Ch.15 - Chemical Equilibrium

Problem 83b

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Chapter 15, Problem 83b

Nitric oxide (NO) reacts readily with chlorine gas as follows: 2 NO(𝑔) + Cl₂(𝑔) ⇌ 2 NOCl(𝑔) At 700 K, the equilibrium constant Kp for this reaction is 0.26. Predict the behavior of each of the following mixtures at this temperature and indicate whether or not the mixtures are at equilibrium. If not, state whether the mixture will need to produce more products or reactants to reach equilibrium. (b) P_NO = 0.12 atm, P_Cl2 = 0.10 atm, P_NOCl = 0.050 atm

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Calculate the reaction quotient, Qp, using the formula: Qp = (P_{NOCl}^2) / (P_{NO}^2 * P_{Cl2}).

Substitute the given partial pressures into the Qp expression: P_{NO} = 0.12 atm, P_{Cl2} = 0.10 atm, P_{NOCl} = 0.050 atm.

Compare the calculated Qp value with the given equilibrium constant Kp = 0.26.

If Qp < Kp, the reaction will proceed in the forward direction to produce more products (NOCl) to reach equilibrium.

If Qp > Kp, the reaction will proceed in the reverse direction to produce more reactants (NO and Cl2) to reach equilibrium.

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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 2 NO(g) + Cl2(g) ⇌ 2 NOCl(g), Kp = 0.26 indicates that at equilibrium, the concentration of NOCl is relatively low compared to NO and Cl2. This constant helps predict the direction in which a reaction will shift to reach equilibrium.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. In the context of the given reaction, if the concentrations of reactants or products are altered, the system will shift towards the side that reduces the effect of the change, either producing more products or reactants as needed.

Reaction Quotient (Q)

The reaction quotient (Q) is a measure of the relative amounts of products and reactants present in a reaction mixture at any point in time, calculated using the same formula as Kp. By comparing Q to Kp, one can determine the direction in which the reaction will proceed to reach equilibrium. If Q < Kp, the reaction will shift to the right to produce more products; if Q > Kp, it will shift to the left to produce more reactants.

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Related Practice

For the equilibrium PH₃BCl₃(𝑠) ⇌ PH₃(𝑔) + BCl₃(𝑔) 𝐾_𝑝 = 0.052 at 60 °C. (b) After 3.00 g of solid PH₃BCl₃ is added to a closed 1.500-L vessel at 60 °C, the vessel is charged with 0.0500 g of BCl₃(𝑔). What is the equilibrium concentration of PH₃?

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Open Question

Solid NH4SH is introduced into an evacuated flask at 24 _x001F_C. The following reaction takes place: NH4SH(s) ⇌ NH3(g) + H2S(g). At equilibrium, the total pressure (for NH3 and H2S taken together) is 0.614 atm. What is Kp for this equilibrium at 24 _x001F_C?

Textbook Question

A 0.831-g sample of SO₃ is placed in a 1.00-L container and heated to 1100 K. The SO₃ decomposes to SO₂ and O₂: 2SO₃(𝑔) ⇌ 2 SO₂(𝑔) + O₂(𝑔) At equilibrium, the total pressure in the container is 1.300 atm. Find the values of 𝐾_𝑝 and 𝐾_𝑐 for this reaction at 1100 K.

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Textbook Question

At 900 °C, 𝐾_𝑐= 0.0108 for the reaction

CaCO₃(𝑠) ⇌ CaO(𝑠) + CO₂(𝑔)

A mixture of CaCO₃, CaO, and CO₂ is placed in a 10.0-L vessel at 900°C. For the following mixtures, will the amount of CaCO3 increase, decrease, or remain the same as the system approaches equilibrium?

When 1.50 mol CO2 and 1.50 mol H2 are placed in a 3.00-L container at 395 _x001F_C, the following reaction occurs: CO2(g) + H2(g) ⇌ CO(g) + H2O(g). If Kc = 0.802, what are the concentrations of each substance in the equilibrium mixture?

Textbook Question

The equilibrium constant constant 𝐾_𝑐 for C(𝑠) + CO₂(𝑔) ⇌ 2 CO(𝑔) is 1.9 at 1000 K and 0.133 at 298 K. (b) If excess C is allowed to react with 25.0 g of CO₂ in a 3.00-L vessel at 1000 K, how many grams of C are consumed?

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