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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 47a
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Chapter 5, Problem 47a

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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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 the amount of energy absorbed or released during a chemical reaction. A negative ΔH value, like -726.5 kJ in the combustion of methanol, signifies that the reaction is exothermic, releasing energy to the surroundings.
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Reverse Reaction

The reverse reaction is the process in which the products of a chemical reaction are converted back into the original reactants. For the combustion of methanol, the reverse reaction would involve converting carbon dioxide and water back into methanol and oxygen. The enthalpy change for the reverse reaction is equal in magnitude but opposite in sign to that of the forward reaction.
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Thermodynamic Principles

Thermodynamic principles govern the relationships between heat, work, and energy in chemical reactions. According to the first law of thermodynamics, energy cannot be created or destroyed, only transformed. This principle helps in understanding that the enthalpy change for a reaction and its reverse are related, allowing us to calculate the enthalpy change for the reverse reaction directly from the forward reaction's ΔH.
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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 For this reaction, calculate H for the formation of (a) 1.36 mol of O2

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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 For this reaction, calculate H for the formation of (b) 10.4 g of KCl.

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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 (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 (a) What is the enthalpy change for 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 (b) What is H for the formation of 1 mol of acetylene?

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