represented by this equation?

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Textbook Question

Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (b) What is H for the formation of 1 mol of acetylene?

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Textbook Question

Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?

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Textbook Question

Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (d) If C6H6(g) were consumed instead of C6H6(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.

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