Chem Chapter 20
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)
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.
.01, .1 , 1
If we know that the entropy change for a reaction is x J/K and the system absorbed y kJ of heat during that reaction, what is the temperature at which this occurred (in K)?
1000y/x
sing the data provided in the table, calculate the equilibrium constant KP at 25oC for the reaction 2O3 (g) ⇌ 3O2 (g).
2.1 x 1057
Which of the following is an application of the second law of thermodynamics?
A gas expands because matter tends to spread out.
What effect does increasing the temperature of a gas have on its entropy, and why? Select all that apply.
As the temperature of a system is increased, all types of kinetic energies increase. The entropy of a system increases as the temperature increases.
In the expression ΔG = RT ln(QK)QK, ΔG = 1Blank 1Blank 1 1 , Incorrect Unavailable when Q is equal to K, i.e., when QKQK = 0Blank 2Blank 2 0 , Incorrect Unavailable.
Blank 1: 0 or zero Blank 2: 1 or one
In the expression ΔG = RT ln(QK)QK, ΔG = when Q is equal to K, i.e., when QKQK = .
Blank 1: 0 or zero Blank 2: 1 or one
Since entropy is typically tabulated in units of JBlank 1Blank 1 J , Correct Unavailable / K and standard enthalpies are typically tabulated in units of JBlank 2Blank 2 J , Incorrect Unavailable / mol, it is usually necessary to perform a unit conversion when using the formula ΔG = ΔH - TΔS to calculate the Gibbs free energy.
Blank 1: J or joules Blank 2: kJ or kilojoules
When a reaction is at equilibrium, the reaction quotient Q is always equal to 0Blank 1Blank 1 0 , Incorrect Unavailable and ΔG is equal to 1Blank 2Blank 2 1 , Incorrect Unavailable.
Blank 1: K, the equilibrium constant, or Keq Blank 2: 0 or zero
When a reaction is at equilibrium, the reaction quotient Q is always equal to and ΔG is equal to .
Blank 1: K, the equilibrium constant, or Keq Blank 2: 0 or zero
The standard free energy change for a reaction is the free energy change for the reaction under aBlank 1Blank 1 a , Incorrect Unavailable-state conditions, which assumes that all gases are at aaBlank 2Blank 2 aa , Incorrect Unavailable atm of pressure and all solutions have a concentration of aBlank 3Blank 3 a , Incorrect Unavailable M.
Blank 1: standard Blank 2: 1, one, or 1.0 Blank 3: 1, 1.0, or one
The combustion of glucose, represented by the equation C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (g), is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and its surroundings?
Increase in ΔSsys Increase in ΔSsurr
Which of the following statements correctly reflect the relationship between the spontaneity of a reaction and the sign of ΔH? Select all that apply.
It is possible for an exothermic process to be nonspontaneous. An endothermic process may be spontaneous under one set of conditions but nonspontaneous at a different temperature and pressure.
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? Select all that apply.
Kc for the reaction = 50. ΔG° = -23.8 kJ/mol
Which of the following is a correct description of the third law of thermodynamics?
The entropy of a perfect crystalline substance is 0 at 0 K.
As the reaction quotient Q increases, what is the effect on the spontaneity of the reaction?
The reaction becomes less spontaneous.
pic one
The reaction is nonspontaneous as written. Kc for the reaction = 0.80 ΔG° = 0.55 kJ/mol
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?
The reaction is spontaneous at this temperature. ΔG = -131.1 kJ
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? Select all that apply.
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
Under what conditions will the reaction of graphite shown below be spontaneous? C (s) + 2Cl2 (g) → CCl4 (g); ΔH° = -106.7 kJ
it is spont
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
How is the number of microstates in a system, W, related to the entropy of the system, S?
ln W ∝ S
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
Which of the following correctly describes the relationship between the free energy change, the reaction quotient, and the equilibrium constant?
ΔG = RT ln (QK)
Under standard-state conditions, the equation ΔG = RT ln(QKQK) simplifies to which of the following?
ΔG° = -RT ln(K)
When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflect this relationship (at constant pressure)?
ΔSsurr = - qsys/T ΔSsurr = - ΔHsys/T
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings? Multiple choice question. ΔSsurr > -ΔSsys
ΔSsurr > -ΔSsys
Calculate ΔSuniv and identify the process CO2 (g) → CO2 (aq) as spontaneous, nonspontaneous, or at equilibrium at 25oC. Use the values provided in the table below.
ΔSuniv = -27.2 J/mol⋅K The reaction is nonspontaneous at this temperature.
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
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
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply.
ΔSsurr is inversely proportional to temperature. If ΔHsys is negative, ΔSsurr will be positive.
