Chm Mod 6

Δngas = -1

3O2 (g) ⇌ 2O3 (g)

Large K

Equilibrium favors the products; there will be more products than reactants at equilibrium

Small K

Equilibrium favors the reactants; there will be more reactants than products at equilibrium.

Δngas = 0

H2 (g) + I2 (g) ⇌ 2HI (g)

Which of the following is the correct expression for the relationship between Kc and KP?

KP = Kc(RT)Δn(gas)

A sample of solid C is placed in a sealed reaction vessel containing 2.0 atm H2 (g) and allowed to react according to the equation C (s) + 2H2 (g) ⇌ CH4 (g). At equilibrium the partial pressure of CH4 = 0.39 atm. Calculate Kp for the reaction.

Kp = 0.39/(2.0-0.78)2 = 0.26

As a reaction proceeds, the value of Q _____.

increases or decreases, as necessary, until it reaches the value of K

The law of mass action reflects the observation that an equilibrium state is reached by a chemical system regardless of the ___ concentrations of reacting substances. In other words, a chemical system can reach equilibrium either from the reactants or from the ___.

initial, products

A 1-L flask contains 0.50 mol SO2Cl2, 0.30 mol SO2, and 0.16 mol Cl2, which react according to the equation SO2Cl2 (g) ⇌ SO2 (g) + Cl2 (g), Kc = 0.011 for the reaction temperature. Select all the options that correctly interpret the data provided.

[SO2Cl2]eqm will be greater than 0.50 M. Kc = 0.011 =(0.30-x)(0.16-x)(0.50+x) The reaction will proceed toward the reactant.

If the value of K for the forward reaction is less than 1, the value of K for the reverse reaction is _____ than 1.

greater

Which of the following options correctly describe the equilibrium constant K? Select all that apply.

- K = k(fwd)/k(rev) for a system at equilibrium. - The value of K is characteristic of a particular equilibrium system. - K expresses a particular ratio of equilibrium concentrations of products and reactants.

Which of the following options correctly reflect the equation relating KP and Kc for a given reaction? Select all that apply.

- T is the temperature in kelvin. - Δngas is determined from the coefficients of the balanced equation. - R = 0.0821 atm⋅L/mol⋅K

Which of the following statements correctly describe the rate equations and rate constants for a system at equilibrium? Select all that apply.

- The ratio [products]/[reactants] remains constant although the forward and reverse reactions continue to occur. - The rate of the forward reaction is equal to the rate of the reverse reaction.

Which of the following statements correctly describe a chemical system at equilibrium? Select all that apply.

- There is no longer a change in concentration of reactants and products over time. - The forward and reverse reactions occur at equal rates.

Given the following data: H2C2O4 (aq) ⇌ 2H+ (aq) + C2O2−4 (aq) ; K1c = 3.8 × 10-6 HF (aq) ⇌ H+ (aq) + F- (aq) ; K2c = 6.8 × 10-4 Find Kc for the reaction: 2HF (aq) + C2O2−4 (aq) ⇌ H2C2O4 (aq) + 2F- (aq)

0.12

Given the following data: 2NO2 (g) ⇌ 2NO (g) + O2 (g); K = 1.1 × 10-5 2NO (g) ⇌ N2 (g) + O2 (g); K = 4.4 × 1018 What is the value of K for the overall reaction: 2NO2 (g) ⇌ N2 (g) + 2O2 (g)?

4.8 × 10e13

Which of the following statements correctly describes a system at equilibrium for which K = 1.2?

Both products and reactants are present in significant amounts at equilibrium.

Intermediate K

Both reactants and products will be present in significant amounts at equilibrium

Δngas = 1

CO2 (s) ⇌ CO2 (g)

Select all the options that correctly reflect the steps required to determine the direction in which the following reaction will proceed at the given concentrations 2NO2Cl (g) ⇌ 2NO2 (g) + Cl2 (g), where Kc = 3.21 × 10-4 if [NO2Cl] = 0.012 M, [NO2] = 0.018 M, and [Cl2] = 0.026 M.

Qc = (0.026)(0.018)2/(0.012)2 = 5.9 × 10-2 Since Qc > Kc, the reaction will proceed toward the reactants.

Q > K

Shift to reactants

What is the benchmark for deciding if we may assume [A]init - x = [A]init when solving equilibrium problems?

The assumption is okay if [A]init/Kc > 400.

0.20 mol of NO (g) is placed in a 1-L container with 0.15 mol of Br2 (g). These will react according to the balanced equation: 2NOBr (g) ⇌ 2NO (g) + Br2 (g). Given that [NOBr] = 0.18 M at equilibrium, select all the options that correctly describe the steps required to calculate Kc for the reaction.

The initial [NOBr] = 0 M. x = 0.182 = 0.09 If the change in [Br2] = -x, then the change in [NOBr] = +2x.

0.45 mol PCl5 (g) is placed in a sealed 2.0-L container and reacts according to the equation: PCl5 (g) ⇌ PCl3 (g) + Cl2 (g). If [Cl2] = 0.10 M at equilibrium, select all the options that correctly reflect the steps required to calculate Kc.

The initial [PCl5] = 0.23 M. At equilibrium [PCl3] = 0.10 M. Kc = (0.10)(0.10)/(0.13)

If the equilibrium constant K for a particular reaction is 1.22 x 10e14, which of the following statements correctly describes the reaction?

There are large concentrations of products compared to reactants.

The equilibrium constant K for a system at equilibrium ____ expresses a particular ratio of equilibrium of products and reactants at a particular ___. The value of K is also equal to the ratio of the rate ___ for the forward and reverse reactions.

concentration, temperature, constants

In a closed system a reversible chemical reaction will reach a state of dynamic chemical ___ when the rate of the forward reaction is ___ to/than the rate of the reverse reaction.

equilibrium, equal

The equilibrium constant expression for a particular reaction is given by Kc = (2x)2(0.1-x)(0.2-2x). This equation cannot be simplified by taking square roots on both sides as the denominator is not a(n) square. In this case, the formula can be used to solve for x.

perfect quadratic

When a system reaches equilibrium, the ______ of the forward and reverse reactions are equal and the ratio of the forward over the reverse ______ equals the equilibrium constant, K.

rates; rate constants

The value of the equilibrium constant K is a measure of how far the reaction proceeds toward the products at a given temperature. A small value of K indicates that the reaction favors the _____, whereas a large value of K indicates that the _____ will be present in a higher proportion.

reactants; products Reason: Correct. K = 1, it indicates that reactants and products are present in equal proportions.

Q = K

reaction is at equilibrium

Q < K

shift to products

N2O4 (g) ⇌ 2NO2 (g); Kc = 6.1 × 10-3 at 298 K If [N2O4] at the start of the reaction = 2.0 M, select ALL the options that correctly show how to calculate [NO2] at equilibrium. Assume that the change in [NO2] = +2x.

x = 2.8% of [N2O4]init so the simplifying assumption is justified. If the change in [NO2] = +2x then [N2O4]eqm = (2.0 - x). Kc = 6.1 × 10-3 ≈ 4x22.0

For the reaction CO (g) + Cl2 (g) ⇌ COCl2 (g), Kp at 1000 K = 3.9 × 10-2. Which of the following options correctly reflect the steps required to calculate Kc at 1000 K? Select all that apply.

Δngas = -1 Kc = (3.9 × 10-2)(0.0821 × 1000)1 = 3.2