Free Printable AP Chem Thermodynamics Practice

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AP Chem Thermodynamics Practice

Total questions: 81

Worksheet time: 59mins

Name

Class

Date

Entropy is a measure of the number of possible ways that the energy of a system can be distributed.

True

False

ΔH value in an endothermic reaction is a positive number.

True

False

Which phase of matter has the greatest motion and the least orderly arrangement?

solid

liquid

gas

True/False: The rate of a chemical reaction is unrelated to the spontaneity of the reaction.

True

False

For which of these processes is the value of ΔH expected to be positive?

The temperature increases when calcium chloride dissolves in water.

Steam condenses to liquid water

Dry ice sublimates

The reaction ½ A₂ + 2 B₂ + C ⟶ CAB₄ has an enthalpy of formation of -104 kJ and a change in entropy of -60.8 J/K at 30 °C. Calculate the value of Gibb's free energy and state whether the reaction is thermodynamically favorable (i.e., spontaneous) at these conditions.

-85.6 kJ, thermodynamically favorable

-18.3 kJ, not thermodynamically favorable

+18.3 kJ, thermodynamically favorable

+85.6 kJ, not thermodynamically favorable

For which of the following processes would ΔS have a negative value (look at the states s, l, or g) ?

2Fe₂O₃ (s) → 4Fe(s)+3O₂(g)

H₂(g) + C₂H₄(g) → 3C₂H₆(g)

Mg²⁺(aq)+2OH^-(aq) → Mg(OH)₂(s)

NH₃(g) + 2CH₄(g) + 5/2 O₂(g) → H₂NCH₂COOH(s) + 3H₂O(l)... At constant temp, ΔS is...

increasing

decreasing

staying the same

speeding up

What is the equation for Gibbs Free Energy?

ΔG = ΔH + TΔS

ΔH = ΔG - TΔS

ΔS = ΔH - TΔG

ΔG = ΔH - TΔS

10.

A process will be spontaneous when the change in free energy is...

zero

positive

negative

11.

Free energy change at equilibrium is...

Zero

Positive

Negative

12.

Which combination of ΔH and ΔS will never be thermodynamically favorable at any temperature?

+ΔH and +ΔS

+ΔH and -ΔS

-ΔH and -ΔS

-ΔH and +ΔS

13.

1. Given the following information, calculate ΔG⁰ for the reaction below at 25⁰C:

SnCl₄(l) + 2 H₂0(l) → SnO₂(S) + 4HCl(g),

ΔH⁰=+133.0 kJ and ΔS⁰ =+401.5 J/K

-252.6 kJ

-13.4 kJ

13.4 kJ

252.6 kJ

14.

When a reaction is exothermic and the products have more entropy than the reactants, the reaction is

thermodynamically favorable, with a negative ΔG

thermodynamically favorable, with a positive ΔG

not thermodynamically favorable, with a negative ΔG

thermodynamically favorable, with a positive ΔG

15.

16.

Given the balanced equation:

I₂(s) + energy ⟶ I₂(g)

As a sample of solid iodine sublimes, the entropy of the sample

increases because the particles are less randomly arranged

increases because the particles are more randomly arranged

decreases because the particles are less randomly arranged

decreases because the particles are more randomly arranged

17.

18.

19.

A reaction that is spontaneous at any temperature has a

______ entropy change and a ____ enthalpy change.

positive, positive

positive, negative

negative, negative

negative, positive

20.

A reaction that is spontaneous at low temperatures only has a ____ entropy change and a _____ enthalpy change.

positive, positive

positive, negative

negative, negative

negative, positive

21.

A reaction that is thermodynamically favorable at high temperatures but not thermodynamically favorable at low temperatures has a ____ entropy change and a ____ enthalpy change.

positive, positive

positive, negative

negative, negative

negative, positive

22.

A reaction that is not thermodynamically favorable at any temperature has a

____ entropy change and a ____ enthalpy change.

positive, positive

positive, negative

negative, negative

negative, positive

23.

Calculate the standard entropy change for the following reaction:

Cu(s)+1/2 O₂(g) → CuO(s).

Given that

S⁰ (Cu(s)) = 33.15 J/K*mol

S⁰ (O₂(g)) = 205.14 J/K*mol

S⁰ (CuO(s)) = 42.5 J/K*mol

195.66 J/K.mol

93.09 J/K.mol

-93.09 J/K.mol

+195.66 J/K.mol

24.

Given the following information, calculate ΔG⁰ for the reaction below at 25⁰C:

SnCl₄(l) + 2 H₂0(l) → SnO₂(S) + 4HCl(g),

ΔH⁰=133.0 kJ and ΔS⁰ =401.5 J/K

-252.6 kJ

-13.4 kJ

13.4 kJ

252.6 kJ

25.

