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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 14th Edition
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Tutti i libri di testoBrown 14th EditionCh.5 - ThermochemistryProblema 48a
Capitolo 5, Problema 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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Identify the forward reaction and its enthalpy change: The decomposition of liquid benzene (C6H6(l)) into gaseous acetylene (C2H2(g)) has an enthalpy change (ΔH) of +630 kJ.
Understand the concept of enthalpy change for reverse reactions: The enthalpy change for the reverse reaction is equal in magnitude but opposite in sign to the enthalpy change of the forward reaction.
Write the equation for the reverse reaction: 3 C2H2(g) → C6H6(l).
Determine the sign of ΔH for the reverse reaction: Since the forward reaction is endothermic (+630 kJ), the reverse reaction will be exothermic, which means ΔH will be negative.
Calculate the magnitude of ΔH for the reverse reaction: It will be -630 kJ, indicating that energy is released when acetylene converts back to benzene.

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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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Enthalpy of Formation

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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Reversible Changes in Matter

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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First Law of Thermodynamics
Pratica correlata
Domanda del libro di testo

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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Domanda del libro di testo

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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Domanda del libro di testo

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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Domanda del libro di testo

Consider the combustion of liquid methanol, CH3OH(l): CH3OH(l) + 3/2 O2(g) → CO2(g) + 2 H2O(l) ΔH = -726.5 kJ (d) If the reaction were written to produce H2O(g) instead of H2O(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.

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Domanda del libro di testo

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?

744
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Domanda del libro di testo

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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