Q: Which reaction is most likely to have a positive $$\Delta S of $$system?

$$\text{SiO}_2 (s) + 3 \text{C} (s) \rightarrow \text{SiC} (s) + 2 \text{CO} (g)$$

Question 1

Which of the following best describes the type of energy associated with the position of atoms or objects, such as a book sitting on a shelf?

Accepted Answer

Potential energy

Question 2

A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories of electricity does it use in three years? (1 kWh = $$3.60 	imes 10^6$ J, 1 kcal = 4184 J)

Accepted Answer

2.01 	imes $$10^5$ kcal

Question 3

According to the first law of thermodynamics, which of the following is true?

Accepted Answer

Energy can be transferred between a system and its surroundings.

Question 4

A system loses heat while doing work on the surroundings. What are the signs of $$q$$ and $$w$$?

Accepted Answer

$$q = -$$, $$w = -$$

Question 5

Which of the following processes is endothermic?

Accepted Answer

Water boiling

Question 6

Which of the following best represents an exothermic reaction?

Accepted Answer

CO$$_2$$ burning

Question 7

Energy is ________ to break a bond (endothermic process) and has a ______ sign.

Accepted Answer

absorbed, positive

Question 8

For the reaction: $$2 	ext{Mg} (s) + 	ext{O}_2 (g) ightarrow 2 	ext{MgO} (s)$$, $$\Delta H_{rxn} = -1204 kJ. $$How many grams of MgO are produced during an enthalpy change of $$-375 kJ$$?

Accepted Answer

31.3 g

Question 9

Which of the following processes results in a decrease in entropy ($$\Delta S) of $$the system?

Accepted Answer

Freezing water to form ice

Question 10

Which reaction is most likely to have a positive $$\Delta S of $$system?

Accepted Answer

$$	ext{SiO}_2 (s) + 3 	ext{C} (s) ightarrow 	ext{SiC} (s) + 2 	ext{CO} (g)$$

Question 11

What are the signs of $$\Delta H$$, $$\Delta S$$, and $$\Delta G$$ for the spontaneous conversion of a solid into a gas?

Accepted Answer

$$\Delta H \u003e 0$$, $$\Delta S \u003e 0$$, $$\Delta G \u003c 0$$

Question 12

A reaction has $$\Delta H = 125 kJ $$and $$\Delta S = 325 J/K. At $$what temperature in Celsius does the reaction become spontaneous?

Accepted Answer

385 °C

Question 13

Which of the following statements about chemical equilibrium is NOT correct?

Accepted Answer

The concentration of the reactants is equal to the concentration of the products.

Question 14

For the reaction $$2 	ext{NO} (g) + 	ext{O}_2 (g) ightarrow 2 	ext{NO}_2 (g)$$, the rate law is $$	ext{Rate} = k[	ext{NO}]^2[	ext{O}_2]. $$What happens to the rate if the concentration of NO is tripled?

Accepted Answer

The rate increases by a factor of 9.

Question 15

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It decreases the activation energy.

Question 16

Which of the following reactions will occur in the shortest amount of time?

Accepted Answer

Reaction B ($$E_a = 80 kJ)$$

Question 17

For the reaction $$	ext{CH}_4 (g) + 4 	ext{F}_2 (g) ightarrow 	ext{CF}_4 (g) + 4 	ext{HF} (g)$$, $$\Delta H = 38.2 kJ/$$mol, which change would yield more products?

Accepted Answer

Increase the temperature

Question 18

Which of the following best describes the entropy change ($$\Delta S) $$when a solid dissolves in water to form an aqueous solution?

Accepted Answer

$$\Delta S$$ increases

Question 19

Which of the following statements about the equilibrium constant $$K is $$correct?

Accepted Answer

If $$K \u003e 1$$, products are favored over reactants.

Study Guide: Chemical Reactions – Energy, Rate, and Equilibrium

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