Given the following information, calculate ΔG⁰for the following reaction below at 25⁰C: 2H₂O₂(l) →2H₂O(l) + O₂(l)

if the equilibrium constant K_c = 8.52 x 10⁴⁰

-37700 kJ

-342.6 kJ

+233.5 kJ

-233.5 kJ

26.

If ΔH and ΔS are both negative , then the sign of ΔG is ____.

positive

negative

indeterminate

27.

Calculate the temperature at which a given reaction would become spontaneous if ΔH =+119kJ and ΔS=+263J/(K mol)

452 K

2210 K

382 K

363 K

28.

Which process is accompanied by a decrease in entropy?

boiling of water

condensing of water vapor

subliming of iodine

melting of ice

29.

Systems in nature tend to undergo changes toward

lower energy and less disorder

lower energy and more disorder

higher energy and less disorder

higher energy and more disorder

30.

Thermodynamically favorable reactions are driven by

increasing enthalpy and increasing entropy.

decreasing enthalpy and decreasing entropy.

increasing enthalpy and decreasing entropy.

decreasing enthalpy and increasing entropy.

31.

Solid magnesium dissolves in a hydrochloric acid, releasing hydrogen gas and heat from a solution of magnesium chloride. What is the sign of ΔH for this reaction?

Negative because it is exothermic

Negative because it is endothermic

Positive because it is exothermic

Positive because it is endothermic

32.

Solid magnesium dissolves in a hydrochloric acid, releasing hydrogen gas and heat from a solution of magnesium chloride. What is the sign on ΔS for this reaction?

Negative because it is becoming more ordered.

Negative because it is becoming more disordered.

Positive because it is becoming more ordered.

Positive because it is becoming more disordered.

33.

A reaction has a positive ΔH and a positive ΔS. Which of the following is true?

It will be spontaneous at all temperatures.

It will be nonspontaneous at all temperatures.

It will be spontaneous at low temperatures.

It will be spontaneous at high temperatures.

34.

Entropy increases from solid, liquid to gas. Why?

Molecular disorder increases

Molecular randomness decreases

Molecules are more energetic

Molecules are more reactive

35.

Identify whether the following results in an increase or decrease in entropy:

3 moles of gas (on reactant side) ⟶ 6 moles of gas (product)

increase

decrease

no change

36.

Which reaction has the greatest increase in entropy?

2H₂0 (l) ⟶ 2H_{2 (g)} + O_{2 (g)}

2H₂O(g) ⟶2H₂(g) + O₂(g)

H₂O(g) ⟶ H₂O(l)

H₂O(l) ⟶ H₂O(s)

37.

Given the change of phase:

CO₂(g) ⟶ CO₂(s)

As CO₂(g) changes to CO₂(s), the entropy of the system ____.

decreases

increases

remains the same

38.

Solid magnesium dissolves in a solution of hydrochloric acid, releasing hydrogen gas, and the temperature of the contents of the baker increases. What is the sign on ΔG for this reaction?

Negative because it is spontaneous

Negative because it is nonspontaneous

Positive because it is spontaneous

Positive because it is nonspontaneous

39.

What signs of Δ H and Δ S will always yield a reaction that is spontaneous ?

Δ H = + Δ S = +

Δ H = - Δ S = -

Δ H = - Δ S = +

Δ H = + Δ S = --

40.

As NaCl dissolves according to the equation NaCl(s) → Na⁺(aq) + Cl^-(aq), the entropy of the system

Increases

Decreases

Remains the same

41.

Predict the entropy change, ΔS.

ΔS = +

ΔS = -

ΔS = 0

ΔS = no change

42.

Thermodynamically favorable reactions tend to go to...

low energy and high entropy

low energy and low entropy

high energy and high entropy

high energy and low entropy

43.

In which case is a reaction spontaneous at all temperatures?

ΔH is positive, ΔS is positive

ΔH = 0, ΔS is negative

ΔS = 0, ΔH is negative

ΔH is negative, ΔS is negative

44.

Thermodynamically unfavorable reactions...

are very slow

occur only with a sustained energy input

occur without any additional assistance

are always exothermic

are very fast

45.

When ammonium nitrate dissolves in water, the solution gets cold. Which is true?

Reaction is ENDOTHERMIC with positive ΔH

Reaction is ENDOTHERMIC with -ΔH

Reaction is EXOTHERMIC with a -ΔH

Reaction is EXOTHERMIC with +ΔH

46.

For the reaction C₂H₆ (g) ⟶ C₂H₄ (g) + H₂ (g)

ΔH^ο is +137 kJ/mol and ΔS^οis +120 J/K mol. This reaction is:

nonspontaneous at all temperatures

proceeding at a rapid rate

spontaneous only at high temperatures

spontaneous at all temperatures

spontaneous only at low temperature

47.

A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if ΔH is __________ and ΔS is __________.

