Q: Which of the following is the correct definition of a mole (mol)?

The number of atoms or molecules equal to $$6.022 \times 10$$^{23}$$.

Question 1

Which of the following best describes the law of conservation of matter as it applies to chemical reactions?

Accepted Answer

The total number of atoms of each element is the same before and after a reaction.

Question 2

Given the reaction: $$2 \mathrm{H}_2 (g) + \mathrm{O}_2 (g) \rightarrow 2 \mathrm{H}_2\mathrm{O} (l)$$, how many moles of $$\mathrm{O}_2$$ are required to completely react with 10 moles of $$\mathrm{H}_2$$?

Accepted Answer

5 moles

Question 3

Which of the following is the correct definition of a mole (mol)?

Accepted Answer

The number of atoms or molecules equal to $$6.022 	imes 10$$^{23}$$.

Question 4

Which of the following is NOT a correct way to balance a chemical equation?

Accepted Answer

Changing the subscripts in chemical formulas.

Question 5

In the combustion of methane: $$\mathrm{CH}_4 (g) + 2 \mathrm{O}_2 (g) \rightarrow \mathrm{CO}_2 (g) + 2 \mathrm{H}_2\mathrm{O} (l)$$, which element is oxidized and which is reduced?

Accepted Answer

Carbon is oxidized, oxygen is reduced.

Question 6

Which of the following statements about oxidation numbers is correct?

Accepted Answer

The oxidation number of oxygen in most compounds is -2.

Question 7

A reaction has $$\Delta H = -250 \ \mathrm{kcal/mol}. $$Which of the following best describes this reaction?

Accepted Answer

Exothermic, energy is released.

Question 8

When NaCl dissolves in water and the solution temperature decreases, which terms best describe the process?

Accepted Answer

Endothermic, positive $$\Delta H$$

Question 9

Which of the following processes represents an increase in entropy ($$\Delta S$$)?

Accepted Answer

A solid dissolves in water to form an aqueous solution.

Question 10

Which equation correctly relates free energy, enthalpy, and entropy?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 11

A reaction is spontaneous if:

Accepted Answer

$$\Delta G is $$negative

Question 12

Which of the following will NOT increase the rate of a chemical reaction?

Accepted Answer

Decreasing the concentration of reactants

Question 13

Which of the following statements about catalysts is true?

Accepted Answer

A catalyst speeds up both the forward and reverse reactions.

Question 14

At equilibrium, which of the following is true for a chemical reaction?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 15

For the reaction $$2 \mathrm{Na} (s) + 2 \mathrm{H}_2\mathrm{O} (l) ightleftharpoons \mathrm{H}_2 (g) + 2 \mathrm{NaOH} (aq) + 	ext{heat}$$, what happens to the position of equilibrium if you add heat?

Accepted Answer

Shifts left

Question 16

Which of the following changes will NOT affect the equilibrium constant ($$K_{eq}) $$for a reaction?

Accepted Answer

Adding a catalyst

Question 17

Which of the following best describes an exergonic reaction?

Accepted Answer

It releases free energy and has a negative $$\Delta G.$$

Question 18

Which of the following statements about metabolic pathways is correct?

Accepted Answer

Catabolic pathways release a net amount of free energy.

Question 19

Which of the following is a correct statement about Le Châtelier’s Principle?

Accepted Answer

Removing product shifts the equilibrium to the right.

Question 20

Which of the following best describes the effect of increasing temperature on an endothermic reaction at equilibrium?

Accepted Answer

The equilibrium shifts to the right.

Lecture 3: Reactions of Molecules

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