Chem 1225 chapter 17
Which of the following reactions are predicted to have a positive value for ΔSrxn? Select all that apply.
N2O4(g) → 2NO2(g) H2CO3(aq) → H2O(l) + CO2(g)
As the reaction quotient Q increases, what is the effect on the spontaneity of the reaction?
The reaction becomes less spontaneous.
If the value of K for a given reaction is >> 1, then the value of ΔGo is
negative favors products
Calculate the entropy change of the surroundings in J/mol⋅K when 30 kJ of heat is released by the system at 27oC.
+100
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)?
1000yx1000yx
Calculate the value of ΔG for a reaction at 75oC whose enthalpy change is 50 kJ and whose entropy change is 100 J/K.
15.2 kJ
A chemist finds that the sublimation of a compound has a free-energy change of -2.5 kJ at 350oC, and a free-energy change of +0.5 kJ at 140oC. From this information, what is a likely value for the temperature of sublimation?
175oC
With reference to free-energy changes, the term "standard state" refers to a temperature of oC for all substances, a pressure of atm for gases, and a concentration of M for solutes. Express your answers as whole numbers without decimals.
25 1 1
A reaction is known to have ΔHo equal to -5 kJ and ΔSo equal to -100 J/K. What is the temperature (in K) at which this reaction becomes spontaneous?
50 K
Which of the following correctly describes the first law of thermodynamics?
Energy can be converted from one form to another, but it cannot be created or destroyed.
Which process below will result in an increase in the entropy of the system?
PCl5(g) → Cl2(g) + PCl3(g)
In order to calculate the entropy change of a reaction using tabulated values, which of the following are necessary? Select all that apply.
Standard entropies of all components of the reaction A balanced equation
Under equilibrium conditions, the equation ΔG = ΔGo + RT ln Q simplifies to which of the following?
ΔGo = -RT ln K
A reaction is found to be spontaneous only above a particular temperature. Which of the following must be true? Select all that apply.
ΔSorxn > 0 ΔHorxn > 0
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
What is the entropy change of the surroundings when 1.00 kg of ice (water) melts at 5oC? The molar enthalpy of fusion of water is 6.01 kJ/mol.
-1.20 × 103 J/K
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)
The value of ΔG for the Haber process, N2(g) + 3H2(g) → 2NH3(g), is -33.3 kJ at 25oC. Calculate the value of ΔH for the reaction, if the value of ΔS is -198 J/K.
-92.3 kJ
Which of the following statements correctly describe the effects of temperature on the spontaneity of a reaction? Select all that apply.
A reaction with a positive value of ΔS will become more spontaneous with increasing temperature. A reaction with a negative value of ΔS will become less spontaneous with increasing temperature.
Which statement correctly describes the relationship between the entropy and spontaneity of a process?
A reaction/process will be spontaneous if ΔSsys > 0 and ΔSsurr > 0.
For a chemical process, how is enthalpy change of the system (ΔHsys) related to the entropy change of the surroundings (ΔSsurr)?
An exothermic reaction will result in an increase in the entropy of the surroundings.
Which of the following options correctly describe the behavior of a reversible reaction for which both ΔH and ΔS < 0? Select all that apply.
At low temperatures, ΔGrxn < 0. The reaction will become less spontaneous as the temperature increases. The formation of the reactants will become increasingly favored as the temperature rises.
Which statements about the relationship between Q, K, and ΔG are correct? Select all that apply.
If Q is less than K, then the value of ΔG is less than zero. If Q is greater than K, then the value of ΔG will decrease as the reaction proceeds.
Which of the following statements are correct about the meaning of the signs of ΔG and ΔGo? Select all that apply.
If ΔG is negative, the reaction will occur spontaneously. If ΔGo is positive, the reaction favors reactants at equilibrium.
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply.
If ΔHsys is negative, ΔSsurr will be positive. ΔSsurr is inversely proportional to temperature.
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 surroundings?
Increase in ΔSsurr Increase in ΔSsys
Given the balanced chemical equation CH4(g) + 2O2(g) → CO2(g) + 2H2O(g), which of the following equations should be used to calculate the total entropy change for this reaction? (States of matter have been omitted for simplification.)
