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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 16g

Write the expressions for 𝐾𝑐 for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous. (g) 2 C8H18(𝑙) + 25 O2(𝑔) β‡Œ 16 CO2(𝑔) + 18 H2O(𝑙)

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Key Concepts

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

Equilibrium Constant (Kc)

The equilibrium constant, Kc, is a numerical value that expresses the ratio of the concentrations of products to the concentrations of reactants at equilibrium for a given reaction at a specific temperature. It is calculated using the formula Kc = [products]^[coefficients] / [reactants]^[coefficients]. Understanding Kc is essential for predicting the direction of a reaction and the extent to which reactants are converted into products.
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Homogeneous vs. Heterogeneous Reactions

Homogeneous reactions occur when all reactants and products are in the same phase (solid, liquid, or gas), while heterogeneous reactions involve reactants and products in different phases. This distinction is important because it affects how concentrations are expressed in the Kc expression. For example, in a heterogeneous reaction, solids and liquids are not included in the Kc expression, as their concentrations do not change significantly.
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Phase Representation in Kc Expressions

In Kc expressions, only the concentrations of gaseous and aqueous species are included, while pure solids and liquids are omitted. This is because the activity of pure solids and liquids is considered to be constant. Understanding how to represent different phases in Kc expressions is crucial for accurately writing the equilibrium constant for a given reaction, as seen in the provided reaction involving liquid and gaseous components.
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