+, +

-, -

+, -

-, +

+, 0

48.

For a reaction to be spontaneous under standard conditions at all temperatures, the signs of ΔH^Ο and ΔS^Ο must be __________ and __________, respectively.

+, +

+, -

-, +

-, -

+, 0

49.

Calculate ∆G and state if the process is spontaneous or nonspontaneous using the following information:

∆H_system = 145 kJ, T = 293 K, ∆S_system = 192 J/K

-56111 kJ/mol ; nonspontaneous

-56111 kJ/mol ; spontaneous

89 kJ/mol ; spontaneous

89 kJ/mol ; nonspontaneous

50.

Calculate ∆G and state if the process is spontaneous or nonspontaneous

∆H_system = -15.9 kJ, T = 373 K, ∆S_system = -268 J/K

99964 kJ/mol ; nonspontaneous

84 kJ/mol ; nonspontaneous

84 kJ/mol ; spontaneous

99964 kJ/mol ; spontaneous

51.

Under certain conditions, iron ore (Fe₃O₄) can be converted to iron for the following reaction:

Fe₃O₄(s) + 4 H₂(g) → 3 Fe(s) + 4 H₂O(g).

∆H = 149.8 kJ and ∆S = 6100 J/K.

Is the reaction thermodynamically favorable at 298 K?

Yes, because ΔG < 0

Yes, because ΔG > 0

No, because ΔG < 0

No, because ΔG > 0

52.

Which of the following statements describes a system with Keq < 1 ?

There are more products than reactants when the reaction reached equilibrium.

There are more reactant than products when the reaction reached equilibrium.

The amount of reactants is equal to the amount of products.

53.

Which of the following statements describes a system with K_eq > 1 ?

There are more products than reactants when the reaction reached equilibrium.

There are more reactant than products when the reaction reached equilibrium.

The amount of reactants is equal to the amount of products.

ΔG < 0

ΔG > 0

54.

The value of K_eq for a particular system at equilibrium is known to be 340 at 23 °C. This means...

...the reaction is thermodynamically favorable in the forward direction.

...the reaction is thermodynamically favorable in the reverse direction.

...the reaction is not thermodynamically favorable in any direction.

thermodynamic favorability cannot be determined from this data.

55.

The value of K_eq for a particular system at equilibrium is known to be 2.45x10^-13at 23 °C. This means...

...the reaction is thermodynamically favorable in the forward direction.

...the reaction is thermodynamically favorable in the reverse direction.

...the reaction is not thermodynamically favorable in any direction.

thermodynamic favorability cannot be determined from this data.

56.

A nonspontaneous reaction...

...will be product favored at equilibrium.

...will not favor the reactants nor the products at equilibrium.

...will be reactant favored at equilibrium.

...will not require energy in order to occur.

57.

For the reaction 2NO (g) $\longleftrightarrow$ N₂ (g) + O₂ (g) has a K = 1.0x10³¹.

Which statement is correct?

The reaction has $\Delta G$ < 0 since the K value is very large. The reaction must be exothermic since the $\Delta S$ is very small and will not affect the value for $\Delta G$

The reaction has $\Delta G$ < 0 since the K value is very large. The reaction must be exothermic since the value for $\Delta S$ is very large

The reaction has $\Delta G$ >0 since the K value is very large. The reaction must be endothermic since the value for $\Delta S$ is close to zero and will not affect the value for $\Delta G$

58.

Calculate the value of ΔG° at 298 K if the equilibrium constant is equal to 24.29. (Hint: R=8.314 J mol^-1 K^-1)

7903 kJ/mol

-7903 kJ/mol

7.903 kJ/mol

-7.903 kJ/mol

59.

The entropy will usually increase when

a molecule is broken into two or more smaller molecules

a reaction occurs that results in an increase in the number of moles of gas

a solid changes to a liquid

all of these

60.

Which reaction has a +ΔS ?

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

H₂O(g) + CO₂(g) → H₂CO₃(aq)

H₂(g) + I₂(g) → 2Hl(g)

C₂H₂O₂(g) → 2CO(g) + H₂(g)

61.

Consider a reaction with ΔHrxn = -77.91 kJ/mol and ΔSrxn = -0.4211 kJ/mol. At what temperature will the reaction switch between nonspontaneous and spontaneous?

(a)

62.

Consider a reaction with ΔHrxn = 90.84 kJ/mol and ΔSrxn = 0.1082 kJ/mol. At what temperature will the reaction switch between nonspontaneous and spontaneous?

839.6 K

816.2 K

848.99 K

16 K

63.

K = 13.2 for a reaction at 25°C. What is ΔG?

(Include units with your answer: ex. +4500 J/mol or +4.5 kJ/mol)

(a)

64.

For a reaction at 25°C, ΔG = -28.0 kJ/mol. What is K?

