Q: A reaction yields 15.0 g of product, but the theoretical yield is 20.0 g. What is the percent yield?

$$\frac{15.0}{20.0} \times 100 = 75\%$$

Q: If 2.0 moles of $$H_2$$ react with 1.0 mole of $$O_2 to $$produce water, how many molecules of $$H_2O$$ are formed? ($$1$$ mole $$= 6.02 \times 10$$^{23}$$ molecules)

$$2.4 \times 10$$^{24}$$ molecules

Q: A chemical reaction has a theoretical yield of 50.0 g, but only 40.0 g is obtained. What is the percent yield?

$$\frac{40.0}{50.0} \times 100 = 80\%$$

Question 1

A balanced chemical equation for the reaction of hydrogen and oxygen to form water is: $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(g). $$What is the mole ratio of $$H_2 to$$ $$O_2$$?

Accepted Answer

2:1

Question 2

In the reaction $$N_2(g) + 3H_2(g$$) \rightarrow 2NH_3(g)$$, if you start with 6 moles of H_2$, how many moles of NH_3$ can be produced (assuming excess N_2$)?

Accepted Answer

4 moles

Question 3

Which statement about volume ratios in a balanced chemical equation is correct for gases at STP?

Accepted Answer

Volume ratios are equal to mole ratios.

Question 4

Given the reaction $$2SO_2(g) + O_2$(g) \rightarrow 2SO_3(g)$$, what is the volume ratio of $$SO_2 to$$ $$SO_3 at $$STP?

Accepted Answer

2:2

Question 5

If 32.0 g of $$O_2$$ reacts with excess $$CH_4$$ according to $$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$, how many grams of CO_2$ are produced? (Molar masses: O_2$ = 32.0 g/$$mol, $$CO_2 = 44.0$ g/mol)

Accepted Answer

44.0 g

Question 6

A reaction yields 15.0 g of product, but the theoretical yield is 20.0 g. What is the percent yield?

Accepted Answer

$$\frac{15.0}{20.0} 	imes 100 = 75\%$$

Question 7

In the reaction $$2KClO_3 \rightarrow 2KCl + 3O_2$$, how many liters of $$O_2$$ gas at STP are produced from 4 moles of $$KClO_3$$?

Accepted Answer

134.4 L

Question 8

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

Accepted Answer

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

Question 9

For the reaction $$C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O$$, if you have 10.0 L of $$C_2H_4$$ and 30.0 L of $$O_2 at $$STP, which is the limiting reactant?

Accepted Answer

Neither, both are in exact stoichiometric ratio.

Question 10

A student mixes 5.0 g of $$Na$$ with 10.0 g of $$Cl_2 to $$produce $$NaCl$$ according to $$2Na + Cl_2$ \rightarrow 2NaCl. $$Which reactant is in excess? (Molar masses: $$Na = 23.0 g/$$mol, $$Cl_2 = 71.0$ g/mol)

Accepted Answer

$$Cl_2$$

Question 11

In a mass-volume stoichiometry problem at STP, which conversion factor is used to relate moles of a gas to its volume?

Accepted Answer

$$22.4 L/$$mol

Question 12

If 2.0 moles of $$H_2$$ react with 1.0 mole of $$O_2 to $$produce water, how many molecules of $$H_2O$$ are formed? ($$1$$ mole $$= 6.02 	imes 10$$^{23}$$ molecules)

Accepted Answer

$$2.4 	imes 10$$^{24}$$ molecules

Question 13

A chemical reaction has a theoretical yield of 50.0 g, but only 40.0 g is obtained. What is the percent yield?

Accepted Answer

$$\frac{40.0}{50.0} 	imes 100 = 80\%$$

Question 14

In the reaction $$2Al + 3Cl_2 \rightarrow 2AlCl_3$$, how many moles of $$Cl_2$$ are needed to react completely with 4 moles of $$Al$$?

Accepted Answer

6 moles

Question 15

Which of the following is NOT a correct interpretation of a balanced chemical equation?

Accepted Answer

The coefficients represent the ratio of masses of each substance.

Question 16

A reaction produces 67.2 L of $$O_2 at $$STP. How many moles of $$O_2 is $$this?

Accepted Answer

3.0 moles

Question 17

In a real-world scenario, a hospital uses $$O_2$$ for patients. If a tank contains 44.8 L of $$O_2 at $$STP, how many grams of $$O_2$$ does it contain? ($$O_2$$ molar mass = 32.0 g/mol)

Accepted Answer

64.0 g

Question 18

A chemical plant produces ammonia by the reaction $$N_2 + 3H_2$$ \rightarrow 2NH_3$$. If the plant starts with 1000 L of N_2$ and unlimited H_2$, how many liters of NH_3$ can be produced at STP?

Accepted Answer

2000 L

Question 19

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

Accepted Answer

The reactant that remains after the reaction is complete.

Chemical Equation Calculations: Stoichiometry and Interpretation

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