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.
Ch.5 - Thermochemistry
Chapter 5, Problem 47b
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?
Verified step by step guidance1
Write down the unbalanced chemical equation: CH3OH(l) + O2(g) → CO2(g) + H2O(l).
Balance the carbon atoms first. There is one carbon atom on both sides of the equation, so the CO2 coefficient is 1.
Next, balance the hydrogen atoms. There are four hydrogen atoms in CH3OH, so you need 2 water molecules (H2O) on the product side to have four hydrogen atoms.
Balance the oxygen atoms last. There are 2 oxygen atoms in CO2 and 2 more in the two H2O molecules, totaling 4 oxygen atoms in the products. Therefore, you need 2 O2 molecules on the reactant side to provide 4 oxygen atoms.
The balanced chemical equation is: CH3OH(l) + 2 O2(g) → CO2(g) + 2 H2O(l). The ΔH for the reaction remains the same, -726.5 kJ, as the stoichiometry of the reaction involving CH3OH has not changed.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Combustion Reactions
Combustion reactions are exothermic processes where a substance reacts with oxygen to produce heat and light. In the case of methanol, the reaction with oxygen produces carbon dioxide and water, releasing energy. Understanding the nature of combustion is essential for analyzing the energy changes and products formed in such reactions.
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Combustion Apparatus
Balancing Chemical Equations
Balancing chemical equations involves ensuring that the number of atoms for each element is the same on both sides of the equation. This is crucial for obeying the law of conservation of mass. In the given reaction, balancing with whole-number coefficients allows for accurate stoichiometric calculations and understanding of the reaction's proportions.
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01:32Balancing 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, meaning energy is released, as seen in the combustion of methanol. Knowing how to interpret ΔH is vital for understanding the energy dynamics of chemical reactions.
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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.
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?
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 (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.
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?
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?