Question 1

Which of the following best describes the main purpose of balancing a chemical equation?

Accepted Answer

To ensure that the number of atoms of each element is conserved during the reaction.

Question 2

A student mixes aqueous solutions of $$\mathrm{$$CuCl_2$$}$$ and $$\mathrm{Na_2CO_3}. $$What is the expected observation and why?

Accepted Answer

A blue precipitate forms because $$\mathrm{$$CuCO_3$$} is $$insoluble.

Question 3

Which of the following is the correct balanced equation for the complete combustion of propane ($$\mathrm{C_3H_8}$$)?

Accepted Answer

$$\mathrm{C_3H_8(g) + 5 O_2$(g) \rightarrow 3 CO_2$(g) + 4 H_2O(l)}$$

Question 4

If 50 molecules of ethanol ($$\mathrm{C_2H_6O}) $$are completely combusted, how many molecules of $$\mathrm{CO_2$}$$ are produced according to the equation $$\mathrm{C_2H_6O(l) + 3 O_2$(g) \rightarrow 2 CO_2$(g) + 3 H_2O(l)}$$?

Accepted Answer

100

Question 5

Which of the following factors will NOT increase the rate of a gas-phase chemical reaction?

Accepted Answer

Decreasing the pressure.

Question 6

Which statement best explains why a catalyst increases the rate of a chemical reaction?

Accepted Answer

It lowers the activation energy ($$E_a) $$required for the reaction.

Question 7

Consider the reaction: $$2 \mathrm{H_2S(g)} + 3 \mathrm{O_2$(g)} \rightarrow 2 \mathrm{H_2O(g)} + 2 \mathrm{SO_2$(g)}. If $$you start with 4 molecules of $$\mathrm{H_2S}$$ and 6 molecules of $$\mathrm{O_2$}$$, which is the limiting reactant?

Accepted Answer

Neither, both are in exact stoichiometric proportion.

Question 8

Which of the following reactions is most likely to be product-favored at all temperatures?

Accepted Answer

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

Question 9

Which of the following best describes the energy change in an exothermic reaction?

Accepted Answer

The products have lower potential energy than the reactants.

Question 10

For the reaction $$2 \mathrm{NO_2$(g)} \rightleftharpoons \mathrm{N_2O_4(g)}$$, which of the following is true about the reaction extent at low temperature?

Accepted Answer

It is product-favored at low temperature.

Question 11

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

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

Question 12

Which of the following changes will increase the rate of a reaction between two gases in a closed container?

Accepted Answer

Increasing the pressure.

Question 13

Which of the following is a signature feature of all chemical reactions?

Accepted Answer

They involve the rearrangement of atoms to form new substances.

Question 14

In the photosynthesis reaction $$6 \mathrm{CO_2$(g)} + 6 \mathrm{H_2O(l)} \rightarrow \mathrm{C_6H_{12}O_6$(s)} + 6 \mathrm{O_2$(g)}$$, what is the role of sunlight?

Accepted Answer

It provides the activation energy for the endothermic reaction.

Question 15

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

It increases the number of effective collisions by increasing particle speed.

Question 16

Which of the following reactions is more likely to be faster due to higher configuration effectiveness?

Accepted Answer

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

Question 17

Which of the following is true about the effect of activation energy ($$E_a) on $$reaction rate?

Accepted Answer

A lower $$E_a$$ means more particles have enough energy to react.

Question 18

For the reaction $$3 \mathrm{O_2$(g)} \rightleftharpoons 2 \mathrm{O_3$(g)}$$ with $$\Delta H_{rxn} = 284\ \mathrm{kJ/mol}$$ and $$E_a = 498.5\ \mathrm{kJ/mol}$$, what can be said about the reaction extent?

Accepted Answer

It is reactant-favored at all temperatures.

Question 19

Which of the following best describes a limiting reactant in a chemical reaction?

Accepted Answer

It is the reactant that determines the maximum amount of product formed.

Modeling and Characterizing Chemical Reactions: Stoichiometry, Thermochemistry, Kinetics, and Equilibrium

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