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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 15th Edition
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Tutti i libri di testoBrown 15th EditionCh.5 - ThermochemistryProblema 47b
Capitolo 5, Problema 47b

Consider the combustion of isopropanol, C3H7OH(l), which is the primary component of rubbing alcohol: C3H7OH(l) + 9/2 O2(g) → 3 CO2(g) + 4 H2O(l) ΔH = -2248 kJ (b) Balance the forward reaction with whole-number coefficients. What is ΔH for the reaction represented by this equation?

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Identify the given unbalanced chemical equation: \( \text{C}_3\text{H}_7\text{OH}(l) + \frac{9}{2} \text{O}_2(g) \rightarrow 3 \text{CO}_2(g) + 4 \text{H}_2\text{O}(l) \).
To balance the equation with whole-number coefficients, multiply all coefficients by 2 to eliminate the fraction: \( 2 \text{C}_3\text{H}_7\text{OH}(l) + 9 \text{O}_2(g) \rightarrow 6 \text{CO}_2(g) + 8 \text{H}_2\text{O}(l) \).
Verify that the number of atoms of each element is the same on both sides of the equation: 6 C, 16 H, and 18 O on both sides.
Since the coefficients of the balanced equation are doubled, the enthalpy change \( \Delta H \) for the reaction must also be doubled. Calculate the new \( \Delta H \) by multiplying the given \( \Delta H = -2248 \text{ kJ} \) by 2.
The new \( \Delta H \) represents the enthalpy change for the balanced reaction with whole-number coefficients.

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Combustion Reactions

Combustion reactions involve the reaction of a substance with oxygen, producing heat and light. In organic compounds, such as isopropanol, combustion typically yields carbon dioxide and water. Understanding the stoichiometry of combustion is essential for balancing the reaction and calculating energy changes.
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Combustion Apparatus

Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation. This is crucial for accurately representing the conservation of mass during a chemical reaction. Whole-number coefficients are used to achieve this balance, which is necessary for stoichiometric calculations.
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Balancing Chemical Equations

Enthalpy Change (ΔH)

Enthalpy change (ΔH) represents the heat absorbed or released during a chemical reaction at constant pressure. A negative ΔH indicates an exothermic reaction, where heat is released, as seen in combustion. Understanding ΔH is vital for evaluating the energy efficiency of reactions and predicting the feasibility of chemical processes.
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Enthalpy of Formation
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