SB 16.4 - 16.5

K for the dissociation of iron(III) hydroxide in water (shown below) is equal to 1.1 x 10-36 at 25oC. Determine ΔGo (in kJ/mol) at 25oC for the reaction. Fe(OH)3(s) ⇌ Fe3+(aq) + 3OH-(aq).

+205 kJ/mol

The reaction to form BrF3 (shown below) has a ΔG° of -459 kJ/mol. If the initial partial pressures are PF2 = 1.75 atm and PBrF3 = 0.187 atm and the reaction temperature is 300 K, what is ΔG for the reaction? Br2(l) + 3F2(g) → 2BrF3(g)

-472 kJ/mol

The magnitude of K correlates with the sign of ΔGo. Select all the correct statements that apply about this relationship.

-A reaction with a positive ΔGo will result in an equilibrium mixture composed primarily of reactants. -A reaction with a very large K value has a negative ΔGo.

You are given Kc as well as the initial reactant concentrations for a chemical system at a particular temperature. Select any steps for determining the equilibrium concentrations of the reactants and products that are not correct.

-For each species in the equilibrium, multiply the stoichiometric coefficient by x to obtain the equilibrium concentration in terms of x. -Use the initial concentrations given to calculate the value of Kc.

A sealed 1-L flask contains 0.50 mol SO2Cl2, 0.30 mol SO2, and 0.16 mol Cl2, which react according to the chemical equation SO2Cl2 (g) ⇌ SO2 (g) + Cl2 (g). Kc = 0.011 for the reaction temperature.

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

For the reaction 2NO2Cl (g) ⇌ 2NO2 (g) + Cl2 (g), Kc = 3.21 × 10-4. If [NO2Cl] = 0.012 M, [NO2] = 0.018 M, and [Cl2] = 0.026 M, which of the following correctly reflect the steps required to determine the direction in which the reaction will proceed? Select all that apply.

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

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)

Explain the importance of the equation ΔGo = -RT ln K.

-ΔGo can be calculated from tabulated thermodynamic data. -The magnitude and sign of ΔGo correlate to how large or small is the value of K.

You are given Kc as well as the initial reactant concentrations for a chemical system at a particular temperature. Rank the steps for determining the equilibrium concentrations of the reactants and products in the order that you should carry them out.

1. Construct an equilibrium table and fill in the initial concentrations given 2. Define x as the amount of a particular species consumed 3. Use the stoichiometry of the balanced chemical equation to define, in terms of x, the amounts of other species consumed or produced in the reaction 4. For each species, add the change in concentrations (in terms of x) to the initial concentrations to obtain the equilibrium concentration 5. Use the equilibrium expression, the equilibrium concentrations (in terms of x), and the given value of Kc to solve for the value of x 6. Using the value of x that you calculated determine the equilibrium concentrations of all species

When a reaction is at equilibrium, the reaction quotient Q is always equal to ____ and ΔG is equal to ____.

K; zero

0.50 mol of SO3 (g) is placed in a sealed 1-L container at 700°C and reacts according to the equation: 2SO3 (g) ⇌ 2SO2 (g) + O2 (g). If [O2] at equilibrium = 0.15 M, which of the following gives the correct calculation for Kc?

Kc = (0.15)(0.30)^2/(0.20)^2 = 0.34

1.9 moles of HI are added to an evacuated, sealed 10.-L container and allowed to decompose according to the chemical equation: H2 (g) +I2 (g) ⇌ 2HI (g); Kc = 1.26 × 10−3

Kc = 1.26 ×10-3 = (0.19 -2x)2x2 The initial HI = 0.19 M. If the change in H2 = +x, then at equilibrium I2 = x.

1.9 moles of HI are added to an evacuated, sealed 10.-L container and allowed to decompose according to the chemical equation: H2 (g) +I2 (g) ⇌ 2HI (g); Kc = 1.26 × 10−3H2 (g) + I2 (g) ⇌ 2HI (g); Kc = 1.26 × 10^-3

Kc = 1.26 ×10^-3 = (0.19 -2x)^2/x^2 If the change in H2 = +x, then at equilibrium I2 = x. The initial HI = 0.19 M.

Q < 1

The forward reaction will be more favored and the reverse reaction less favored than at standard conditions.

As the reaction quotient Q increases, what is the effect on the spontaneity of a given reaction?

The reaction becomes less spontaneous.

Q < K

The reaction proceeds toward the products.

Q > K

The reaction proceeds toward the reactants.

The reaction 2HCl(g) ⇌ H2(g) + Cl2(g) has a ΔG° of 191 kJ/mol. A reaction mixture contains PHCl = 0.40 atm, PH2 = 0.20 atm and PCl2 = 0.20 atm at 300 K. Predict the direction in which the reaction will proceed to spontaneously establish equilibrium.

The reaction will proceed to the left spontaneously to achieve equilibrium.

At 100oC, KP = 60.6 for the chemical system 2NOBr (g) ⇌ 2NO (g) + Br2 (g). In an experiment, 0.10 atm of each gas is placed in a sealed container. In which direction will the reaction proceed?

The reaction will proceed toward the products.

At 100oC, KP = 60.6 for the chemical system 2NOBr (g) ⇌ 2NO (g) + Br2 (g). In an experiment, 0.10 atm of each gas is placed in a sealed container. In which direction will the reaction proceed? Multiple choice question.

The reaction will proceed toward the products.

Q > 1

The reverse reaction will be more favored and the forward reaction less favored than at standard conditions.

Q = K

The system is at equilibrium and no net reaction occurs.

Q = 1

There will be no change in spontaneity from standard conditions.

A sealed 1-L flask contains 0.50 mol SO3, 0.20 mol SO2, and 0.30 mol O2, which react according to the chemical equation 2SO3 (g) ⇌ 2SO2 (g) + O2 (g); Kc = 59. At equilibrium, [O2] = 0.52 M.

[SO2]eq = 0.64 M The reaction will proceed toward the products. Kc = 59 = (0.20+2x)^2(0.30+x)/(0.50−2x)^2

As a reaction proceeds in the reverse direction to establish equilibrium, the value of Q _____.

decreases

As a reaction proceeds in the forward direction to establish equilibrium, the value of Q _____.

increases

When Q < K, the reaction will proceed such that the amounts of the _____ decrease and the amounts of the _____ increase.

reactants, products

The value of Q equals _____ when an initial experimental mixture contains only reactants. In order to move towards equilibrium reactant concentrations decrease and product concentrations increase.

zero Reason: Q = [Products]n/[Reactants]m= 0 when [Products] = 0.

K >> 1

ΔGo < 0 and the reaction is spontaneous as written

Under equilibrium conditions, the equation ΔG = ΔGo + RT ln Q simplifies to which of the following?

ΔGo = -RT ln K

K << 1

ΔGo > 0 and the reaction is nonspontaneous as written