Gen Chem Ch 17

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)

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

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

1; 1

In order to calculate the entropy change of a reaction using tabulated values, which of the following are necessary? Select all that apply.

A balanced equation Standard entropies of all components of the reaction

Which of the following is an application of the second law of thermodynamics?

A gas expands because matter tends to spread out.

What is a spontaneous process?

A process that occurs under specified conditions without a continuous input of energy

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.

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 correctly describes the first law of thermodynamics?

Energy can be converted from one form to another, but it cannot be created or destroyed.

True or false: For an element in its standard state, the standard entropy So is equal to 0 J/mol⋅K.

False

Which statements about the relationship between Q, K, and ΔG are correct? Select all that apply.

If Q is greater than K, then the value of ΔG will decrease as the reaction proceeds. If Q is less than K, then the value of ΔG is less than zero.

Which of the following statements are correct about the meaning of the signs of ΔG and ΔGo? Select all that apply

If ΔGo is positive, the reaction favors reactants at equilibrium. If ΔG is negative, the reaction will occur spontaneously.

Since entropy is typically tabulated in units of ______ / mol⋅K and standard enthalpies are typically tabulated in units of ______ / mol, it is usually necessary to perform a unit conversion when calculating Gibbs free energy.

J; kJ

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])

Which changes in state will result in an increase in the entropy of a substance? Select all that apply.

Solid to vapor Liquid to vapor Solid to liquid

Which of the following statements correctly explain the increase in entropy that occurs when a substance changes from a solid to liquid, or liquid to gas? Select all that apply.

The energy of the particles increases during these phase changes. The freedom of movement of the particles increases in the change solid → liquid → gas.

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.

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) → 2 Fe(s) + 3/2 O2(g); ΔG = 740.98 kJ

The free-energy change must be more negative than -740.98 kJ.

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.

Which of the following options correctly describe standard entropy? Select all that apply.

The units of standard entropy are J/mol⋅K. The standard entropy of a substance is its absolute entropy at 1 atm.

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.

Vaporization of a substance The mobility of the particles increases much more when this phase change occurs.

The third law of thermodynamics states that a perfect ______ of a pure solid substance has ______ entropy at a temperature of 0 K.

crystal; zero/no

The first law of thermodynamics states that _____ is always conserved.

energy

In order to predict whether the reaction below will be spontaneous under a given set of conditions, the change in both ______ and ______ for the process under those conditions must be known. N2(g) + 3H2(g) → 2NH3(g)

enthalpy; entropy

The second law of thermodynamics states that the total _____ of the universe will _____ for any spontaneous process.

entropy; increase

The entropy change for a process is calculated from the equation ΔS = S______ - S______.

final; initial

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

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

The change in entropy for a given process can be calculated by subtracting the ______ entropy of the system from the ______ entropy of the system.

initial/starting; final/ending

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

In order for the products to be favored in a reaction, the value of the standard free-energy change (ΔGo) must be _____.

negative

A spontaneous process ______.

occurs under a given set of conditions

For a chemical reaction, ΔSorxn = ΣnSo(______) - ΣnSo(______).

products/final; reactants/initial

A reaction with a positive value of ΔGo will favor ______ at equilibrium, while a reaction with a negative value of ΔGo will favor ______ at equilibrium.

reactants; products

The ______ law of thermodynamics states that a spontaneous process will result in an increase in the entropy of the universe.

second

The ______ entropy of a substance is its absolute entropy at 1 atm

standard

The Gibbs free energy change ΔG allows us to determine the spontaneity of a process based on thermodynamic changes to the ______.

system only

The sign of which quantity indicates whether or not a particular reaction or process will occur spontaneously?

ΔG

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

ΔG°rxn

The reaction is spontaneous only at low T if

ΔH < 0 and ΔS < 0

The reaction is always spontaneous if

ΔH < 0 and ΔS > 0

The reaction is always nonspontaneous if

ΔH > 0 and ΔS < 0.

The reaction is spontaneous only at high T if

ΔH > 0 and ΔS > 0.

A reaction is found to be spontaneous only above a particular temperature. Which of the following must be true? Select all that apply.

ΔHorxn > 0 ΔSorxn > 0

Which of the following options correctly show how to calculate the entropy change of a system? Select all that apply.

ΔS = Sf - Si ΔS = k ln Wf/Wi

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