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

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

Question 1

A recipe for pancakes requires 2 eggs to make 5 pancakes. If you have 12 eggs and unlimited other ingredients, how many pancakes can you make?

Accepted Answer

30 pancakes

Question 2

Given the balanced equation $$3 \mathrm{H}_2(g) + \mathrm{N}_2(g) \rightarrow 2 \mathrm{NH}_3(g)$$, how many moles of $$\mathrm{NH}_3$$ can be produced from 6 moles of $$\mathrm{H}_2$$ and excess $$\mathrm{N}_2$$?

Accepted Answer

4 moles

Question 3

For the reaction $$2 \mathrm{C}_8\mathrm{H}_{18}(l) + 25 \mathrm{O}_2(g) ightarrow 16 \mathrm{CO}_2(g) + 18 \mathrm{H}_2\mathrm{O}(g)$$, how many grams of $$\mathrm{CO}_2$$ are produced from $$5.0 	imes 10^2$ g of pure octane ($$\mathrm{C}_8\mathrm{H}_{18}$$)? (Molar mass $$\mathrm{C}_8\mathrm{H}_{18} = 114.3$$ g/mol, $$\mathrm{CO}_2 = 44.01$$ g/mol)

Accepted Answer

$$1.5 	imes 10^3$ g

Question 4

In the reaction $$\mathrm{Cu}_2\mathrm{O}(s) + \mathrm{C}(s) \rightarrow 2 \mathrm{Cu}(s) + \mathrm{CO}(g)$$, if you start with 11.5 g $$\mathrm{Cu}_2\mathrm{O}$$ and 114.5 g $$\mathrm{C}$$, which is the limiting reactant?

Accepted Answer

$$\mathrm{Cu}_2\mathrm{O}$$

Question 5

For the same reaction above, if the actual yield of $$\mathrm{Cu} is 87.4 g $$and the theoretical yield is 101.7 g, what is the percent yield?

Accepted Answer

$$85.9\%$$

Question 6

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat and have a negative $$\Delta H_{rxn}.$$

Question 7

A propane tank contains $$1.18 	imes 10^4$ g of $$\mathrm{C}_3\mathrm{H}_8$$. Given $$\Delta H_{rxn} = -2044$$ kJ for $$\mathrm{C}_3\mathrm{H}_8(g) + 5 \mathrm{O}_2(g) ightarrow 3 \mathrm{CO}_2(g) + 4 \mathrm{H}_2\mathrm{O}(g)$$, how much heat (in kJ) is released when all the propane is combusted? (Molar mass $$\mathrm{C}_3\mathrm{H}_8 = 44.11$$ g/mol)

Accepted Answer

$$-5.47 	imes 10^5$ kJ

Question 8

For the reaction $$\mathrm{K} + \mathrm{S} \rightarrow \mathrm{K}_2\mathrm{S}$$, how many atoms of sulfur will react with 52 atoms of potassium?

Accepted Answer

26 atoms

Question 9

For the reaction $$2\mathrm{HCl} + \mathrm{Zn} \rightarrow \mathrm{H}_2 + \mathrm{ZnCl}_2$$, if you start with 2 moles of HCl and 1 mole of Zn, what is the limiting reactant?

Accepted Answer

Neither is limiting

Question 10

In a reaction, the actual yield is always:

Accepted Answer

Equal to or less than the theoretical yield

Question 11

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

Accepted Answer

The reactant that is completely consumed first

Question 12

If 8 car bodies and 48 tires are available to make cars (each car requires 4 tires), how many complete cars can be made and how many tires will be left over?

Accepted Answer

8 cars, 16 tires left over

Question 13

For the reaction $$\mathrm{Na} + \mathrm{S} \rightarrow \mathrm{Na}_2\mathrm{S}$$, how many moles of sulfur will react with 158 moles of sodium?

Accepted Answer

79 moles

Question 14

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

Accepted Answer

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

Question 15

Which of the following best describes an endothermic reaction?

Accepted Answer

A reaction that absorbs heat from the surroundings

Question 16

In the reaction $$\mathrm{Pb(NO}_3)_2 + \mathrm{K}_2\mathrm{SO}_4 \rightarrow 2\mathrm{KNO}_3 + \mathrm{PbSO}_4$$, if 22.9 g of $$\mathrm{Pb(NO}_3)_2 is $$reacted with excess $$\mathrm{K}_2\mathrm{SO}_4$$ and 2.41 g of $$\mathrm{KNO}_3$$ are recovered, what is the percent yield of $$\mathrm{KNO}_3$$? (Molar mass $$\mathrm{Pb(NO}_3)_2 = 331.2 g/$$mol, $$\mathrm{KNO}_3 = 101.1 g/$$mol)

Accepted Answer

31.7\%

Stoichiometry, Limiting Reactants, and Enthalpy in Chemical Reactions

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