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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 39a
Chapter 5, Problem 39a

The complete combustion of methane, CH4(g), to form H2O(l) and CO2(g) at constant pressure releases 890 kJ of heat per mole of CH4. (a) Write a balanced thermochemical equation for this reaction.

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Identify the reactants and products in the combustion of methane. Methane (CH4) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
Write the unbalanced chemical equation for the combustion of methane: CH4(g) + O2(g) -> CO2(g) + H2O(l).
Balance the chemical equation. Start by balancing the carbon atoms: CH4(g) + O2(g) -> CO2(g) + H2O(l). Since there is one carbon atom in CH4 and one in CO2, the carbon is already balanced.
Next, balance the hydrogen atoms. There are 4 hydrogen atoms in CH4, so you need 2 H2O molecules to balance the hydrogen: CH4(g) + O2(g) -> CO2(g) + 2 H2O(l).
Finally, balance the oxygen atoms. There are 2 oxygen atoms in CO2 and 2 in 2 H2O, totaling 4 oxygen atoms needed. Therefore, you need 2 O2 molecules: CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(l). Include the enthalpy change: CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(l) ΔH = -890 kJ/mol.

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Related Practice
Open Question
Assume that 2 moles of water are formed according to the following reaction at constant pressure (101.3 kPa) and constant temperature (298 K): 2 H2(g) + O2(g) → 2 H2O(l). (b) Calculate _x001F_E for the reaction using your answer to (a).
Open Question
Suppose that the gas-phase reaction 2 NO(g) + O2(g) → 2 NO2(g) were carried out in a constant-volume container at constant temperature. (a) Would the measured heat change represent _x001F_H or _x001F_E? (b) If there is a difference, which quantity is larger for this reaction? (c) Explain your answer to part (b).
Textbook Question

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is added to the gas, it expands and does 214 J of work on the surroundings. What are the values of H and E for this process?

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Textbook Question

The complete combustion of methane, CH4(g), to form H2O(l) and CO2(g) at constant pressure releases 890 kJ of heat per mole of CH4. (b) Draw an enthalpy diagram for the reaction.

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Textbook Question

The decomposition of sodium bicarbonate (baking soda), NaHCO3(s), into Na2CO3(s), H2O(l), and CO2(g) at constant pressure requires the addition of 85 kJ of heat per two moles of NaHCO3. (a) Write a balanced thermochemical equation for the reaction.

Textbook Question

Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H1g2 → H21g2 (b) Which has the higher enthalpy under these conditions, 2 H1g2 or H21g2?

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