20.1. Entropy http://www.ck12.org
Problems
- Predict the sign of∆S for each of the following reactions. Explain your reasoning.
a. 4Na(s) + O 2 (g)→2Na 2 O(s)
b. Zn(s) + 2H+(aq)→Zn^2 +(aq) + H 2 (g)
c. 2C 2 H 6 (g) + 7O 2 (g)→4CO 2 (g) + 6H 2 O(g)
d. H 2 (g) + F 2 (g)→2HF(g) - Use the standard entropies listed below to calculate the standard entropy change (∆S°) for each of the reactions
in problem number 6.
a. Na(s) = 51.05 J/K•mol; O 2 (g) = 205.0 J/K•mol; Na 2 O(s) = 72.8 J/K•mol
b. Zn(s) = 41.6 J/K•mol; H+(aq) = 0; Zn^2 +(aq) = 106.5 J/K•mol; H 2 (g) = 131.0 J/K•mol
c. C 2 H 6 (g) = 229.5 J/K•mol; O 2 (g) = 205.0 J/K•mol; CO 2 (g) = 213.6 J/K•mol; H 2 O(g) = 188.7 J/K•mol
d. H 2 (g) = 131.0 J/K•mol; F 2 (g) = 203.3 J/K•mol; HF(g) = 173.5 J/K•mol
Further Reading / Supplemental Links
- Entropy, http://www.kentchemistry.com/links/Kinetics/entropy.htm
- AllAboutEntropy,TheLawsofThermodynamics,andOrderfromDisorder, http://www.entropylaw.com/
Points to Consider
The drives toward lower enthalpy and greater entropy determine whether a chemical reaction is likely to occur under
a given set of conditions.
- How can enthalpy and entropy changes be combined into one quantity?
- If a reaction is not spontaneous under one set of conditions, is it possible that it will be spontaneous under
some other set of conditions?