Using values from Appendix C, calculate the standard enthalpy change for each of the following reactions: (a) 2 SO2(g) + O2(g) → 2 SO3(g) (b) Mg(OH)2(s) → MgO(s) + H2O(l) (c) N2O4(g) + 4 H2(g) → N2(g) + 4 H2O(g) (d) SiCl4(l) + 2 H2O(l) → SiO2(s) + 4 HCl(g)

Verified step by step guidance

Step 1: Identify the standard enthalpy of formation (ΔH_f^°) for each reactant and product in the given reactions from Appendix C.

Step 2: For each reaction, apply Hess's Law to calculate the standard enthalpy change (ΔH_rxn^°) using the formula: ΔH_rxn^° = Σ(ΔH_f^° of products) - Σ(ΔH_f^° of reactants).

Step 3: For reaction (a) 2 SO2(g) + O2(g) → 2 SO3(g), calculate ΔH_rxn^° by substituting the ΔH_f^° values of SO3(g), SO2(g), and O2(g) into the formula.

Step 4: For reaction (b) Mg(OH)2(s) → MgO(s) + H2O(l), calculate ΔH_rxn^° by substituting the ΔH_f^° values of MgO(s), H2O(l), and Mg(OH)2(s) into the formula.

Step 5: Repeat the process for reactions (c) and (d), substituting the appropriate ΔH_f^° values for each reactant and product to find the ΔH_rxn^° for each reaction.

Key Concepts

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

Standard Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This value is crucial for calculating the enthalpy change of a reaction using Hess's law, as it allows for the determination of the energy required or released during the formation of products and reactants.

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows chemists to calculate the enthalpy change for complex reactions by breaking them down into simpler steps for which enthalpy values are known.

Stoichiometry in Reactions

Stoichiometry involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. Understanding stoichiometry is essential for calculating the standard enthalpy change, as it ensures that the correct coefficients are used when applying the enthalpy values from Appendix C to the balanced chemical equations provided.

Recommended video:

Guided course

01:16

Stoichiometry Concept

Related Practice

Textbook Question

Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C: (a) CH₃OH(l)

Textbook Question

Acetylene (C₂H₂(g)) is used for welding because oxyacetylene is the hottest burning common fuel gas. Using standard enthalpies of formation, calculate the quantity of heat produced when 10 g of acetylene is completely combusted in air under standard conditions.

Textbook Question

Using values from Appendix C, calculate the value of H for each of the following reactions: (a) CaO(s) + 2 HF(g) → CaF₂(s) + H₂O(g) (b) Fe₂O₃(s) + 3 C(s) → 2 Fe(s) + 3CO(g) (c) 2 CO(g) + 2 NO(g) → N₂(s) + 2 CO₂(g) (d) 4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 6 H₂Og)

Textbook Question

Complete combustion of 1 mol of acetone (C₃H₆O) liberates 1790 kJ: C₃H₆O(l) + 4 O₂(g) → 3 CO₂(g) + 3 H₂O(l) ΔH° = -1790 kJ Using this information together with the standard enthalpies of formation of O₂(g), CO₂(g), and H₂O(l) from Appendix C, calculate the standard enthalpy of formation of acetone.

Textbook Question

Calcium carbide (CaC₂) reacts with water to form acetylene (C₂H₂) and Ca(OH)₂. From the following enthalpy of reaction data and data in Appendix C, calculate H°_f for CaC₂(s): CaC₂(s) + 2 H₂O(l) → Ca(OH₂)(s) + C₂H₂(g) ΔH° = -127.2 kJ