20 Thermochemistry Practice Problems for DAT Exam Prep

V. Thermochemistry questions

Thermochemistry practice problems

There are a total of 11 phase change problems, which are important content-oriented in the summary part of this chapter. Click the ‘Answer’ button to see the corresponding answers and explanations, and click the ‘Go back’ button to slove the next questions.

THERMOCHEMISTRY TEST 1

1 / 20

When 75J of work is done on system, the ΔE is 100J. Which of the following is the correct statement about heat energy?

A. 25J of heat is absorbed into the system from its surroundings.

B. 25J of heat is released into the surroundings by the system.

C. 175J of heat is absorbed into the system from its surroundings.

D. 175J of heat is released into the surroundings by the system.

E. There is no change of the heat energy between system and its surroundings.

2 / 20

A cylinder is compressed from 5L to 3L volume by the pressure of 4 atm. How much work is done?

A. +8 atm·L

B. –8 atm·L

C. +12 atm·L

D. –12 atm·L

E. +20 atm·L

3 / 20

What is the work when water in a cylinder is evaporated and expanded from 10L to 15L against an external pressure of 3 atm?

A. + 1.67 atm·L

B. – 1.67 atm·L

C. +15 atm·L

D. –15 atm·L

E. – 45 atm·L

4 / 20

What is the mass of water when 420J of heat is used to raise the temperature from 30.0^oC to 35.0^oC? (Specific heat of water: 4.2 J/(g•^oC))

A. 5.0g

B. 10.0g

C. 15.0g

D. 20.0g

E. 25.0g

5 / 20

How much energy is required to raise the temperature of 45g of NaCl from 35.0^oC to 60.0^oC? (Specific heat of NaCl: 0.9 J/(g•^oC))

A. 135.0 J

B. 510.5 J

C. 1012.5 J

D. 1417.5 J

E. 2430.0 J

6 / 20

Which of the following applies the second law of thermodynamics?

A. Formation of liquid water from steam.

B. Producing sugar in a cell.

C. The sum of total energy from the system and its surroundings is unchanged.

D. Dissolution of NaCl in water.

E. Non-spontaneous process.

7 / 20

Which of the following applies to the positive change of enthalpy, +ΔH?

A. System gives off heat energy to its surroundings.

B. Reactants have higher energy than their products.

C. The heat of the surroundings is decreased.

D. The total energy is increased.

E. System becomes exothermic.


• System gives off energy to its surroundings. • System becomes exothermic. • The heat of the surroundings is increased. • Reactants have higher energy than products. • Total energy is not changed. • Ex/ State change: gas → liquid → solid	• System absorbs energy from its surroundings. • System becomes endothermic. • The heat of the surroundings is decreased. • Reactants have less energy than products. • Total energy is not changed. • Ex/ State change: solid → liquid → gas

8 / 20

Which of the following are NOT examples of exothermic processes?

A. Combustion of propane

B. Acid and base neutralization

C. Cold pack by chemical reaction of ammonium nitrate in water

D. Catabolism of glucose in a cell

E. Making ice from evaporated water

9 / 20

The combustion of acetylene, C₂H₂, with oxygen is gives off 1,255 kJ of heat energy in the following equation. How much heat is given off by the reaction of 2 moles of acetylene?

C₂H₂(g) + 5/2 O₂ (g) → H₂O(g) + 2CO₂(g) ΔH^o = -1,255 kJ

A. 627 kJ

B. 1,255 kJ

C. 2,510 kJ

D. 3,137 kJ

E. 3,525 kJ

10 / 20

How many grams of NH₃ is used when NH₃is reacted with excess O₂ and 150kJ of heat is released in the following reaction?

4NH₃(g) + O₂(g) → 2N₂H₄(l) + 2H₂O(l) ΔH = – 300 kJ

A. 4.3g

B. 8.5g

C. 17.0g

D. 34.0g

E. 68.0g

11 / 20

Calculate the energy change, DH, for the reaction 2A + B → 5D + 2E from the information in the table below.

A + B → 2C + D DH = + 100 kJ/mol

2D + E → ½ A + C DH = – 20 kJ/mol

A. +110kJ/mol

B. +80 kJ/mol

C. -80 kJ/mol

D. +140 kJ/mol

E. -140 kJ/mol

12 / 20

What is the correct equation of DH^o for the reaction 2CO(g) + O₂(g) → 2CO₂(g)?

2C(s) + O₂(g) → 2CO(g) ΔH₁

C(s) + O₂(g) → CO₂(g) ΔH₂

A. +ΔH₁ – 2ΔH₂

B. +ΔH₁ – ½ΔH₂

C. -2ΔH₁ + ΔH₂

D. -ΔH₁ + 2ΔH₂

E. – ½ΔH₁ + ΔH₂

13 / 20

A. 138.4 kJ

B. -138.4 kJ

C. -510.8 kJ

D. 510.8 kJ

E. -258.2 kJ

14 / 20

Calculate the enthalpy change from the reaction by using the table below.

A. -1600kJ

B. +5780kJ

C. +1600kJ

D. -5780kJ

E. +2080kJ

15 / 20

Choose the items that apply to positive entropy, +ΔS.

I. Dissolving solute in the solvent

II. Formation of glucose in the cells

III. CO(g) + 2H₂(g) → CH₃OH(l)

IV. C₄H₁₀(l) → C₄H₁₀(g)

A. I only

B. II and III

C. I and IV

D. I, II, and IV

E. II, III, and IV

16 / 20

Which of the following represents the greatest increasing entropy for the compound AB?

A. AB(s) → AB(g)

B. AB(g) → AB(g)

C. AB(g) → AB(l)

D. AB(g) → AB(s)

E. AB(s) → AB(l)

17 / 20

When a solute is dissolved in a solvent, the temperature of its system is increased. Which of the following applies to its surroundings?

A. ΔT<0, ΔS<0

B. ΔT>0, ΔS<0

C. ΔT0

D. ΔT>0, ΔS>0

E. ΔT=0, ΔS=0

18 / 20

Choose the items that apply to the spontaneous process.

I. Total energy is conserved.

II. Entropy is increased.

III. ΔG is negative

IV. ΔH is negative and ΔS is positive at T(K) > 0.

A. I and II

B. I, II, and III

C. I, II, and IV

D. II, III, and IV

E. All are correct

19 / 20

Which of the following is (are) correct statement(s)?

I. CH₃CH₂CH₂CH₃ has a greater standard molar entropy than CH₃CH₂CH₃ at the standard state.

II. Non-spontaneous reaction means ΔG > 0.

III. When ΔH > 0 and ΔS < 0 at T > 0, ΔG is always positive.

IV. The balance between spontaneous and non-spontaneous means ΔG = 0.

A. I and II

B. II and III

C. I, II, and III

D. I, II, and IV

E. All are correct.

20 / 20

What temperature is needed for a spontaneous reaction when ΔH is 5 kJ/mol and ΔS is 20 J/mol•K?

A. 230K

B. 235K

C. 240K

D. 245K

E. 255K

Your score is

The average score is 26%

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