second law of thermodynamics

all spontaneous processes involve an increase in the entropy of the universe

standard entropy (S°)

entropy for one mole of a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K

standard entropy change (ΔS°)

change in entropy for a reaction calculated using the standard entropies

third law of thermodynamics

entropy of a perfect crystal at absolute zero (0 K) is zero

← Back to Chemistry 2e

Chemistry 2e · 16.3 The Second and Third Laws of Thermodynamics

The Second and Third Laws of Thermodynamics: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 21
Calculate $Δ S °$ for the following changes.
(a) $SnCl_{4} (l) ⟶ SnCl_{4} (g)$
(b) $CS_{2} (g) ⟶ CS_{2} (l)$
(c) $Cu (s) ⟶ Cu (g)$
(d) $H_{2} O (l) ⟶ H_{2} O (g)$
(e) $2 H_{2} (g) + O_{2} (g) ⟶ 2 H_{2} O (l)$
(f) $2 HCl (g) + Pb (s) ⟶ PbCl_{2} (s) + H_{2} (g)$
(g) $Zn (s) + CuSO_{4} (s) ⟶ Cu (s) + ZnSO_{4} (s)$
Sign up free to have it checked
Exercises 23
Determine the entropy change for the combustion of gaseous propane, C₃H₈, under the standard conditions to give gaseous carbon dioxide and water.
Sign up free to have it checked
Exercises 25
Using the relevant $S °$ values listed in Appendix G, calculate $Δ S °_{298}$
for the following changes:
(a) $N_{2} (g) + 3 H_{2} (g) ⟶ 2 NH_{3} (g)$
Sign up free to have it checked
Exercises 27
By calculating ΔS $_{u ni v}$ at each temperature, determine if the melting of 1 mole of NaCl(s) is spontaneous at 500 °C and at 700 °C.
$S_{NaCl (s)}^{^{\circ}} = 72.11 \frac{J}{mol\cdotK} S_{NaCl (l)}^{^{\circ}} = 95.06 \frac{J}{mol\cdotK} Δ H_{fusion}^{^{\circ}} = 27.95 kJ/mol$
Sign up free to have it checked
Exercises 29
Use the standard entropy data in Appendix G to determine the change in entropy for each of the following reactions. All the processes occur at the standard conditions and 25 °C.
(a) $C (s, graphite) + O_{2} (g) ⟶ CO_{2} (g)$
(b) $O_{2} (g) + N_{2} (g) ⟶ 2NO (g)$
Sign up free to have it checked

Key terms · 4

second law of thermodynamics: all spontaneous processes involve an increase in the entropy of the universe
standard entropy (S°): entropy for one mole of a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K
standard entropy change (ΔS°): change in entropy for a reaction calculated using the standard entropies
third law of thermodynamics: entropy of a perfect crystal at absolute zero (0 K) is zero

Learn 16.3 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 16.3 in the textbook · This section on openstax.org

The Second and Third Laws of Thermodynamics: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 21

Calculate $Δ S °$ for the following changes.

(a) $SnCl_{4} (l) ⟶ SnCl_{4} (g)$

(b) $CS_{2} (g) ⟶ CS_{2} (l)$

(d) $H_{2} O (l) ⟶ H_{2} O (g)$

(e) $2 H_{2} (g) + O_{2} (g) ⟶ 2 H_{2} O (l)$

(f) $2 HCl (g) + Pb (s) ⟶ PbCl_{2} (s) + H_{2} (g)$

(g) $Zn (s) + CuSO_{4} (s) ⟶ Cu (s) + ZnSO_{4} (s)$

Exercises 23

Determine the entropy change for the combustion of gaseous propane, C₃H₈, under the standard conditions to give gaseous carbon dioxide and water.

Exercises 25

Using the relevant $S °$ values listed in Appendix G, calculate $Δ S °_{298}$

for the following changes:

(a) $N_{2} (g) + 3 H_{2} (g) ⟶ 2 NH_{3} (g)$

Exercises 27

By calculating ΔS $_{u ni v}$ at each temperature, determine if the melting of 1 mole of NaCl(s) is spontaneous at 500 °C and at 700 °C.

$S_{NaCl (s)}^{^{\circ}} = 72.11 \frac{J}{mol\cdotK} S_{NaCl (l)}^{^{\circ}} = 95.06 \frac{J}{mol\cdotK} Δ H_{fusion}^{^{\circ}} = 27.95 kJ/mol$

Exercises 29

Use the standard entropy data in Appendix G to determine the change in entropy for each of the following reactions. All the processes occur at the standard conditions and 25 °C.

(a) $C (s, graphite) + O_{2} (g) ⟶ CO_{2} (g)$

(b) $O_{2} (g) + N_{2} (g) ⟶ 2NO (g)$

Key terms · 4

second law of thermodynamics: all spontaneous processes involve an increase in the entropy of the universe
standard entropy (S°): entropy for one mole of a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K
standard entropy change (ΔS°): change in entropy for a reaction calculated using the standard entropies
third law of thermodynamics: entropy of a perfect crystal at absolute zero (0 K) is zero

Learn 16.3 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 16.3 in the textbook · This section on openstax.org