Question 1

Which statement best describes the law of conservation of mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

Given the unbalanced equation: $$\mathrm{CH_4$ + O_2$ \rightarrow CO_2$ + H_2O}$$, what are the correct coefficients to balance the equation?

Accepted Answer

$$1, 2, 1, 2$$

Question 3

A student burns 0.655 g of propane ($$\mathrm{C_3H_8}) in $$excess oxygen and collects 2.00 g of $$\mathrm{CO_2$}$$ and 1.08 g of $$\mathrm{H_2O}. $$Does this experiment support the law of conservation of mass?

Accepted Answer

No, because the total mass of products is greater than the mass of reactants.

Question 4

Which of the following best defines a stoichiometric coefficient in a balanced chemical equation?

Accepted Answer

The number placed in front of a chemical formula to indicate the relative number of moles of that substance.

Question 5

Which of the following is a combination (synthesis) reaction?

Accepted Answer

$$\mathrm{2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)}$$

Question 6

A chemical equation is unbalanced if:

Accepted Answer

The number of atoms of at least one element is not the same on both sides of the equation.

Question 7

Which of the following best represents a decomposition reaction?

Accepted Answer

$$\mathrm{2H_2O_2(l) \rightarrow 2H_2O(l) + O_2$(g)}$$

Question 8

In the reaction $$\mathrm{2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)}$$, how many moles of $$\mathrm{O_2$}$$ are required to completely react with 4 moles of $$\mathrm{H_2$}$$?

Accepted Answer

2 moles

Question 9

Which of the following is a correct statement about combustion reactions?

Accepted Answer

They are rapid reactions that produce a flame and usually involve $$\mathrm{O_2$} as a $$reactant.

Question 10

Balance the following equation for the combustion of ethanol: $$\mathrm{C_2H_5OH(l) + O_2$(g) \rightarrow CO_2$(g) + H_2O(l)}$$

Accepted Answer

$$1, 3, 2, 3$$

Question 11

A reaction is represented by the following diagram: 2 red spheres (A) combine with 1 blue sphere (B) to form a molecule. Which equation best represents this reaction?

Accepted Answer

$$\mathrm{2A + B \rightarrow A_2B}$$

Question 12

Which of the following best describes the role of coefficients in a balanced chemical equation?

Accepted Answer

They indicate the relative number of moles of each substance involved in the reaction.

Question 13

If 0.350 mol of $$\mathrm{$$CaCO_3$$} is $$decomposed according to $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$, how many moles of $$\mathrm{CO_2$}$$ are produced?

Accepted Answer

0.350 mol

Question 14

Which of the following is NOT a correct symbol for the physical state of a substance in a chemical equation?

Accepted Answer

$$(p)$$ for plasma

Question 15

A reaction vessel contains 2.0 mol of $$\mathrm{H_2$}$$ and 1.0 mol of $$\mathrm{O_2$}. $$According to $$\mathrm{2H_2 + O_2$ \rightarrow 2H_2O}$$, what is the limiting reactant?

Accepted Answer

Neither, they are present in stoichiometric proportions

Question 16

Which of the following best describes a chemical reaction?

Accepted Answer

A process in which atoms are rearranged to form new substances.

Question 17

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

Accepted Answer

$$\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}$$

Question 18

Which of the following is a decomposition reaction that could occur in a car airbag during a crash?

Accepted Answer

$$\mathrm{2NaN_3(s) \rightarrow 2Na(s) + 3N_2(g)}$$

Question 19

A student is asked to balance the following equation: $$\mathrm{C_2H_6 + O_2$ \rightarrow CO_2$ + H_2O}. $$What is the correct set of coefficients?

Accepted Answer

$$2, 7, 4, 6$$

Chemical Reactions, Stoichiometry, and Reaction Types: General Chemistry Study Notes

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