Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

# Questions

### Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

1. The Ellingham diagram shows values of which thermodynamic quantity as a function of temperature?

 a Standard electrode voltage; b Standard free energy change of reaction; c Partial pressure of gas; d Enthalpy change of reaction.

2. For a closed system at equilibrium at a temperature T, which of the following statements are true?

1. ΔG = 0;
2. ΔG° = 0;
3. ΔH = TΔS;
4. ΔS = 0.

3. Why are the slopes of many of the lines on the Ellingham diagram almost identical?

 a Most reactions involve the elimination of one mole of gas, so there is a similar standard enthalpy change of reaction. b Most reactions involve the elimination of one mole of gas, so there is a similar standard entropy change of reaction. c The activity of most of the metals is the same. d The partial pressure of the reacting gas is the same for all reactions.

4. What thermodynamic quantity does the intercept at T=0 K for any standard free energy vs T line signify?

 a The approximate value of the standard entropy change; b The approximate value of the standard enthalpy change; c The equilibrium constant for the oxidation reaction; d Heat capacity of the oxide.

5. What is the decomposition temperature (to the nearest 50 K) for Ag2O? (This question should be completed with the help of the interactive Ellingham diagram included with this TLP).

 a 460 K b 500 K c 540 K d 620 K

6. What is the decomposition temperature (to the nearest 50 K) for PdO? (This question should be completed with the help of the interactive Ellingham diagram included with this TLP).

 a 1050 K b 1100 K c 1150 K d 1200 K

7. Which of the following elements can be used to produce Cr from Cr2O3 at 1200K? (This question should be completed with the help of the interactive Ellingham diagram included with this TLP).

1. Mg
2. Fe
3. Co
4. Al

8. Explain, using the Ellingham diagram, how a mixture of Cl2/O2 gas may be used to separate Zn from Fe in a galvanised scrap. (This question should be completed with the help of the interactive Ellingham diagram included with this TLP).