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

$$\mathrm{\frac{actual\ yield}{theoretical\ yield} \times 100\%}$$

Question 1

Which of the following best describes the greenhouse effect as it relates to Earth's atmosphere?

Accepted Answer

Greenhouse gases allow sunlight to enter the atmosphere, warm Earth's surface, and trap some of the heat radiated from Earth's surface.

Question 2

Which of the following chemical equations is balanced and correctly represents the combustion of methane?

Accepted Answer

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

Question 3

A car engine burns octane ($$\mathrm{C_8H_{18}}) $$according to the equation: $$2\mathrm{C_8H_{18}(l)} + 25\mathrm{O_2$(g)} \rightarrow 16\mathrm{CO_2$(g)} + 18\mathrm{H_2O(g)}. If 22.0 $$moles of octane are burned, how many moles of $$\mathrm{CO_2$}$$ are produced?

Accepted Answer

176 moles

Question 4

Which quantity must always be the same on both sides of a balanced chemical equation?

Accepted Answer

The number of atoms of each kind

Question 5

If you have 4 pizza crusts, 10 cups of cheese, and 15 ounces of tomato sauce, and the recipe requires 1 crust, 2 cups cheese, and 5 ounces tomato sauce per pizza, what is the limiting reactant?

Accepted Answer

Tomato sauce

Question 6

A dose of milk of magnesia contains 3.26 g of $$\mathrm{Mg(OH)_2}. $$What mass of HCl (in g) is neutralized by this dose? (Balanced equation: $$\mathrm{Mg(OH)_2 + 2HCl \rightarrow $$MgCl_2$$ + 2H_2O}$$; molar masses: $$\mathrm{Mg(OH)_2} = 58.32 g/$$mol, HCl = 36.46 g/mol)

Accepted Answer

4.08 g

Question 7

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

Accepted Answer

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

Question 8

In the reaction $$2\mathrm{NO_2$(g)} + \mathrm{H_2O(l)} \rightarrow 2\mathrm{$$HNO_3$$(l)} + \mathrm{NO(g)}$$, if 5 mol $$\mathrm{NO_2$}$$ and 1 mol $$\mathrm{H_2O}$$ react completely, how many moles of $$\mathrm{NO_2$}$$ are left over?

Accepted Answer

2 mol

Question 9

A reaction of 167 g $$\mathrm{Fe_2O_3}$$ and 85.0 g CO produces 72.3 g Fe. If the theoretical yield is 113 g, what is the percent yield?

Accepted Answer

64%

Question 10

Which of the following is a correct balanced equation for the combustion of ethanol ($$\mathrm{C_2H_5OH}$$)?

Accepted Answer

$$\mathrm{C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(g)}$$

Question 11

Upon combustion of 0.8009 g of a compound containing only C, H, and O, 1.6004 g of $$\mathrm{CO_2$}$$ and 0.6551 g of $$\mathrm{H_2O}$$ are produced. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C_2H_4O}$$

Question 12

Which of the following reactions represents the reaction of an alkali metal with water?

Accepted Answer

$$\mathrm{2M(s) + 2H_2O(l) \rightarrow 2M^+(aq) + 2OH^-(aq) + H_2$(g)}$$

Question 13

If you burn $$4.0 	imes 10$$^{15}$$ g of octane ($$\mathrm{C_8H_{18}}$$), how many grams of $$\mathrm{$$CO_2$$}$$ are produced? (Molar masses: $$\mathrm{C_8H_{18}}$$ = 114.22 g/mol, $$\mathrm{$$CO_2$$}$$ = 44.01 g/mol, 2$$\mathrm{C_8H_{18}} + 25\mathrm{$$O_2$$} ightarrow 16\mathrm{$$CO_2$$} + 18\mathrm{H_2O}$$)

Accepted Answer

$$1.2 	imes 10$$^{16}$$ g

Question 14

Which of the following best describes the percent yield in a chemical reaction?

Accepted Answer

The ratio of the actual yield to the theoretical yield, multiplied by 100%

Question 15

Which of the following is a real-world example of a combustion reaction?

Accepted Answer

The burning of natural gas ($$\mathrm{CH_4$}) in a $$stove to produce heat, $$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}$$

Question 16

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 17

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

Accepted Answer

$$\mathrm{\frac{actual\ yield}{theoretical\ yield} 	imes 100\%}$$

Question 18

Which of the following best explains why the combustion of fossil fuels is linked to global warming?

Accepted Answer

Combustion of fossil fuels releases $$\mathrm{CO_2$}$$, a greenhouse gas, which traps heat in the atmosphere and increases Earth's average temperature.

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