# Question 13.8: Writing Equilibrium Equations for Heterogeneous Equilibria W......

Writing Equilibrium Equations for Heterogeneous Equilibria

Write the equilibrium equation for each of the following reactions:

(a) $CO_2$(g) + C(s) $\rightleftharpoons$ 2 CO(g)

(b) $\mathrm{Hg}(l)+\mathrm{Hg}^{2+}(a q) \rightleftharpoons \mathrm{Hg}_2^{2+}(a q)$

STRATEGY

Write the usual equilibrium-constant expressions but omit the pure solid carbon in part (a) and the pure liquid mercury in part (b) because the ratio of their concentrations to their concentrations in the standard state is equal to 1.

Step-by-Step
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(a) $K_{\mathrm{c}}=\frac{[\mathrm{CO}]^2}{\left[\mathrm{CO}_2\right]}$

Alternatively, because CO and $CO_2$ are gases, the equilibrium equation can be written using partial pressures:

$K_{\mathrm{p}}=\frac{\left(P_{\mathrm{CO}}\right)^2}{P_{\mathrm{CO}_2}}$

The relationship between $K_p$ and $K_c$ is $K_p = K_c(RT)^{Δn} = K_c$(RT), because Δn = 2 – 1 = 1.

(b) $K_c=\frac{\left[\mathrm{Hg}_2^{2+}\right]}{\left[\mathrm{Hg}^{2+}\right]}$

In this case, it’s not appropriate to write an expression for $K_p$ because none of the reactants or products is a gas.

Question: 13.6

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K_{\mathrm{p}}=\frac{\left(P_{\mathrm{CS}_2...
Question: 13.16

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Question: 13.13

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Question: 13.12

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Question: 13.11

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Question: 13.10

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Question: 13.9

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