Q: Which of the following best describes the percent yield equation?

$$\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$$

Question 1

In the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$, a cylinder contains 14 mol $$H_2$$ and 4 mol $$O_2. $$After the reaction goes to completion, which of the following best describes the contents of the cylinder?

Accepted Answer

8 mol $$H_2O$$ and 6 mol $$H_2$$ remaining

Question 2

A sandwich requires 2 slices of bread and 1 slice of cheese. If you have 160 g of cheese (each slice is 10 g) and 500 g of bread (each slice is 25 g), what is the theoretical yield of sandwiches?

Accepted Answer

16 sandwiches

Question 3

Given the reaction $$6HBr(aq) + Fe_2S_3(s) \rightarrow 2FeBr_3(s) + 3H_2S(g)$$, if you start with 4.24 mol $$Fe_2S_3$$ and 14.5 mol $$HBr$$, which reactant is limiting?

Accepted Answer

$$HBr$$

Question 4

For the reaction $$H_2$$ + $$N_2$$ \rightarrow 2NH_3$$, a cylinder contains 15.12 g H_2$ and 33.62 g N_2$. What is the theoretical yield of NH_3$ in grams?

Accepted Answer

51.3 g

Question 5

In the reaction $$C_2H_6 + Cl_2$ \rightarrow C_2H_5Cl + HCl$$, if you start with 100 g $$Cl_2$$ and 100 g $$C_2H_6$$, and actually produce 150 g $$C_2H_5Cl$$, what is the percent yield?

Accepted Answer

$$75\%$$

Question 6

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

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed

Question 7

If 4.24 mol $$Fe_2S_3$$ and 14.5 mol $$HBr$$ react according to $$6HBr + Fe_2S_3 \rightarrow 2FeBr_3 + 3H_2S$$, how many grams of $$Fe_2S_3$$ remain after the reaction is complete? (Molar mass $$Fe_2S_3 = 207.87 g/$$mol)

Accepted Answer

2.12 mol $$Fe_2S_3$$ remain, which is $$440.7 g$$

Question 8

In a real-world scenario, why is it important to identify the limiting reactant when scaling up a chemical process for industrial production?

Accepted Answer

To maximize the amount of product and minimize waste of excess reactants

Question 9

A reaction has a theoretical yield of 200 g, but only 120 g of product is isolated. What is the percent yield?

Accepted Answer

$$60\%$$

Question 10

In the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$, if you have 10 mol $$H_2$$ and 10 mol $$O_2$$, what is the limiting reactant and how many moles of water are produced?

Accepted Answer

$$H_2 is $$limiting, 10 mol $$H_2O$$ produced

Question 11

Which calculation is necessary to determine the theoretical yield in grams for a reaction?

Accepted Answer

Convert the mass of the limiting reactant to moles, use stoichiometry to find moles of product, then convert to grams

Question 12

If a reaction is performed and the actual yield is greater than the theoretical yield, what is the most likely explanation?

Accepted Answer

The product was contaminated with impurities

Question 13

In the reaction $$N_2 + 3H_2$$ \rightarrow 2NH_3$$, if you start with 10 mol N_2$ and 15 mol H_2$, what is the limiting reactant?

Accepted Answer

$$H_2$$

Question 14

A chemist wants to produce $$C_2H_5Cl$$ using $$C_2H_6$$ and $$Cl_2. If $$the chemist uses 1.0 mol $$C_2H_6$$ and 2.0 mol $$Cl_2$$, what is the maximum number of moles of $$C_2H_5Cl$$ that can be produced?

Accepted Answer

1.0 mol

Question 15

Which of the following is NOT a reason why the actual yield of a reaction is often less than the theoretical yield?

Accepted Answer

All reactants are always completely converted to product

Question 16

In a reaction, the excess reactant is:

Accepted Answer

The reactant that remains after the reaction is complete

Question 17

A student mixes 0.50 mol $$N_2$$ and 1.20 mol $$H_2 to $$produce $$NH_3$$ according to $$N_2 + 3H_2$$ \rightarrow 2NH_3$$. What is the theoretical yield of NH_3$ in moles?

Accepted Answer

Question 18

Which of the following best describes the percent yield equation?

Accepted Answer

$$	ext{Percent Yield} = \frac{	ext{Actual Yield}}{	ext{Theoretical Yield}} 	imes 100\%$$

Limiting Reactants and Theoretical Yields

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