Q: Which of the following is the correct formula for percent yield?

$$ \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100\% $$

Question 1

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

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 images?

Accepted Answer

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

Question 4

What is the correct set of physical state symbols for the following substances: solid sodium chloride, liquid water, oxygen gas, and aqueous hydrochloric acid?

Accepted Answer

$$ \mathrm{NaCl(s), H_2O(l), O_2(g), HCl(aq)} $$

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 mass of H$$_2O is $$produced?

Accepted Answer

36.0 g

Question 6

In the reaction $$ \mathrm{3H_2(g) + N_2(g) \rightarrow 2NH_3(g)} $$, if you have 6 moles of H$$_2$$ and 2 moles of N$$_2$$, which is the limiting reactant?

Accepted Answer

Neither, both are in exact stoichiometric ratio

Question 7

Which of the following best explains why the coefficients in a balanced chemical equation must not be changed by altering subscripts?

Accepted Answer

Changing subscripts changes the identity of the substances involved.

Question 8

Given the reaction: $$ \mathrm{2C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)} $$, how many moles of CO$$_2$$ are produced from 1 mole of C$$_8H$_{18}$$?

Accepted Answer

8

Question 9

If 10 cups of cheese, 4 crusts, and 15 ounces of tomato sauce are available for making pizzas (1 crust + 5 oz sauce + 2 cups cheese = 1 pizza), what is the theoretical yield of pizzas?

Accepted Answer

3

Question 10

A reaction mixture contains 45.10 g Fe$$_2O$_3$$ and 29.56 g CO. The reaction is: $$ \mathrm{Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)} . $$After the reaction, what is the mass of the excess reactant remaining?

Accepted Answer

Fe$$_2O$_3 is in $$excess; calculate the remaining mass after CO is consumed.

Question 11

Which of the following is the correct formula for percent yield?

Accepted Answer

$$ \frac{	ext{Actual yield}}{	ext{Theoretical yield}} 	imes 100\% $$

Question 12

In the reaction $$ \mathrm{N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)} $$, how many grams of NH$$_3$$ can be formed from 2.50 g N$$_2$$ and 2.00 g H$$_2$$?

Accepted Answer

3.06 g

Question 13

Methanol is produced by the reaction: $$ \mathrm{CO(g) + 2H_2(g) \rightarrow CH_3OH(g)} . If 68.5 kg CO $$reacts with 8.60 kg H$$_2$$, what is the theoretical yield of CH$$_3OH$$?

Accepted Answer

8.60 kg H$$_2 is $$limiting; calculate moles of H$$_2$$ and convert to grams of CH$$_3OH.$$

Question 14

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is completely consumed first and determines the maximum amount of product.

Question 15

If the actual yield of MgCl$$_2 in a $$reaction 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 16

Which of the following best explains 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.

Question 17

In a reaction where 3.25 g of N$$_2$$ reacts with excess O$$_2 to $$form N$$_2O$_3$$, and 5.2 g of N$$_2O$_3$$ are actually produced, what is the percent yield?

Accepted Answer

Percent yield = $$ \frac{5.2}{theoretical\ yield} 	imes 100\% $$

Question 18

Which of the following is NOT a greenhouse gas?

Accepted Answer

N$$_2$$

Question 19

If 2 mol H$$_2$$ and 1 mol O$$_2$$ are reacted according to $$ \mathrm{2H_2 + O_2 \rightarrow 2H_2O} $$, what is the limiting reactant and how many moles of H$$_2O $$are produced?

Accepted Answer

H$$_2 is $$limiting; 2 mol H$$_2O $$produced.

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