# Third Law of Thermodynamics & Entropy Changes (College)

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## Third Law of Thermodynamics & Entropy Changes

**Instructions:**
The following questions may require the use of a reference table. The questions concern the Third Law of Thermodynamics and calculating entropy changes in a reaction.

1.

Which of the following correctly classifies entropy?

- It is an intensive property, in that it depends on the identity of the substance
- It is an extensive property, in that it depends on the number of moles
- It is neither extensive nor intensive
- It is an extensive property, in that it depends on the identity of the substance

2.

Which of the following correctly represents trends in Sº, in going from [math]H_2O(s)[/math] to [math]H_2O(l)[/math]?

- A decrease
- An increase
- A decrease, and an increase
- No changes

3.

Which of the following represents the value for the entropy of a perfect crystal at 0 K?

- Positive
- Negative
- 0
- 1

4.

Which of the following accounts for the entropy value of a perfect crystal at 0 K?

- All of the particles are arranged in a regular pattern
- All of the particles are arranged in a perfect position in the lattice structure
- All of the particles move past one another with minimal entropy
- All of the particles are evenly dispersed

5.

Which of the following factors dominates changes in positional entropy for particles in a reaction, when gaseous reactants and products are involved?

- The temperature of the particles
- The volume of the particles
- The physical states of the particles themselves
- The numbers of gaseous reactants and products

6.

For reactants involving gas molecules, which of the following conditions need to be constant, in order to determine changes in positional entropy?

- Temperature, only
- Pressure, only
- Temperature and Pressure, only
- Volume, only

7.

Which of the following reactions correctly demonstrates an increase in positional entropy?

- [math]2H_2 (g) + O_2 (g) rarr 2H_2O(l)[/math]
- [math]N_2(g) + O_2(g) rarr 2NO(g)[/math]
- [math]N_2O_4(g) rarr 2NO_2(g)[/math]
- None of the above

8.

Which of the following represents an increase in positional entropy?

- [math]2CO(g) + O_2(g) rarr 2CO_2(g)[/math]
- [math]2C_2H_6(g) + 7O_2(g) rarr 4CO_2(g) + 6H_2O(g)[/math]
- [math]N_2(g) + O_2(g) rarr 2NO(g)[/math]
- None of the above

9.

Which of the following can be used to calculate entropy changes in reactions?

- [math]∆Gº_{reaction}=∑n_{r}∆Gº_f{"reactants"}-∑n_{p}∆Gº_f{"products"}[/math]
- [math]∆Gº_{reaction}=∑n_{r}∆Gº_f{"reactants"}+∑n_{p}∆Gº_f{"products"}[/math]
- [math]∆Gº_{reaction}=∑n_{p}∆Gº_f{"products"}-∑n_{r}∆Gº_f{"reactants"}[/math]
- None of the above

10.

Based on the following reaction:

[math]SO_3(s) rarr SO_3(l)[/math]

What is the value of [math]∆Sº_{reaction}[/math]? Show your work.

[math]SO_3(s) rarr SO_3(l)[/math]

What is the value of [math]∆Sº_{reaction}[/math]? Show your work.

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