Textbook Question
Write an expression for the equilibrium constant of each chemical equation.
a. SbCl5(g) ⇌ SbCl3(g) + Cl2(g)
b.2 BrNO(g) ⇌ 2 NO(g) + Br2(g)
c. CH4(g) + 2 H2S(g) ⇌ CS2(g) + 4 H2(g)
d. 2 CO(g) + O2(g) ⇌ 2 CO2(g)
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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 5
Nitrogen dioxide dimerizes according to the reaction: 2 NO2(g) ⇌ N2O4(g) Kp = 6.7 at 298 K. A 2.25-L container contains 0.055 mol of NO2 and 0.082 mol of N2O4 at 298 K. Is the reaction at equilibrium? If not, in which direction will the reaction proceed?
Verified step by step guidance1
Calculate the initial partial pressures of NO2 and N2O4 using the ideal gas law: P = (nRT)/V, where n is the number of moles, R is the ideal gas constant (0.0821 L·atm/mol·K), T is the temperature in Kelvin, and V is the volume of the container.
Determine the reaction quotient, Qp, using the expression Qp = (P_{N2O4}) / (P_{NO2})^2, where P_{N2O4} and P_{NO2} are the partial pressures of N2O4 and NO2, respectively.
Compare the calculated Qp to the given equilibrium constant Kp. If Qp < Kp, the reaction will proceed in the forward direction to reach equilibrium. If Qp > Kp, the reaction will proceed in the reverse direction. If Qp = Kp, the reaction is at equilibrium.
Analyze the direction of the reaction based on the comparison of Qp and Kp to determine if the reaction will shift towards the formation of more products (N2O4) or reactants (NO2).
Conclude whether the reaction is at equilibrium or predict the direction in which the reaction will proceed to reach equilibrium.
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 concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. For the reaction 2 NO2(g) ⇌ N2O4(g), Kp = 6.7 indicates the extent to which the reaction favors the formation of products (N2O4) over reactants (NO2) at 298 K.
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Equilibrium Constant Expressions
Reaction Quotient (Q)
The reaction quotient (Q) is calculated using the current concentrations of the reactants and products in a system, similar to Kp but not necessarily at equilibrium. By comparing Q to Kp, one can determine the direction in which the reaction will shift to reach equilibrium. If Q < Kp, the reaction will proceed to the right (toward products); if Q > Kp, it will shift to the left (toward reactants).
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Calculating Concentrations
To determine if the reaction is at equilibrium, one must calculate the concentrations of NO2 and N2O4 in the 2.25-L container. Concentration is found by dividing the number of moles by the volume of the container. This allows for the calculation of Q, which can then be compared to Kp to assess the state of the reaction.
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