Q: A reaction yields 42.8 kg of Ti, but the theoretical yield is 52.9 kg. What is the percent yield?

$$\frac{42.8}{52.9} \times 100\% = 80.9\%$$

Q: What is the percent yield formula in chemical reactions?

$$\text{Percent Yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$$

Question 1

Which of the following best describes a physical change in matter?

Accepted Answer

A change that alters only the state or appearance, but not the composition, of a substance.

Question 2

When iron rusts, which type of change occurs and what is the product?

Accepted Answer

Chemical change; iron(III) oxide ($$Fe_2O_3)$$

Question 3

Which statement about chemical equations is FALSE?

Accepted Answer

They do not need to be balanced to obey the law of conservation of mass.

Question 4

Given the reaction $$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(l$$)$$, how many molecules of O_2$ are required to completely react with 3 molecules of CH_4$?

Accepted Answer

6 molecules

Question 5

What is the correct balanced equation for the reaction between solid iron(III) oxide and solid carbon to produce solid iron and carbon dioxide gas?

Accepted Answer

$$Fe_2O_3(s) + 3C(s) \rightarrow 2Fe(s) + 3CO(g)$$

Question 6

In the combustion of octane, $$2C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)$$, how many moles of $$CO_2$$ are produced from 22.0 moles of $$C_8H_{18}$$?

Accepted Answer

176 moles

Question 7

A student combusts 9.0 g of glucose ($$C_6H_{12}O_6$) according to the equation C_6H$$_{12}$$O_6(s) + 6O_2(g$$) \rightarrow 6CO_2(g) + 6H_2O(l)$$. How many milliliters of water are produced? (Molar mass of glucose = 180 g/mol, water = 18.02 g/mol, density of water = 1.00 g/mL)

Accepted Answer

5.4 mL

Question 8

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

Accepted Answer

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

Question 9

In the reaction $$TiO_2(s) + 2C(s$$) \rightarrow Ti(s) + 2CO(g)$$, if 28.6 kg of C and 88.2 kg of $$TiO_2$$ are reacted, which is the limiting reactant? (Molar masses: $$TiO_2$$ = 79.87 g/mol, C = 12.01 g/mol)

Accepted Answer

Titanium dioxide ($$TiO_2)$$

Question 10

A reaction yields 42.8 kg of Ti, but the theoretical yield is 52.9 kg. What is the percent yield?

Accepted Answer

$$\frac{42.8}{52.9} 	imes 100\% = 80.9\%$$

Question 11

In the combustion of methane, $$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(g$$)$$, if you have 5 molecules of CH_4$ and 8 molecules of O_2$, which is the limiting reactant?

Accepted Answer

$$O_2$$

Question 12

Which of the following is TRUE about the actual yield in a chemical reaction?

Accepted Answer

It is generally less than the theoretical yield due to losses during the experiment.

Question 13

What is the percent yield formula in chemical reactions?

Accepted Answer

$$	ext{Percent Yield} = \frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$

Question 14

Which of the following is a combustion reaction?

Accepted Answer

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

Question 15

Which statement about stoichiometry is correct?

Accepted Answer

Stoichiometry is the numerical relationship between chemical quantities in a reaction.

Question 16

If 9.05 g of $$NH_3$$ reacts with 45.2 g of $$CuO$$ according to $$2NH_3(g) + 3CuO(s) \rightarrow N_2$(g) + 3Cu(s) + 3H_2O(l)$$, what is the limiting reactant? (Molar masses: $$NH_3 = 17.03 g/$$mol, $$CuO = 79.55 g/$$mol)

Accepted Answer

$$NH_3$$

Question 17

Which of the following is NOT provided by a chemical equation?

Accepted Answer

The speed at which the reaction occurs.

Question 18

In a reaction, the reactant that remains after the limiting reactant is consumed is called:

Accepted Answer

Excess reactant

Question 19

Which of the following is a correct step in balancing chemical equations containing polyatomic ions?

Accepted Answer

Balance polyatomic ions as units if they appear unchanged on both sides of the equation.

Chapter 7: Chemical Reactions and Chemical Quantities – Study Notes

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