Smartbook Ch. 20 Pt. 2

In the expression ΔG = RT ln(Q/K), ΔG = ___ when Q is equal to K, i.e., when Q/K = ___

0, 1

Which of the following options correctly describe the Gibbs free energy change (ΔG) of a system?

The free energy change for a process is a measure of the useful work it can provide. ΔG is a measure of the spontaneity of a process.

For the hypothetical reaction A → 2B, the equilibrium constant Kc = 0.01. Rank the answers below in order of increasing ΔGrxn, starting with the reaction that has the most negative value for ΔGrxn at the top of the list.

[A]= 1 M [B]= 0.01 M [A]= 1 M [B]= 0.1 M [A]= 1 M [B]= 1 M

Q < K Q > K Q = K

ΔG < 0 ΔG > 0 ΔG = 0

Which of the following symbols denotes a standard free energy change?

ΔGo

Under standard-state conditions, the equation ΔG = RT ln(Q/K) simplifies to which of the following?

ΔG° = -RT ln(K)

Calculate the free energy change for the reaction Cu2O (s) → Cu (s) + 1212O2 (g) at 375 K if ΔH = 168 kJ/mol and ΔS = -9.63 J/K⋅mol.

+172 kJ/mol (ΔG = 168 kJ/mol - 375 K(-9.63J/mol⋅K×1kJ1000K)-9.63J/mol⋅K×1kJ1000K = 168 + 3.61 = +172 kJ/mol)

Ksp for iron(III) hydroxide [Fe(OH)3] is equal to 1.1 x 10-36 at 25oC. Determine ΔGo (in kJ/mol) at 25oC for the reaction represented by the equation Fe(OH)3 (s) ⇌ Fe3+ (aq) + 3OH- (aq).

+205 kJ/mol (ΔG = -8.314 x 298 x ln(1.1 x 10-36) = 205,000 J/mol = 205 kJ/mol)

A reaction taking place at 100oC has an entropy change of 200 J/K and an enthalpy change of -20 kJ. Which of the following expressions would be used to calculate ΔG under these conditions?

-20,000 - (373)(200) convert kJ to J

Using the data provided in the table, calculate the equilibrium constant KP at 25oC for the reaction 2O3 (g) ⇌ 3O2 (g). O3 (g) = 163.4 delta G standard O2 (g) = 0

2.1 x 10^57 (ΔGorxn = 3(0) - 2(163.4) = -326.8 kJ/mol ln K = -ΔG°RTΔG°RT = -(-326.8×10008.314×298)-326.8×10008.314×298 = 132 K = e132 = 2.1 x 10^57)

The following reaction takes place at 25°C and has a standard cell potential equal to +0.47 V: Cu2+ (aq) + Pb (s) → Pb2+ (aq) + Cu (s) What is the equilibrium constant for this reaction?

7.9 × 10^15 (Since there are 2 electrons transferred in this reaction, n = 2. 0.47 = 0.059220.05922 log K log K = 0.47×20.05920.47×20.0592 = 15.9 K = 10^15.9 = 7.9 × 10^15)

Since entropy is typically tabulated in units of ___/ K and standard enthalpies are typically tabulated in units of ___/ mol, it is usually necessary to perform a unit conversion when using the formula ΔG = ΔH - TΔS to calculate the Gibbs free energy.

J, kJ

ΔGo = 0 ΔGo = +100 kJ ΔGo = -100 kJ ΔGo = -10 kJ

K = 1 K = 3 x 10-18 K = 3 x 1017 K = 5 x 101

Under what conditions will the reaction of graphite shown below be spontaneous? C (s) + 2Cl2 (g) → CCl4 (g); ΔH° = -106.7 kJ

Spontaneous only at low T (ΔS is negative (loss of gas), ΔH is negative, so ΔG = ΔH - TΔS will be negative only when T is small.)

If the reaction shown below is to be coupled to a second reaction in order to generate an overall spontaneous process, what must be true regarding this second reaction? Fe2O3 (s) → 2Fe (s) + 3232O2 (g); ΔG = 740.98 kJ

The free energy change must be more negative than -740.98 kJ. (When a large negative number is added to a positive number of lesser magnitude, the result is negative; the reaction will be spontaneous.)

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

The reaction becomes less spontaneous. (As Q increases, the reaction proceeds less spontaneously toward the products and ΔG becomes more positive.)

Consider the chemical reaction 2SO3 (g) → O2 (g) + 2SO2 (g), for which ΔH° = +198.4 kJ and ΔS° = +187.9 J/K. Which of the following statements correctly describe the effect of temperature on the spontaneity of this reaction?

