Q: Which process is most likely to be entropically favored?

Sublimation of dry ice ($$\text{CO}_2(s) \rightarrow \text{CO}_2(g)).$$

Q: Arrange the following ionic oxides in order of decreasing internal potential energy (from least stable to most stable): $$\text{Na}_2\text{O}$$, $$\text{CaO}$$, $$\text{K}_2\text{O}$$, $$\text{Al}_2\text{O}_3$$, $$\text{MgO}.$$

$$\text{Na}_2\text{O} \u003e \text{CaO} \u003e \text{K}_2\text{O} \u003e \text{Al}_2\text{O}_3 \u003e \text{MgO}$$

Q: Which of the following reactions is most likely to be reactant-favored at standard conditions?

$$6 \text{CO}_2(g) + 6 \text{H}_2\text{O}(g) \rightarrow \text{C}_6\text{H}_{12}\text{O}_6(s) + 6 \text{O}_2(g)$$

Question 1

Which of the following best explains why the reaction $$2 	ext{Mg}(s) + 	ext{O}_2(g) ightarrow 2 	ext{MgO}(s) is $$strongly product-favored under standard conditions?

Accepted Answer

The products have lower potential energy due to strong ionic bonds and fewer configurations than the reactants.

Question 2

Which factor is most important in determining the energetic stability of an ionic compound such as $$	ext{MgO}$$?

Accepted Answer

The strength of the electrostatic attraction between ions, as described by $$F = k \frac{q_1$ q_2$}{r^2$}.$$

Question 3

Consider the reaction $$	ext{C}_3	ext{H}_8(g) + 5 	ext{O}_2(g) ightarrow 3 	ext{CO}_2(g) + 4 	ext{H}_2	ext{O}(g). $$Which statement best explains why this reaction is product-favored?

Accepted Answer

The products have stronger bonds and more configurations than the reactants.

Question 4

Which of the following substances has the lowest potential energy and is therefore the most energetically stable?

Accepted Answer

$$	ext{MgO}(s)$$

Question 5

Which process is most likely to be entropically favored?

Accepted Answer

Sublimation of dry ice ($$	ext{CO}_2(s) ightarrow 	ext{CO}_2(g)).$$

Question 6

Given the following bond energies: $$	ext{C-C} = 347 kJ/$$mol, $$	ext{C=C} = 611 kJ/$$mol, $$	ext{C-O} = 360 kJ/$$mol, $$	ext{O-H} = 464 kJ/$$mol, $$	ext{C-H} = 414 kJ/$$mol. Calculate $$\Delta H_{rxn}$$ for a reaction where a $$	ext{C=C}$$ and an $$	ext{O-H}$$ bond are broken and a $$	ext{C-C}$$, $$	ext{C-O}$$, and $$	ext{C-H}$$ bond are formed.

Accepted Answer

$$\Delta H_{rxn} = -46 kJ/$$mol

Question 7

Which of the following changes will increase the entropy ($$S) of a $$system the most?

Accepted Answer

Evaporating a liquid to a gas.

Question 8

Arrange the following ionic oxides in order of decreasing internal potential energy (from least stable to most stable): $$	ext{Na}_2	ext{O}$$, $$	ext{CaO}$$, $$	ext{K}_2	ext{O}$$, $$	ext{Al}_2	ext{O}_3$$, $$	ext{MgO}.$$

Accepted Answer

$$	ext{Na}_2	ext{O} \u003e 	ext{CaO} \u003e 	ext{K}_2	ext{O} \u003e 	ext{Al}_2	ext{O}_3 \u003e 	ext{MgO}$$

Question 9

Which of the following best describes why $$	ext{H}_2	ext{O}(g)$$ has a higher standard molar entropy than $$	ext{H}_2	ext{O}(l)$$?

Accepted Answer

The gas phase allows for more configurations and greater freedom of movement.

Question 10

Which of the following reactions is most likely to be reactant-favored at standard conditions?

Accepted Answer

$$6 	ext{CO}_2(g) + 6 	ext{H}_2	ext{O}(g) ightarrow 	ext{C}_6	ext{H}_{12}	ext{O}_6(s) + 6 	ext{O}_2(g)$$

Question 11

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy increases as the number of possible configurations increases.

Question 12

Which of the following factors does NOT increase the entropy of a substance?

Accepted Answer

Decreasing the temperature.

Question 13

A reaction is exothermic ($$\Delta H_{rxn} \u003c 0) $$but results in a decrease in entropy ($$\Delta S_{rxn} \u003c 0). $$Which of the following best describes the directionality of this reaction?

Accepted Answer

The reaction may be product-favored at low temperatures, where enthalpy dominates.

Question 14

Which of the following best explains why $$	ext{Cl}_2(g)$$ has a higher standard molar entropy than $$	ext{O}_2(g)$$?

Accepted Answer

$$	ext{Cl}_2$$ has a higher molecular mass, allowing for more energy configurations.

Question 15

Which of the following is the best qualitative description of a process that is both energetically and entropically favored?

Accepted Answer

A process that releases energy and increases the number of configurations.

Question 16

Which of the following is the strongest intermolecular force present in liquid water?

Accepted Answer

Hydrogen bonding

Question 17

Which of the following best explains why ionic compounds with higher charges and smaller ionic radii are more energetically stable?

Accepted Answer

They have stronger electrostatic attractions, leading to lower potential energy.

Question 18

Which of the following processes would result in the largest increase in entropy?

Accepted Answer

Sublimation of $$	ext{CO}_2(s) to$$ $$	ext{CO}_2(g).$$

Predicting Chemical Change: Energetic and Entropic Factors in Reaction Directionality

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