When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates Ag⁺(aq) + Cl^-(aq) → AgCl(s) H = -65.5 kJ (a) Calculate H for the production of 0.450 mol of AgCl by this reaction. (b) Calculate H for the production of 9.00 g of AgCl. (c) Calculate H when 9.25⨉10^-4 mol of AgCl dissolves in water.

검증된 단계별 안내

Identify the given enthalpy change (H) for the formation of 1 mole of AgCl, which is -65.5 kJ/mol.

For part (a), use the stoichiometry of the reaction to calculate the total enthalpy change for the formation of 0.450 mol of AgCl. Multiply the moles of AgCl by the enthalpy change per mole.

For part (b), first convert the mass of AgCl (9.00 g) to moles using the molar mass of AgCl (Ag: 107.87 g/mol, Cl: 35.45 g/mol). Then, calculate the enthalpy change by multiplying the moles of AgCl by the enthalpy change per mole.

For part (c), since the reaction of AgCl dissolving is the reverse of the precipitation, the sign of the enthalpy change will be opposite. Calculate the enthalpy change for the dissolution of 9.25⨉10^-4 mol of AgCl by multiplying the moles by the negative of the enthalpy change per mole.

Ensure all calculations consider the correct sign of the enthalpy change, as it indicates whether the reaction is exothermic (-) or endothermic (+).

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주요 개념

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Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the amount of substance produced or consumed in a reaction, using mole ratios derived from the coefficients in the balanced equation. In this case, understanding the stoichiometry of the reaction between silver ions and chloride ions is essential for calculating the enthalpy change (ΔH) for different amounts of silver chloride (AgCl).

Enthalpy Change (ΔH)

Enthalpy change (ΔH) is a measure of the heat absorbed or released during a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). In the given reaction, the negative ΔH value of -65.5 kJ signifies that the formation of AgCl from its ions is exothermic, which is crucial for calculating the heat change for different quantities of AgCl produced or dissolved.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For example, to calculate the enthalpy change for the production of 9.00 g of AgCl, one must first determine the molar mass of AgCl to convert grams to moles, enabling the application of the stoichiometric relationships and ΔH.