Q: If 1.2 moles of $$\mathrm{S_8$}$$ and 1.0 moles of $$\mathrm{N_2$}$$ react according to $$\mathrm{S_8$ + 8\ N_2$ \rightarrow 8\ S_2N_2}$$, how many moles of $$\mathrm{S_2N_2}$$ can be formed?

$$1.0$$ moles$$\times\frac{8}{8}=1.0$$ moles, but $$\mathrm{N_2$} is $$limiting, so $$1.0$$ moles$$\div8=0.125$$ moles; $$\mathrm{S_8$} is in $$excess, so $$0.125\times8=1.0$$ moles. But the correct answer is $$0.40$$ moles.

Question 1

Which of the following best describes a chemical reaction?

Accepted Answer

A process in which atoms are rearranged to produce new molecules, resulting in the formation of new substances.

Question 2

Which of the following is the correct balanced chemical equation for the combustion of methane?

Accepted Answer

$$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(g)}$$

Question 3

In the balanced equation $$\mathrm{2\ Al(s) + 3\ O_2$(g) \rightarrow 2\ Al_2O_3(s)}$$, what does the symbol $$(s)$$ indicate?

Accepted Answer

The substance is in the solid state.

Question 4

Which of the following statements about stoichiometry is correct?

Accepted Answer

Stoichiometry relates the amounts of all substances in a chemical reaction using balanced equations.

Question 5

Given the balanced equation $$\mathrm{C_6H_{12}O_6$ + 6\ O_2$ \rightarrow 6\ CO_2$ + 6\ H_2O}$$, how many moles of water are produced from the complete combustion of 0.10 moles of glucose?

Accepted Answer

$$0.60$$ moles

Question 6

In a chemical reaction, what is the limiting reactant?

Accepted Answer

The reactant that is completely consumed first, thus limiting the amount of product formed.

Question 7

If 1.2 moles of $$\mathrm{S_8$}$$ and 1.0 moles of $$\mathrm{N_2$}$$ react according to $$\mathrm{S_8$ + 8\ N_2$ \rightarrow 8\ S_2N_2}$$, how many moles of $$\mathrm{S_2N_2}$$ can be formed?

Accepted Answer

$$1.0$$ moles$$	imes\frac{8}{8}=1.0$$ moles, but $$\mathrm{N_2$} is $$limiting, so $$1.0$$ moles$$\div8=0.125$$ moles; $$\mathrm{S_8$} is in $$excess, so $$0.125	imes8=1.0$$ moles. But the correct answer is $$0.40$$ moles.

Question 8

Which of the following best explains why chemical equations must be balanced?

Accepted Answer

To obey the Law of Conservation of Mass, which states that matter cannot be created or destroyed.

Question 9

In the reaction $$\mathrm{2\ Al(s) + 6\ HCl(aq) \rightarrow 2\ $$AlCl_3$$(aq) + 3\ H_2$(g)}$$, how many grams of $$\mathrm{H_2$}$$ can be produced from 5.0 g of $$\mathrm{Al}$$? (Molar mass of $$\mathrm{Al} = 27.0 g/$$mol, $$\mathrm{H_2$} = 2.0 g/$$mol)

Accepted Answer

$$1.1 g$$

Question 10

Which of the following is a correct interpretation of the coefficients in the balanced equation $$\mathrm{2\ C_4H_{10} + 13\ O_2$ \rightarrow 8\ CO_2$ + 10\ H_2O}$$?

Accepted Answer

2 moles of butane react with 13 moles of oxygen to produce 8 moles of carbon dioxide and 10 moles of water.

Question 11

A student mixes 10.0 g of $$\mathrm{P_2O_5}$$ with excess water. How many grams of $$\mathrm{H_3PO_4}$$ can be produced? (Molar mass: $$\mathrm{P_2O_5} = 142 g/$$mol, $$\mathrm{H_3PO_4} = 98 g/$$mol; $$\mathrm{P_2O_5} + 3\ H_2O \rightarrow 2\ H_3PO_4)$$

Accepted Answer

$$6.9 g$$

Question 12

Which of the following is NOT a correct symbol used in chemical equations?

Accepted Answer

$$(m)$$ for mixture

Question 13

In a real-world scenario, why is the actual yield of a chemical reaction often less than the theoretical yield?

Accepted Answer

Because side reactions, incomplete reactions, and loss of product during recovery can occur.

Question 14

If 5 molecules of $$\mathrm{CH_4$}$$ and 8 molecules of $$\mathrm{O_2$}$$ react according to $$\mathrm{CH_4$ + 2\ O_2$ \rightarrow CO_2$ + 2\ H_2O}$$, which is the limiting reactant?

Accepted Answer

$$\mathrm{O_2$}$$

Question 15

Which of the following best describes the term 'excess reactant'?

Accepted Answer

A reactant that is not completely consumed in a chemical reaction.

Question 16

A pizza recipe requires 1 crust, 5 oz. tomato sauce, and 2 oz. cheese to make 1 pizza. If you have 4 crusts, 15 oz. tomato sauce, and 10 oz. cheese, what is the limiting ingredient?

Accepted Answer

All ingredients are present in the exact ratio, so none is limiting.

Question 17

Which of the following is a correct statement about 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 18

In the reaction $$\mathrm{2\ C_4H_{10} + 13\ O_2$ \rightarrow 8\ CO_2$ + 10\ H_2O}$$, how many moles of $$\mathrm{CO_2$}$$ are produced from 22 moles of $$\mathrm{C_4H_{10}}$$?

Accepted Answer

$$88$$ moles

Question 19

Which of the following is the best definition of a balanced chemical equation?

Accepted Answer

An equation in which the number of atoms of each element is the same on both sides of the equation.

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