Q: What is the percent yield if the theoretical yield of $$\mathrm{N_2$} is 3.74 g $$and the actual yield is 2.80 g?

$$\displaystyle \frac{2.80}{3.74} \times 100\% = 74.9\%$$

Question 1

Which of the following best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total mass of the reactants equals the total mass of the products.

Question 2

What is the balanced chemical equation for the combustion of butane ($$\mathrm{C_4H_{10}}$$)?

Accepted Answer

$$\mathrm{2\ C_4H_{10}(l) + 13\ O_2$(g) \rightarrow 8\ CO_2$(g) + 10\ H_2O(g)}}$$

Question 3

Which symbol in a chemical equation indicates that a substance is dissolved in water?

Accepted Answer

(aq)

Question 4

Given the reaction $$\mathrm{2\ NH_3$(g) + 3\ CuO(s) \rightarrow N_2$(g) + 3\ Cu(s) + 3\ H_2O(l)}$$, how many grams of $$\mathrm{N_2$}$$ can be produced from 9.05 g of $$\mathrm{NH_3$}$$ and 45.2 g of $$\mathrm{CuO}$$? (Molar masses: $$\mathrm{NH_3$} = 17.03 g/$$mol, $$\mathrm{CuO} = 79.55 g/$$mol, $$\mathrm{N_2$} = 28.02 g/$$mol)

Accepted Answer

3.74 g

Question 5

In the reaction $$\mathrm{4\ Al(s) + 3\ O_2$(g) \rightarrow 2\ Al_2O_3(s)}$$, if you start with 10.0 g of Al and 10.0 g of $$\mathrm{O_2$}$$, which is the limiting reactant? (Molar masses: Al = 26.98 g/mol, $$\mathrm{O_2$} = 32.00 g/$$mol)

Accepted Answer

Oxygen

Question 6

What is the percent yield if the theoretical yield of $$\mathrm{N_2$} is 3.74 g $$and the actual yield is 2.80 g?

Accepted Answer

$$\displaystyle \frac{2.80}{3.74} 	imes 100\% = 74.9\%$$

Question 7

Which of the following statements about stoichiometry is correct?

Accepted Answer

Stoichiometry is the study of the numerical relationship between chemical quantities in a chemical reaction.

Question 8

For the reaction $$\mathrm{2\ C_8H_{18}(l) + 25\ O_2$(g) \rightarrow 16\ CO_2$(g) + 18\ H_2O(g)}$$, how many moles of $$\mathrm{CO_2$}$$ are produced from 5.00 moles of $$\mathrm{C_8H_{18}}$$?

Accepted Answer

40.0 moles

Question 9

A reaction mixture contains 42.5 g Mg and 33.8 g $$\mathrm{O_2$}. $$Using the reaction $$\mathrm{2\ Mg(s) + O_2$(g) \rightarrow 2\ MgO(s)}$$, what is the theoretical yield of $$\mathrm{MgO} in $$grams? (Molar masses: Mg = 24.31 g/mol, $$\mathrm{O_2$} = 32.00 g/$$mol, $$\mathrm{MgO} = 40.31 g/$$mol)

Accepted Answer

70.5 g

Question 10

Which of the following is the correct sequence for a mass-to-mass stoichiometric calculation?

Accepted Answer

Mass A $$\rightarrow$$ Amount A (in moles) $$\rightarrow$$ Amount B (in moles) $$\rightarrow$$ Mass B

Question 11

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

Accepted Answer

Because some product may be lost during collection or side reactions may occur.

Question 12

Which reactant is the limiting reactant if you have 5 molecules of $$\mathrm{CH_4$}$$ and 8 molecules of $$\mathrm{O_2$}$$ for the reaction $$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(g)}$$?

Accepted Answer

$$\mathrm{O_2$}$$

Question 13

Which of the following is NOT a correct guideline for balancing chemical equations?

Accepted Answer

Balance the number of oxygen atoms first.

Question 14

If 37.8 g of $$\mathrm{CO_2$} is $$used in photosynthesis ($$\mathrm{6\ CO_2$ + 6\ H_2O \rightarrow C_6H_{12}O_6$ + 6\ O_2$}$$), how many grams of glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass = 180.16 g/mol) can be synthesized? (Molar mass $$\mathrm{CO_2$} = 44.01 g/$$mol)

Accepted Answer

15.5 g

Question 15

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

Accepted Answer

The reactant that is completely consumed and limits the amount of product formed.

Question 16

A student mixes 10.0 g of $$\mathrm{C_4H_{10}}$$ with excess $$\mathrm{O_2$}$$ and ignites the mixture. What is the theoretical yield of $$\mathrm{CO_2$} in $$grams? (Balanced equation: $$\mathrm{2\ C_4H_{10}(l) + 13\ O_2$(g) \rightarrow 8\ CO_2$(g) + 10\ H_2O(g)}$$, molar masses: $$\mathrm{C_4H_{10}} = 58.12 g/$$mol, $$\mathrm{CO_2$} = 44.01 g/$$mol)

Accepted Answer

60.6 g

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