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

$$\text{Theoretical yield} = \text{moles of limiting reactant} \times \frac{\text{moles of product}}{\text{moles of limiting reactant}} \times \text{molar mass of product}$$

Question 1

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

Accepted Answer

The reactant that determines the maximum amount of product that can be formed.

Question 2

In the reaction $$2\mathrm{C}_2\mathrm{H}_2 (g) + 5\mathrm{O}_2 (g) \rightarrow 4\mathrm{CO}_2 (g) + 2\mathrm{H}_2\mathrm{O} (g)$$, how many grams of $$\mathrm{CO}_2$$ are produced when $$54.6 g of$$ $$\mathrm{C}_2\mathrm{H}_2 is $$burned? (Molar masses: $$\mathrm{C}_2\mathrm{H}_2 = 26.04 g/$$mol, $$\mathrm{CO}_2 = 44.01 g/$$mol)

Accepted Answer

$$185 g$$

Question 3

A student mixes $$25.0 g of Fe $$and $$40.0 g of$$ $$\mathrm{H}_2\mathrm{O} in $$the reaction $$3\mathrm{Fe} + 4\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Fe}_3\mathrm{O}_4 + 4\mathrm{H}_2. If$$ $$31.1 g of$$ $$\mathrm{Fe}_3\mathrm{O}_4 is $$actually produced, what is the percent yield? (Molar mass $$\mathrm{Fe}_3\mathrm{O}_4 = 231.55 g/$$mol)

Accepted Answer

$$89.9\%$$

Question 4

Which of the following is the correct balanced equation for the reaction of aluminum with chlorine to form aluminum chloride?

Accepted Answer

$$2\mathrm{Al} + 3\mathrm{Cl}_2 \rightarrow 2\mathrm{AlCl}_3$$

Question 5

Propane ($$\mathrm{C}_3\mathrm{H}_8) $$combusts in oxygen according to the equation: $$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}. $$How many moles of $$\mathrm{CO}_2$$ are produced when $$2.25$$ mol of $$\mathrm{C}_3\mathrm{H}_8$$ reacts completely?

Accepted Answer

$$6.75$$ mol

Question 6

In the reaction $$2\mathrm{Fe} + 3\mathrm{S} \rightarrow \mathrm{Fe}_2\mathrm{S}_3$$, how many moles of sulfur are needed to react with $$1.42$$ mol of iron?

Accepted Answer

$$1.06$$ mol

Question 7

Heptane ($$\mathrm{C}_7\mathrm{H}_{16}) $$combusts according to $$\mathrm{C}_7\mathrm{H}_{16} + 11\mathrm{O}_2 \rightarrow 7\mathrm{CO}_2 + 8\mathrm{H}_2\mathrm{O}. $$How many grams of $$\mathrm{O}_2$$ are required to react with $$22.50 g of $$heptane? (Molar mass $$\mathrm{C}_7\mathrm{H}_{16} = 100.21 g/$$mol, $$\mathrm{O}_2 = 32.00 g/$$mol)

Accepted Answer

$$79.8 g$$

Question 8

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

Accepted Answer

The ratio of actual yield to theoretical yield, multiplied by 100.

Question 9

Given the unbalanced reaction $$\mathrm{N}_2 + \mathrm{O}_2 \rightarrow \mathrm{N}_2\mathrm{O}_4$$, if $$15.0 g of$$ $$\mathrm{N}_2\mathrm{O}_4 is $$produced, how many moles of $$\mathrm{O}_2$$ were required? (Molar mass $$\mathrm{N}_2\mathrm{O}_4 = 92.02 g/$$mol)

Accepted Answer

$$0.163$$ mol

Question 10

A reaction has a theoretical yield of $$79.2 g $$and an actual yield of $$62.0 g. $$What is the percent yield?

Accepted Answer

$$78.3\%$$

Question 11

If $$4.40$$ mol of Al reacts with chlorine gas according to $$2\mathrm{Al} + 3\mathrm{Cl}_2 \rightarrow 2\mathrm{AlCl}_3$$, how many moles of $$\mathrm{Cl}_2$$ are needed?

Accepted Answer

$$6.60$$ mol

Question 12

In a reaction, $$45.0 g of Al $$and $$62.0 g of$$ $$\mathrm{Cl}_2$$ are mixed to form $$\mathrm{AlCl}_3. If$$ $$66.5 g of$$ $$\mathrm{AlCl}_3 is $$actually obtained, what is the percent yield? (Molar masses: $$\mathrm{Al} = 26.98 g/$$mol, $$\mathrm{Cl}_2 = 70.90 g/$$mol, $$\mathrm{AlCl}_3 = 133.34 g/$$mol)

Accepted Answer

$$77.7\%$$

Question 13

Which of the following statements about the excess reactant is correct?

Accepted Answer

It is the reactant that remains after the reaction is complete.

Question 14

A welder uses acetylene ($$\mathrm{C}_2\mathrm{H}_2) $$and oxygen to produce high temperatures. If $$2.00$$ mol of $$\mathrm{C}_2\mathrm{H}_2$$ reacts, how many moles of $$\mathrm{CO}_2$$ are produced according to $$2\mathrm{C}_2\mathrm{H}_2 + 5\mathrm{O}_2 \rightarrow 4\mathrm{CO}_2 + 2\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

$$4.00$$ mol

Question 15

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

Accepted Answer

$$	ext{Theoretical yield} = 	ext{moles of limiting reactant} 	imes \frac{	ext{moles of product}}{	ext{moles of limiting reactant}} 	imes 	ext{molar mass of product}$$

Question 16

Nitrogen dioxide reacts with water to produce nitric acid and nitrogen oxide. Which of the following is the balanced equation for this reaction?

Accepted Answer

$$3\mathrm{NO}_2 + \mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{HNO}_3 + \mathrm{NO}$$

Question 17

If $$8.25 g of$$ $$\mathrm{NO}_2$$ reacts according to $$3\mathrm{NO}_2 + \mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{HNO}_3 + \mathrm{NO}$$, how many grams of $$\mathrm{HNO}_3$$ are produced? (Molar masses: $$\mathrm{NO}_2 = 46.01 g/$$mol, $$\mathrm{HNO}_3 = 63.01 g/$$mol)

Accepted Answer

$$7.53 g$$

Question 18

Which of the following best describes stoichiometry?

Accepted Answer

The calculation of quantities of reactants and products in chemical reactions.

Question 19

A chemist reacts $$4.0 	imes 10$$^{-3}$$ mol of $$\mathrm{O}_2$$ with excess $$\mathrm{N}_2$$ to form $$\mathrm{N}_2\mathrm{O}_4$$. How many grams of $$\mathrm{N}_2$$ are needed? (Molar mass $$\mathrm{N}_2 = 28.02$$ g/mol)

Accepted Answer

$$0.112 g$$

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