Q: Which of the following best describes a mole in chemistry?

A mole is $$6.022 \times 10$$^{23}$$ atoms or molecules of a substance.

Question 1

Which law states that atoms are neither created nor destroyed during a chemical reaction, and how is this law applied when balancing chemical equations?

Accepted Answer

Law of Conservation of Matter; by balancing the number of each type of atom on both sides of the equation using coefficients.

Question 2

A reaction is given: $$2 \mathrm{H}_2 (g) + \mathrm{O}_2 (g) \rightarrow 2 \mathrm{H}_2\mathrm{O} (l). If $$you start with 10 mol of $$\mathrm{H}_2$$, how many moles of $$\mathrm{O}_2$$ are required for complete reaction?

Accepted Answer

$$5$$ mol

Question 3

Which of the following best describes a mole in chemistry?

Accepted Answer

A mole is $$6.022 	imes 10$$^{23}$$ atoms or molecules of a substance.

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: $$\mathrm{CH}_4 (g) + 2 \mathrm{O}_2 (g) \rightarrow \mathrm{CO}_2 (g) + 2 \mathrm{H}_2\mathrm{O} (l)$$, what is the oxidation state of carbon in methane and in carbon dioxide, respectively?

Accepted Answer

$$-4 in $$methane, $$+4 in $$carbon dioxide

Question 6

Which statement correctly describes what happens in a redox reaction?

Accepted Answer

One reactant is oxidized (loses electrons) and another is reduced (gains electrons).

Question 7

In the reaction $$\mathrm{C}_3\mathrm{H}_6\mathrm{O}_3 (aq) + \mathrm{NAD}^+ (aq) \rightarrow \mathrm{C}_3\mathrm{H}_4\mathrm{O}_3 (aq) + \mathrm{NADH} (aq) + \mathrm{H}^+ (aq)$$, which molecule is oxidized and which is the oxidant?

Accepted Answer

Lactic acid is oxidized; NAD$$^+ is $$the oxidant.

Question 8

Which of the following best describes an exothermic reaction?

Accepted Answer

It releases heat to the surroundings and has a negative $$\Delta H.$$

Question 9

A student dissolves NaCl in water and observes that the temperature of the solution decreases. Which terms best describe this process?

Accepted Answer

Endothermic, positive $$\Delta H$$

Question 10

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

Accepted Answer

Reaction of solid sodium with water to produce hydrogen gas.

Question 11

Which equation correctly relates free energy change ($$\Delta G$$), enthalpy change ($$\Delta H$$), temperature ($$T$$), and entropy change ($$\Delta S$$)?

Accepted Answer

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

Question 12

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst speeds up the reaction by lowering the activation energy.

Question 13

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 14

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

Accepted Answer

Adding a catalyst.

Question 15

A reaction has a negative $$\Delta G. $$Which of the following is TRUE?

Accepted Answer

The reaction is spontaneous and releases free energy.

Question 16

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

Accepted Answer

The reaction becomes more spontaneous as temperature increases.

Question 17

Which of the following statements about equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 18

For the reaction $$\mathrm{A} + \mathrm{B} \rightleftharpoons \mathrm{C} + \mathrm{D}$$, the equilibrium constant $$K_{eq} is $$given by:

Accepted Answer

$$K_{eq} = \frac{[C][D]}{[A][B]}$$

Question 19

Which of the following will increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst.

Chemical Reactions, Stoichiometry, Redox, Enthalpy, Thermodynamics, Kinetics, and Equilibrium: GOB Chemistry Study Guide

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