1.011

1.111

0.805

8.1 x 10⁴

65.

When ΔG is negative, a process is thermodynamically favorable.

True

False

66.

A reaction has both positive ∆S° and ∆H° values. From this information alone, you can conclude that the reaction

is thermodynamically favorable at any temperature.

is not thermodynamically favorable at high temperatures.

can be thermodynamically favorable only at low temperatures.

can be thermodynamically favorable only at high temperatures.

67.

Which of the following is not expected to have a value of zero at 25°C and 1 atm?

∆H°_f for F_{2 (g)}

∆G°_ffor Li_(s)

S° for Fe_(s)

∆H°_f for Mg_(s)

68.

A certain non-spontaneous reaction has ∆H of 12.3 kJ and a ∆S of 42 J/K. At approximately what temperature would the reaction become spontaneous?

-20°C

0°C

20°C

100°C

69.

A student volunteers to bring ice tea to a class picnic. She boils water to which she has added tea bags. Time is running short, so she places hot tea into an insulated, steel container, adds some ice cubes then seals the container. Assume that there is no heat exchange with the surroundings. Which of the following would be true?

The total energy and entropy both remain the same.

The total energy decreases while the entropy increases.

The total energy and entropy decreases.

None of the above.

70.

Which of the following is true when ice melts?

∆H<0 ∆S<0

∆H=0 ∆S=0

∆H<0 ∆S>0

∆H>0 ∆S>0

71.

Which of the following is true for the condensation of benzene, C₆H₆?

∆H°>0, ∆S°>0

∆H°>0, ∆S°<0

∆H°<0, ∆S°>0

∆H°<0, ∆S°<0

72.

At a certain temperature C_(s) + O_{2 (g)} ⟶ CO_{2 (g)}has a ∆G of -339.4 kJ. This means that at this temperature

the system is at equilibrium.

gaseous carbon dioxide is unstable.

gaseous carbon dioxide spontaneously forms.

this system has a high reaction rate.

K > 1

73.

When propane burns in air, heat is released:

C₃H_{8 (g)} + 5O_{2 (g)} ⟶ 3CO_{2 (g}) + 4H₂O_(g)

What are the signs of ∆H, ∆S, and ∆G for this process?

∆H<0 ∆S>0 ∆G>0

∆H<0 ∆S>0 ∆G<0

∆H<0 ∆S<0 ∆G<0

∆H<0 ∆S<0 ∆G>0

74.

It is observed that the reaction producing KCl from its elements goes essentially to completion. Which of the following statements must be true about the thermodynamic favorability of the reaction?

K(s) + 1/2 Cl₂(g) ⟶ KCl(s)

The reaction is favorable and enthalpy-driven.

The reaction is favorable and entropy-driven.

The reaction is favorable and driven by both the enthalpy and entropy changes.

The reaction is unfavorable due to unfavorable changes in enthalpy and entropy.

75.

Given the data included, what is the Gibbs free energy change for the reaction:

2SO_{2 (g)} + O_{2( g)} → 2SO_{3 (g)}

-70.0 kJ

+70.0 kJ

+140.0 kJ

-140.0 kJ

76.

If ΔH and ΔS are both positive , then the sign of ΔG is ____.

positive

negative

indeterminate

77.

Given the following information, calculate K_c for the reaction below at 25⁰C:

SnCl₄(l) + 2 H₂0(l) → SnO₂(S) + 4HCl(g),

ΔG⁰=13.4 kJ

(a)

78.

When ΔG is negative, a process has a K_eq < 1

True

False

79.

When ΔG is positive, a process has a K_eq < 1

True

False

80.

Given the following information, calculate K_c for the reaction below at 25⁰C:

SnO₂(S) + 4HCl(g), → SnCl₄(l) + 2 H₂0(l)

ΔG⁰=-13.4 kJ

However, no products are observed when the tin(IV) oxide and hydrochloric acid are combined. Which of the following explains this reaction?

The entropy change for the reaction is negative

The reaction has a very large activation energy

The reaction is not thermodynamically favorable

The enthalpy change for the reaction is a large, positive value

81.

Under certain conditions, iron ore (Fe₃O₄) can be converted to iron for the following reaction:

Fe₃O₄(s) + 4 H₂(g) → 3 Fe(s) + 4 H₂O(g).

∆H = 149.8 kJ and ∆S = 6100 J/K.

However, at 25^oC, the formation of iron metal is found to proceed very slowly. Which of the following statements is consistent with this information?

The reaction is thermodynamically favorable, but the reaction has a large activation energy

The reaction is thermodynamically favorable, but the reaction has a small activation energy

The reaction is not thermodynamically favorable, but the reaction has a large activation energy

The reaction is not thermodynamically favorable, but the reaction has a small activation energy

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AP Chem Thermodynamics Practice

Total questions: 81

Worksheet time: 59mins

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