The reaction will become more spontaneous as the temperature increases. The reaction is spontaneous only at higher temperatures.

In the human body, the oxidation of glucose produces sufficient free energy to drive the conversion of biomolecule ADP into ATP, a nonspontaneous process. This is an example of ______, where one step supplies enough free energy for another to occur.

coupling

The Gibbs ___ energy change (symbolized by Δ___) is a measure of the spontaneity of a process and of the useful energy available from it.

free, G

If a given process proceeds spontaneously toward the products, the value of the reaction quotient Q is _____ the equilibrium constant K and ΔG for the reaction will be _____.

less than; negative

If a given reversible reaction has positive values for both ΔH and ΔS, the value of ΔG will become _____ negative as temperature increases and the formation of the _____ will be increasingly favored.

more; products

The larger the equilibrium constant K for a reaction, the more _____ the value of ΔGo and the more the _____ are favored at equilibrium.

negative; products (If the value of K for a reaction is large, it means that the reaction favors the products strongly. The reaction is spontaneous in the forward direction, and the value of ΔGo will be negative)

The standard free energy change for a reaction is the free energy change for the reaction under ___-state conditions, which assumes that all gases are at ___ atm of pressure and all solutions have a concentration of ___ M.

standard, 1, 1

If the values of Q and K are very different If the values of Q and K are very similar

the magnitude of ΔG is large and the reaction can release a lot of free energy. the magnitude of ΔG is small and the reaction releases relatively little free energy.

ΔG is the maximum amount of useful _____ the system can possibly produce during a spontaneous process at constant T and P.

work

If the standard cell potential for a reaction is equal to 0 V, ΔG° is equal to ___ kJ.

zero

Consider the chemical reaction 2SO2 (g) + O2 (g) → 2SO3 (g), which has ΔH° = -198.4 kJ and ΔS° = -187.9 J/K. What is the value of ΔG°, and is the reaction spontaneous or nonspontaneous at 85°C?

ΔG = -131.1 kJ The reaction is spontaneous at this temperature. (ΔG = -198.4 kJ - 358 K(-187.9J/Kx1kJ1000)-187.9J/Kx1kJ1000 = -198.4 + 67.3 = -131.1 kJ)

Which of the following correctly describes the relationship between the free energy change, the reaction quotient, and the equilibrium constant?

ΔG = RT ln (Q/K)

Q = 1 Q < 1 Q > 1

ΔG = ΔG° ΔG < ΔG° ΔG > ΔG°

Which of the following is the correct form of the Gibbs equation for a process occurring at constant temperature?

ΔGsys = ΔHsys - TΔSsys

The molecular scene shows a gaseous equilibrium mixture at 460°C for the reaction of H2 (blue) and I2 (purple) to form HI according to the balanced equation H2 (g) + I2 (g) → 2HI (g). Each particle in the molecular scene represents 0.010 mol and the container volume is 1.0 L. Which statements correctly describe this system?

ΔG° = -23.8 kJ/mol Kc for the reaction = 50. (ΔG° = -RTln K = 8.314 × (460 + 273) × ln 50 = -23,800 J/mol = -23.8 kJ/mol Count the "particles" of each gas to determine the molar concentrations. Kc = [HI]2/[H2][I2] = (0.10)^2/(0.01)(0.02) = 50)

The molecular scene shows a gaseous equilibrium mixture at 298 K for the reaction of X into X2 according to the balanced equation 2X (g) → X2 (g). Each particle in the molecular scene represents 0.10 mol, and the container volume is 1.0 L. Which statements correctly describe this system? Select all that apply.

ΔG° = 0.55 kJ/mol Kc for the reaction = 0.80 The reaction is nonspontaneous as written. (Count the "particles" of each gas to determine the molar concentrations. Kc = [X2]/[X]^2 = 0.20/(0.50)^2 = 0.80 ΔG° = -RTln K = 8.314 × (298 K) × ln 0.80 = 550 J/mol = 0.55 kJ/mol)

A reaction is found to be spontaneous only at high temperatures. Which of the following must be true? Select all that apply.

ΔSorxn > 0 ΔHorxn > 0 (If the reaction is spontaneous only at high temperatures, it must be endothermic (ΔHorxn > 0) and ΔSorxn > 0.)

Which of the following values must be known in order to calculate the change in Gibbs free energy using the Gibbs equation?

ΔSsys ΔHsys T