Q: A reaction has a theoretical yield of 50.0 g but only 40.0 g of product is actually obtained. What is the percent yield?

$$ \frac{40.0}{50.0} \times 100\% = 80\% $$

Q: If the actual yield of MgCl$$_2 is 28.5 g $$and the theoretical yield is 50.60 g, what is the percent yield?

$$ \frac{28.5}{50.60} \times 100\% = 56.4\% $$

Question 1

Which of the following best describes the greenhouse effect as illustrated in the provided diagram?

Accepted Answer

Greenhouse gases trap some of the heat radiated from Earth's surface, warming the planet.

Question 2

Based on the atmospheric carbon dioxide graph, what trend is observed from 1860 to 2020?

Accepted Answer

Atmospheric CO$$_2$$ concentration has increased significantly.

Question 3

Which equation correctly represents the complete combustion of methane, as shown in the diagrams?

Accepted Answer

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

Question 4

Which of the following is the correct set of physical state symbols used in chemical equations?

Accepted Answer

(s) for solid, (l) for liquid, (g) for gas, (aq) for dissolved in water

Question 5

A reaction is represented as: $$ \mathrm{2H_2(g) + O_2(g) \rightarrow 2H_2O(l)} . If $$you start with 4.0 g of H$$_2$$ and 32.0 g of O$$_2$$, what is the mass of water produced?

Accepted Answer

36.0 g

Question 6

Which of the following best explains why the coefficients in a balanced chemical equation are important for stoichiometric calculations?

Accepted Answer

They indicate the ratio of moles of reactants and products.

Question 7

In the pizza analogy for limiting reactants, if you have 4 crusts, 10 cups of cheese, and 15 oz of tomato sauce, how many pizzas can you make?

Accepted Answer

3

Question 8

Given the reaction: $$ \mathrm{2H_2 + O_2 \rightarrow 2H_2O} $$, which mixture produces the greatest amount of water?

Accepted Answer

2 mol H$$_2$$ and 1 mol O$$_2$$

Question 9

If 68.5 kg of CO reacts with 8.60 kg of H$$_2 to $$produce methanol ($$ \mathrm{CH_3OH} $$), what is the theoretical yield of methanol in grams? (Molar masses: CO = 28.01 g/mol, H$$_2 = 2.02 g/$$mol, CH$$_3OH = 32.04 g/$$mol)

Accepted Answer

137,000 g

Question 10

A reaction has a theoretical yield of 50.0 g but only 40.0 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$ \frac{40.0}{50.0} 	imes 100\% = 80\% $$

Question 11

Which of the following is the limiting reactant when 2.50 g of N$$_2$$ reacts with 2.00 g of H$$_2 to $$form NH$$_3$$? (Molar masses: N$$_2 = 28.02 g/$$mol, H$$_2 = 2.02 g/$$mol)

Accepted Answer

H$$_2$$

Question 12

In the reaction $$ \mathrm{Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)} $$, if you start with 45.10 g Fe$$_2O$_3$$ and 29.56 g CO, which reactant is in excess?

Accepted Answer

CO

Question 13

Which of the following best explains why the actual yield of a chemical reaction is often less than the theoretical yield?

Accepted Answer

Because some product is lost due to side reactions or incomplete reactions.

Question 14

If methane ($$ \mathrm{CH_4} ) $$reacts with oxygen to produce 15.0 g of water, what mass of methane is required? (Molar masses: CH$$_4 = 16.04 g/$$mol, H$$_2O = 18.02 g/$$mol)

Accepted Answer

6.68 g

Question 15

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You can only change the coefficients to balance the equation.

Question 16

Given the reaction: $$ \mathrm{A + 5B \rightarrow 3C + 4D} $$, when equal masses of A and B are reacted, which is limiting if the molar mass of A is less than that of B?

Accepted Answer

B is limiting

Question 17

Which of the following is a greenhouse gas that contributes to global warming?

Accepted Answer

CO$$_2$$

Question 18

If the actual yield of MgCl$$_2 is 28.5 g $$and the theoretical yield is 50.60 g, what is the percent yield?

Accepted Answer

$$ \frac{28.5}{50.60} 	imes 100\% = 56.4\% $$

Question 19

Which of the following best describes the relationship between atmospheric CO$$_2$$ and global temperature based on the provided graphs?

Accepted Answer

As atmospheric CO$$_2$$ increases, global temperature tends to increase.

Chemical Reactions and Chemical Quantities: Stoichiometry, Limiting Reactants, and Yield

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