Question 1

Which of the following substances has the greatest standard molar entropy ($$S^\circ) at 25$$°C and 1 atm?

Accepted Answer

$$\mathrm{He(g)}$$

Question 2

Which of the following has the lowest standard molar entropy ($$S^\circ$$)?

Accepted Answer

$$\mathrm{H_2O(s)}$$

Question 3

Which reaction below results in a positive entropy change for the system ($$\Delta S_{sys} \u003e 0$$)?

Accepted Answer

$$\mathrm{C_2H_2O_2(g) \rightarrow 2CO(g) + H_2$(g)}$$

Question 4

Which of the following reactions results in a negative entropy change for the system ($$\Delta S_{sys} \u003c 0$$)?

Accepted Answer

$$\mathrm{H_2O(g) \rightarrow H_2O(s)}$$

Question 5

Which process leads to a positive change in the entropy of the system?

Accepted Answer

Helium gas escapes from the hole in a balloon.

Question 6

Which of the following processes will lead to a decrease in the entropy of the system?

Accepted Answer

Iron and oxygen react to form rust.

Question 7

Calculate $$\Delta S$$ for the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightarrow 2HI(g)}$$ given the following standard molar entropies:

$$S^\circ(\mathrm{H_2$(g)}) = 130.58\ \mathrm{J/(mol\cdot K)}$$ 
$$S^\circ(\mathrm{I_2$(g)}) = 116.73\ \mathrm{J/(mol\cdot K)}$$ 
$$S^\circ(\mathrm{HI(g)}) = 206.3\ \mathrm{J/(mol\cdot K)}$$

Accepted Answer

$$+165.29\ \mathrm{J/(mol\cdot K)}$$

Question 8

If $$3.500\ \mathrm{g} of Ni$$ ($$58.69\ \mathrm{g/mol}) $$are reacted with excess oxygen to form nickel(II) oxide under standard state conditions, what is the entropy change for the reaction?

$$2\mathrm{Ni(s)} + \mathrm{O_2$(g)} \rightarrow 2\mathrm{NiO(s)}$$

Given: $$S^\circ(\mathrm{Ni}) = 182.1\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{O_2$}) = 205.0\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{NiO}) = 37.99\ \mathrm{J/(mol\cdot K)}$$

Accepted Answer

$$-24.7\ \mathrm{J/K}$$

Question 9

What is the entropy change if $$4.500\ \mathrm{g} of$$ $$\mathrm{$$CaCO_3$$(s)} is $$placed in a container and allowed to decompose to $$\mathrm{CaO(s)}$$ and $$\mathrm{CO_2$(g)}$$?

$$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$

Given: $$S^\circ(\mathrm{$$CaCO_3$$}) = 92.88\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{CaO}) = 39.75\ \mathrm{J/(mol\cdot K)}$$, $$S^\circ(\mathrm{CO_2$}) = 213.6\ \mathrm{J/(mol\cdot K)}$$

Accepted Answer

$$+35.7\ \mathrm{J/K}$$

Question 10

Processes are always spontaneous, regardless of temperature, when which of the following is true (for the system)?

Accepted Answer

$$\Delta H  0$$

Question 11

What is the standard Gibbs free energy change ($$\Delta G_{rxn}) $$for the reaction:

$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}$$

Given: $$\Delta G^\circ_f(\mathrm{CH_4$(g)}) = 50.8\ \mathrm{kJ/mol}$$, $$\Delta G^\circ_f(\mathrm{CO_2$(g)}) = -394.4\ \mathrm{kJ/mol}$$, $$\Delta G^\circ_f(\mathrm{H_2O(g)}) = -228.57\ \mathrm{kJ/mol}$$

Accepted Answer

$$-751\ \mathrm{kJ/mol}$$

Question 12

Hydrogen reacts with nitrogen to form ammonia according to:

$$3\mathrm{H_2$(g)} + \mathrm{N_2$(g)} \rightarrow 2\mathrm{NH_3$(g)}$$

Given $$\Delta H^\circ = -92.38\ \mathrm{kJ/mol}$$ and $$\Delta S^\circ = -198.2\ \mathrm{J/(mol\cdot K)}$$, determine $$\Delta G^\circ at$$ $$25^\circ\mathrm{C}.$$

Accepted Answer

$$-33.32\ \mathrm{kJ/mol}$$

Question 13

A reaction has a low enthalpy of reaction value and is not spontaneous at low temperature but becomes spontaneous at high temperature. What are the signs for $$\Delta H^\circ$$ and $$\Delta S^\circ$$, respectively?

Accepted Answer

Positive, Positive

Question 14

Which of the following best explains why the entropy of $$\mathrm{H_2O(l)} is $$less than that of $$\mathrm{H_2O(g)} at $$the same temperature?

Accepted Answer

Liquid water molecules are more ordered due to hydrogen bonding.

Question 15

Which of the following real-life processes is most likely to be accompanied by a decrease in entropy?

Accepted Answer

Condensation of steam on a bathroom mirror.

Question 16

A chemical plant wants to maximize the spontaneity of a reaction with $$\Delta H \u003c 0$$ and $$\Delta S \u003c 0. $$What strategy should they use?

Accepted Answer

Decrease the temperature.

Question 17

Which of the following statements about entropy is correct?

Accepted Answer

Entropy is a measure of the number of possible microstates of a system.

Question 18

Consider the reaction: $$\mathrm{2SO_2(g) + O_2$(g) \rightarrow 2SO_3(g)}. $$Predict the sign of $$\Delta S_{sys}$$ and justify your answer.

Accepted Answer

$$\Delta S_{sys} \u003c 0$$ because the number of gas molecules decreases.

Question 19

Which of the following best describes the effect of increasing temperature on the spontaneity of a reaction with $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0$$?

Accepted Answer

The reaction becomes more spontaneous.

Thermodynamics and Entropy Worksheet – Guided Study

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