Nitrosyl bromide decomposes at elevated temperature according to The reaction mixture…

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Nitrosyl bromide decomposes at elevated temperature according to

2\,\text{NOBr}(g) \rightleftharpoons 2\,\text{NO}(g) + \text{Br}_2(g)

The reaction mixture described below is sealed in a 4.00 L flask at 523 K: •

n_{\text{NOBr}} = 0.400\,\text{mol}

•

n_{\text{NO}} = 0.200\,\text{mol}

•

n_{\text{Br}_2} = 0.100\,\text{mol}

At 523 K the equilibrium constant is

K_c = 2.0 \times 10^{-2}

. (a) Derive an expression for the equilibrium constant in terms of the single unknown change variable

x

that represents the number of moles of

\text{NOBr}

that decompose. (b) Using the relationship obtained in part (a), determine the numerical value of

x

and hence calculate the equilibrium concentrations (in mol L

^{-1}

) of all species present. (c) Compute the total pressure in the flask at equilibrium, assuming ideal–gas behavior at 523 K. (d) Calculate the fraction of the initial

\text{NOBr}

that has decomposed at equilibrium and interpret what this reveals about the position of equilibrium for this system.

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