S[CO2] + 2(S[H2O]) - S[CH4] - 2(S[O2])
Under what conditions will the reaction of graphite shown below be spontaneous?
Spontaneous only at low T
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?
The free-energy change must be more negative than -740.98 kJ.
Which of the following options correctly defines the standard free-energy of formation for a substance?
The free-energy change that occurs when 1 mole of the compound is formed from its elements in their standard states
Which of the following options correctly explain the impact of ΔHsys on the entropy change of the surroundings? Select all that apply.
The lower the temperature, the greater the effect of ΔHsys on the entropy of the surroundings. At high temperature, the enthalpy change of the system will have a relatively small effect on the entropy of the surroundings.
Select which phase change, melting or vaporization, will have a greater increase in entropy for a given substance. In addition, select the statement(s) that explain(s) why.
The mobility of the particles increases much more when this phase change occurs. Vaporization of a substance
Consider the chemical reaction K+(aq) + OH-(aq) → KOH(s), for which ΔHo = +57.7 kJ/mol and ΔSo = -12.7 J/K. Which statement correctly describes the effect of temperature on the spontaneity of this reaction?
The reaction is not spontaneous under any temperature conditions.
The reaction 2NO2(g) → N2O4(g) has a ΔH value of -58.0 kJ and a ΔS value of -177 J/K. Select the statement that correctly describes the relationship between temperature and spontaneity for this reaction as written.
The reaction is spontaneous below 55oC.
Consider the chemical reaction 2SO3(g) → O2(g) + 2SO2(g), for which ΔHo = +198.4 kJ and ΔSo = +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.
Which of the following conditions are specified by standard state conditions? Select all that apply.
The standard state of an element is its most stable allotropic form at standard state temperature and pressure. Gases are at a pressure of 1 atm. Solutions are at a concentration of 1 M.
The value of ΔGo calculated using the equation ΔGo - TΔSo for temperatures other than 298 K is ______.
an estimate, because both ΔHo and ΔSo change with temperature
ΔH for the melting of ice is 6.01 kJ/mole, and the process is spontaneous at 25oC. Therefore the entropy change of the system must be ______.
greater than 20.2 J/mol⋅K
An exothermic reaction releases heat to the surroundings, causing a(n) _____ in the movement of the particles in the surroundings. The entropy of the surroundings will therefore _____.
increase; increase
When a reaction is at equilibrium, the reaction quotient Q is always equal to
k 0
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
When ΔG (the change in free energy) for a reaction is less than zero (negative), the reaction is _____ and the entropy change (ΔS) for the universe is _____.
spontaneous; positive
A given process will be spontaneous if the entropy change of the ______ for the process is greater than zero. Select all that apply
universe
Which of the following options correctly describe the free-energy change and spontaneity of the reaction Cu2O(s) → Cu(s) + 1212 O2(g) at 375 K if ΔH = 168 kJ/mol and ΔS = -9.63 J/K⋅mol? Select all that apply
ΔG = +172 kJ The reaction is not spontaneous at this temperature.
Which of the following statements correctly describe the standard free-energy of formation (ΔG0ff0) for a substance? Select all that apply.
ΔG0ff0 for any element in its most stable allotropic form at 1 atm is equal to zero. ΔG0ff0 is the free-energy change for the synthesis of 1 mole of a compound from its constituent elements in their standard states.
The equilibrium constant for the reaction shown below is 7 x 10-84. What information does this provide about the reaction? Select all that apply. H2(g) + I2(g) ⇌ 2HI(g)
ΔGo is positive for this reaction. At equilibrium the reaction mixture consists mostly of H2(g) and I2(g).
The reaction 4Fe(s) + 3O2(g) + 6H2O(l) → 4Fe(OH)3(s) is spontaneous at temperatures below 1950°C. If ΔH = -1582 kJ, calculate the entropy change for this reaction at 1950°C.
ΔS = -712 J/K
A reaction is found to be spontaneous only below a particular temperature. Which of the following must be true? Select all that apply.
ΔSorxn < 0 ΔHorxn < 0
