26870 Chemistry Practice Problems

Explain what happens if a system at equilibrium is subject to one of the following changes and why:

The temperature is raised.

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Explain what happens if a system at equilibrium is subject to one of the following changes and why:

The volume is decreased.

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Explain what happens if a system at equilibrium is subject to one of the following changes and why:

A solid product is added.

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Explain what happens if a system at equilibrium is subject to one of the following changes and why:

The concentration of a reactant is increased.

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For the reaction A → B, the ratio of products to reactants at equilibrium is always the same number, no matter how much A or B is initially present. Interestingly, in contrast, the ratio of products to reactants for the reaction C → 2D does depend on how much of C and D you have initially.

Explain this observation. Which ratio is independent of the starting amounts of C and D?

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Solve each of the expressions for x using the quadratic formula and the x is small approximation. In which of the following expressions is the x is small approximation valid?

x2/(0.01 - x) = 1.3 x 10–4

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Solve each of the expressions for x using the quadratic formula and the x is small approximation. In which of the following expressions is the x is small approximation valid?

x2/(0.2 - x) = 1.3 x 10–4

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Solve each of the expressions for x using the quadratic formula and the x is small approximation. In which of the following expressions is the x is small approximation valid?

x2/(0.2 - x) = 1.3

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Solve each of the expressions for x using the quadratic formula and the x is small approximation. In which of the following expressions is the x is small approximation valid?

x2/(0.2 - x) = 1.3 x 104

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The reactions shown here can be combined to make the overall reaction C(s) + H2O(g) ⇌ CO(g) + H2(g) by reversing some and/or dividing all the coefficients by a number.
a. C(s) + O2( g) ⇌ CO2(g); K = 1.363 x 1069
b. 2H2(g) + O2(g) ⇌ 2H2O(g); K = 1.389 x 1080
c. 2CO(g) + O2(g) ⇌ 2CO2(g); K = 1.363 1069

Determine the value of K.

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The reactions shown here can be combined to make the overall reaction C(s) + H2O(g) ⇌ CO(g) + H2(g) by reversing some and/or dividing all the coefficients by a number.
a. C(s) + O2( g) ⇌ CO2(g); K = 1.363 x 1069
b. 2H2(g) + O2(g) ⇌ 2H2O(g); K = 1.389 x 1080
c. 2CO(g) + O2(g) ⇌ 2CO2(g); K = 1.363 1069

Select the correct formula you would use to determine K.

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Consider the reaction: N2(g) + 3H2(g) → 2NH3(g)

If some hydrogen is added, before the reaction shifts, will the reaction have to shift forward or backward to retain equilibrium? Explain.

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Consider the reaction: N2(g) + 3H2(g) → 2NH3(g)

If some hydrogen is added, before the reaction shifts, will Q be larger or smaller than K? Why?

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Consider the reaction: N2(g) + 3H2(g) → 2NH3(g)

Write the equilibrium constant expression for this reaction.

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Consider the reaction: A(g) ⇌ 2B(g). The graph plots the concentrations of A and B as a function of time at a constant temperature.
The figure shows the concentration as a function of time. Concentration is measured from 0 to 1 mole per liter on the y-axis and time is measured on the x-axis. There are two curves on the plot. Curve A starts at 1 mole per liter, then decreases to approximately 0.6 moles per liter, and then becomes a straight horizontal line. Curve B starts at 0 moles per liter, increases with the same speed as curve A to 0.8 moles per liter, and then becomes a straight horizontal line. These curves cross at the concentration about 0.65 moles per liter.

What is the equilibrium constant for this reaction at this temperature?
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Consider the reaction A(g) ⇌ B(g). The images shown here illustrate equilibrium mixtures of A (red) and g (black) at three different temperatures.
The figure shows illustration equilibrium mixtures at different temperatures. At temperature T1, there are 4 black and 6 red balls in the mixture, at temperature T2 - 5 black and 5 red balls, and at temperature T3 - 8 black and 2 red balls.

At which temperature is the equilibrium constant the largest?
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You may want to reference(Pages 693 - 702) section 15.8 while completing this problem.

Consider the following reaction: I2(g) + Cl2(g) ⇌ 2ICl(g), Kp = 81.9 (at 25 oC)

A reaction mixture at 25oC initially contains PI2 = 0.160 atm, PCl2 = 0.160 atm, and PICl = 0.00 atm. Find the equilibrium partial pressure of ICl at this temperature.

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You may want to reference(Pages 693 - 702) section 15.8 while completing this problem.

Consider the following reaction: I2(g) + Cl2(g) ⇌ 2ICl(g), Kp = 81.9 (at 25 oC)

A reaction mixture at 25oC initially contains PI2 = 0.160 atm, PCl2 = 0.160 atm, and PICl = 0.00 atm. Find the equilibrium partial pressure of Cl2 at this temperature.

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You may want to reference(Pages 693 - 702) section 15.8 while completing this problem.

Consider the following reaction: I2(g) + Cl2(g) ⇌ 2ICl(g), Kp = 81.9 (at 25 oC)

A reaction mixture at 25oC initially contains PI2 = 0.160 atm, PCl2 = 0.160 atm, and PICl = 0.00 atm. Find the equilibrium partial pressure of I2 at this temperature.

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You may want to reference(Pages 693 - 702)Section 15.8 while completing this problem.

Diatomic iodine (I2) decomposes at high temperature to form I atoms according to the reaction: I2(g) ⇌ 2I(g), Kc = 0.011 at 1200 oC

In an equilibrium mixture, the concentration of I2 is 0.18 M. What is the equilibrium concentration of I?

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You may want to reference(Pages 685 - 693) Section 15.7 while completing this problem.

Consider the reaction and its equilibrium constant: N2O4(g) ⇌ 2NO2(g); Kc = 5.85 x 10–3 (at some temperature)

A reaction mixture contains [NO2] = 0.0251 M and [N2O4] = 0.0331 M. Determine the direction in which the reaction will proceed.

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You may want to reference(Pages 685 - 693) Section 15.7 while completing this problem.

Consider the reaction and its equilibrium constant: N2O4(g) ⇌ 2NO2(g); Kc = 5.85 x 10–3 (at some temperature)

A reaction mixture contains [NO2] = 0.0251 M and [N2O4] = 0.0331 M. Calculate Qc at the given concentrations.

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You may want to reference (Pages 693 - 702) Section 15.8 while completing this problem.

Consider the reaction for the decomposition of hydrogen disulfide: 2H2S(g) ⇌ 2H2(g) + S2(g), Kc = 1.67 x 10–7 at 800 oC. A 0.500 L reaction vessel initially contains 0.125 mol of H2S and 0.125 mol of H2 at 800 oC. Find the equilibrium concentration of [S2].

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You may want to reference (Pages 693 - 702) Section 15.8 while completing this problem.

The reaction N2(g) + O2(g) ⇌ 2NO(g) is carried out at a temperature at which Kc = 0.060. The reaction mixture starts with only the product, [NO] = 0.0400 M, and no reactants. Find the equilibrium concentrations of NO at equilibrium.


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You may want to reference (Pages 693 - 702) Section 15.8 while completing this problem.

The reaction N2(g) + O2(g) ⇌ 2NO(g) is carried out at a temperature at which Kc = 0.060. The reaction mixture starts with only the product, [NO] = 0.0400 M, and no reactants. Find the equilibrium concentrations of O2 at equilibrium.


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