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Ch.15 - Chemical Equilibrium
All textbooksTro 4th EditionCh.15 - Chemical EquilibriumProblem 39
Chapter 15, Problem 39

Consider the reaction: 2 NO(g) + Br2(g) ⇌ 2 NOBr(g) Kp = 28.4 at 298K In a reaction mixture at equilibrium, the partial pressure of NO is 108 torr and that of Br2 is 126 torr. What is the partial pressure of NOBr in this mixture?

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1
Step 1: Understand the problem. We are given the equilibrium constant (Kp) for the reaction 2NO(g) + Br2(g) ⇌ 2NOBr(g) and the partial pressures of NO and Br2. We need to find the partial pressure of NOBr.
Step 2: Write down the expression for the equilibrium constant (Kp) for the given reaction. Kp = [NOBr]^2 / ([NO]^2 * [Br2])
Step 3: Convert the given pressures from torr to atmospheres because the equilibrium constant is usually given in terms of atmospheres. 1 atm = 760 torr. So, [NO] = 108 torr / 760 torr/atm and [Br2] = 126 torr / 760 torr/atm.
Step 4: Substitute the known values into the equilibrium expression and solve for [NOBr]. Remember that [NOBr] = sqrt(Kp * [NO]^2 * [Br2]).
Step 5: The result will be the partial pressure of NOBr in atmospheres. If needed, convert it back to torr by multiplying by 760 torr/atm.

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Key Concepts

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

Equilibrium Constant (Kp)

The equilibrium constant (Kp) is a numerical value that expresses the ratio of the partial pressures of the products to the reactants at equilibrium for a given reaction at a specific temperature. For the reaction 2NO(g) + Br2(g) ⇌ 2NOBr(g), Kp is calculated using the formula Kp = (P_NOBr^2) / (P_NO^2 * P_Br2), where P represents the partial pressures of the gases involved.
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Partial Pressure

Partial pressure is the pressure exerted by a single component of a gas mixture. It can be determined using Dalton's Law, which states that the total pressure of a gas mixture is equal to the sum of the partial pressures of its individual components. In this context, the partial pressures of NO and Br2 are given, and the partial pressure of NOBr needs to be calculated using the equilibrium constant.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. In this reaction, if the concentrations of NO or Br2 were to change, the system would shift to either the left or right to re-establish equilibrium, which is relevant when considering how the partial pressures relate to Kp.
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Related Practice
Textbook Question

Consider the reaction: N2(g) + 3 H2(g) ⇌ 2 NH3(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (K) [N2] [H2] [NH3] Kc

500 0.115 0.105 0.439 _

575 0.110 _ 0.128 9.6

775 0.120 0.140 _ 0.0584

Textbook Question

Consider the following reaction: H2(g) + I2(g) ⇌ 2 HI(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (°C) [H2] [I2] [HI] Kc

25 0.0355 0.0388 0.922 _

340 _ 0.0455 0.387 9.6

445 0.0485 0.0468 _ 50.2

Textbook Question

Consider the reaction: SO2Cl2(g) ⇌ SO2(g) + Cl2(g) Kp = 2.91⨉103 at 298 K In a reaction at equilibrium, the partial pressure of SO2 is 137 torr and that of Cl2 is 285 torr. What is the partial pressure of SO2Cl2in this mixture?