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Ch.9 - Thermochemistry: Chemical Energy
Chapter 9, Problem 155

Reaction of gaseous fluorine with compound X yields a sin- gle product Y, whose mass percent composition is 61.7% F and 38.3% Cl. (c) Calculate ΔH° for the synthesis of Y using the following information: 2 CIF1g2 + O21g2 S Cl2O1g2 + OF21g2 ΔH° = + 205.4 kJ 2 CIF31l2 + 2 O21g2 S Cl2O1g2 + 3 OF21g2 ΔH° = + 532.8 kJ OF21g2 ΔH°f = + 24.5 kJ>mol

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Key Concepts

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

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the conservation of mass. It involves using balanced chemical equations to determine the relationships between the amounts of substances consumed and produced. Understanding stoichiometry is essential for calculating the quantities needed for reactions and for interpreting the results of chemical equations.
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Enthalpy Change (ΔH°)

Enthalpy change (ΔH°) refers to the heat content change during a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). Knowing the enthalpy changes of related reactions allows for the application of Hess's law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps.
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Mass Percent Composition

Mass percent composition is a way to express the concentration of an element in a compound as a percentage of the total mass of the compound. It is calculated by dividing the mass of the element by the total mass of the compound and multiplying by 100. This concept is crucial for determining the empirical formula of a compound and for understanding the proportions of elements involved in chemical reactions.
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