Ch.5 - Thermochemistry

Problem 40a

Chapter 5, Problem 40a

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.

Verified step by step guidance

Identify the reactants and products in the decomposition reaction: NaHCO3(s) decomposes into Na2CO3(s), H2O(l), and CO2(g).

Write the unbalanced chemical equation for the decomposition: NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g).

Balance the chemical equation by ensuring the number of each type of atom is the same on both sides. For this reaction, you need 2 moles of NaHCO3 to produce 1 mole of Na2CO3, 1 mole of H2O, and 1 mole of CO2. The balanced equation is: 2 NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g).

Incorporate the thermochemical data into the balanced equation. Since 85 kJ of heat is required for the decomposition of 2 moles of NaHCO3, this energy change is written on the reactant side as it is an endothermic reaction: 2 NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g).

Verify that the equation is balanced both in terms of mass and energy, ensuring that the stoichiometry and the thermochemical data are correctly represented.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Thermochemical Equations

A thermochemical equation is a balanced chemical equation that includes the enthalpy change (ΔH) associated with the reaction. It indicates whether the reaction is exothermic (releases heat) or endothermic (absorbs heat). In this case, the decomposition of sodium bicarbonate is endothermic, requiring heat input, which should be included in the equation.

Balancing Chemical Equations

Balancing chemical equations involves ensuring that the number of atoms of each element is the same on both the reactant and product sides. This is crucial for obeying the law of conservation of mass. For the decomposition of sodium bicarbonate, the balanced equation must reflect the stoichiometry of the reactants and products accurately.

Enthalpy Change (ΔH)

Enthalpy change (ΔH) is a measure of the heat absorbed or released during a chemical reaction at constant pressure. In this scenario, the reaction absorbs 85 kJ of heat for every two moles of sodium bicarbonate decomposed, indicating a positive ΔH value. This information is essential for writing the thermochemical equation correctly.

Recommended video:

Guided course

02:34

Enthalpy of Formation

Related Practice

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?

views

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. (a) Write a balanced thermochemical equation for this reaction.

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.

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 H(g) → H₂(g) (a) Using the thermodynamic data in Appendix C, calculate the enthalpy change for this reaction per mole of H₂.

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 H(g) → H₂(g) (b) Which has the higher enthalpy under these conditions, 2 H(g) or H₂(g)?

Textbook Question

Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol I₂(s) or 1 mol I₂(g) at the same temperature

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.

Verified video answer for a similar problem:

Key Concepts

Thermochemical Equations

Balancing Chemical Equations

Enthalpy Change (ΔH)

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.