Question 1

Which of the following best describes the law that must be followed when balancing chemical equations?

Accepted Answer

The total number of atoms of each element must be the same on both sides of the equation.

Question 2

Balance the following equation for the combustion of methane: $$\mathrm{CH_4$(g) + O_2$(g) \rightarrow CO_2$(g) + H_2O(g)}. $$What is the correct set of coefficients?

Accepted Answer

$$1, 2, 1, 2$$

Question 3

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

Accepted Answer

$$176$$ moles

Question 4

Which of the following is the correct balanced equation for the reaction of aluminum with oxygen to form aluminum oxide?

Accepted Answer

$$4Al(s) + 3O_2(g) \rightarrow 2Al_2O_3(s)$$

Question 5

A reaction has a theoretical yield of $$50.0 g $$and an actual yield of $$37.5 g. $$What is the percent yield?

Accepted Answer

$$75\%$$

Question 6

If $$0.750 g of$$ $$\mathrm{Co_3O_4} ($$molar mass $$240.8 g/$$mol) reacts with $$0.350 g of$$ $$\mathrm{O_2$} ($$molar mass $$32.00 g/$$mol) to form $$\mathrm{Co_2O_3}$$, what is the limiting reactant?

Accepted Answer

$$\mathrm{Co_3O_4}$$

Question 7

Given the reaction $$\mathrm{2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2$(g)}$$, how many grams of $$\mathrm{NaOH} ($$molar mass $$40.00 g/$$mol) are produced from $$4.60 g of$$ $$\mathrm{Na} ($$molar mass $$23.00 g/$$mol)?

Accepted Answer

$$8.00 g$$

Question 8

Which of the following statements about limiting reactants is correct?

Accepted Answer

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

Question 9

In the reaction $$\mathrm{2Li(s) + 2H_2O(l) \rightarrow 2LiOH(aq) + H_2$(g)}$$, how many moles of $$\mathrm{H_2$}$$ are produced from $$5.00$$ mol of $$\mathrm{H_2O}$$?

Accepted Answer

$$2.50$$	ext{ mol}$

Question 10

A student balances the equation $$\mathrm{N_2$(g) + H_2$(g) \rightarrow NH_3$(g)}$$ and finds the coefficient for $$\mathrm{NH_3$} is$$:

Accepted Answer

$$2$$

Question 11

Which of the following best explains why the combustion of fossil fuels is linked to climate change?

Accepted Answer

Combustion of fossil fuels releases $$\mathrm{CO_2$}$$, a greenhouse gas, which increases atmospheric temperatures.

Question 12

Given the reaction $$\mathrm{2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2$(g)}$$, how many moles of $$\mathrm{O_2$}$$ are produced from $$6.00$$ mol of $$\mathrm{H_2O_2}$$?

Accepted Answer

$$3.00$$	ext{ mol}$

Question 13

If $$0.500$$ mol of $$\mathrm{C_8H_{18}}$$ reacts with $$2.00$$ mol of $$\mathrm{O_2$}$$, which is the limiting reactant in the combustion reaction $$\mathrm{2C_8H_{18} + 25O_2 \rightarrow 16CO_2 + 18H_2O}$$?

Accepted Answer

$$\mathrm{O_2$}$$

Question 14

A reaction has a theoretical yield of $$10.0 g $$and an actual yield of $$7.5 g. $$What is the percent yield?

Accepted Answer

$$75\%$$

Question 15

Which of the following is NOT a correct guideline for balancing chemical equations?

Accepted Answer

Subscripts in chemical formulas can be changed to balance the equation.

Question 16

In a mass-to-mass stoichiometry problem, which step must always be performed first?

Accepted Answer

Convert the mass of the given substance to moles.

Question 17

For the reaction $$\mathrm{2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)}$$, how many moles of $$\mathrm{O_2$}$$ are produced from $$4.00$$ mol of $$\mathrm{$$KClO_3$$}$$?

Accepted Answer

$$6.00$$	ext{ mol}$

Question 18

Which of the following best describes the term 'theoretical yield'?

Accepted Answer

The maximum amount of product that can be formed from given reactants, calculated from the balanced equation.

Question 19

In the reaction $$\mathrm{Pb(NO_3$)_2(aq) + 2KI(aq) \rightarrow $$PbI_2$$(s) + 2KNO_3(aq)}$$, what is the coefficient of $$\mathrm{KI}$$ after balancing?

Accepted Answer

$$2$$

Question 20

A student recovers $$1.00 g of$$ $$\mathrm{Ca(OH)_2}$$ from a reaction that theoretically should produce $$1.50 g. $$What is the percent yield?

Accepted Answer

$$66.7\%$$

Chemical Reactions and Chemical Quantities: Balancing, Stoichiometry, and Yield

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