Q: What is the percent composition by mass of oxygen in $$H_2SO_4$$? (Atomic weights: H = 1.0, S = 32.1, O = 16.0)

$$\frac{4 \times 16.0}{98.1} \times 100 = 65.2\%$$

Question 1

Which statement best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

What is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 3

Why are coefficients used instead of changing subscripts when balancing chemical equations?

Accepted Answer

Changing subscripts alters the identity and properties of the compounds.

Question 4

Which of the following is a decomposition reaction?

Accepted Answer

$$CaCO_3 (s$$) \rightarrow CaO (s) + $$CO_2 (g$$)$$

Question 5

A compound has an empirical formula of $$CH_2$$ and a molar mass of $$56 \ g/mol. $$What is its molecular formula?

Accepted Answer

$$C_4H_8$$

Question 6

What is the percent composition by mass of oxygen in $$H_2SO_4$$? (Atomic weights: H = 1.0, S = 32.1, O = 16.0)

Accepted Answer

$$\frac{4 	imes 16.0}{98.1} 	imes 100 = 65.2\%$$

Question 7

How many molecules are present in $$18.0 \ g of $$water ($$H_2O$$)? (Molar mass of $$H_2O = 18.0 \ g/mol)$$

Accepted Answer

$$6.02 	imes 10$$^{23}$$

Question 8

Which of the following is the correct formula weight (FW) of glucose ($$C_6H_{12}O_6$)? (Atomic weights: C = 12.0, H = 1.0, O = 16.0)

Accepted Answer

$$180.0 \ amu$$

Question 9

A sample contains $$3.00 \ g of $$copper ($$Cu). $$How many atoms of copper are present? (Atomic weight of Cu = $$63.5 \ g/mol$$, Avogadro's number $$= 6.02 	imes 10$$^{23}$$)

Accepted Answer

$$2.85 	imes 10$$^{22}$$

Question 10

In a combustion analysis, a $$1.00 \ g$$ sample of an organic compound produces $$2.20 \ g of$$ $$CO_2$$ and $$0.90 \ g of$$ $$H_2O. $$What is the mass of carbon in the sample? (Molar mass of $$CO_2 = 44.0$$ \ g/mol$$, C = 12.0)

Accepted Answer

$$0.60 \ g$$

Question 11

Which reactant is the limiting reactant when $$10.0 \ mol of$$ $$H_2$$ reacts with $$7.0 \ mol of$$ $$O_2 to $$form water?

Accepted Answer

$$H_2$$

Question 12

If $$1.00 \ g of $$glucose ($$C_6H_{12}O_6$) is completely combusted, how many grams of water are produced? (Molar mass of glucose = 180.0$$ \ g/mol$$, C_6H$$_{12}$$O_6 + 6O_2$$ \rightarrow 6CO_2 + 6H_2O$$)

Accepted Answer

$$0.60 \ g$$

Question 13

A reaction has a theoretical yield of $$5.00 \ g$$ but only $$3.50 \ g of $$product is obtained. What is the percent yield?

Accepted Answer

$$70\%$$

Question 14

Which of the following is a combination reaction?

Accepted Answer

$$N_2 (g) + 3H_2 (g$$) \rightarrow 2NH_3 (g)$$

Question 15

What is the empirical formula of a compound containing 61.31% C, 5.14% H, 10.21% N, and 23.33% O by mass?

Accepted Answer

$$C_7H_7NO_2$$

Question 16

Which statement about combustion reactions is correct?

Accepted Answer

Combustion reactions always produce $$CO_2$$ and $$H_2O$$ when burning compounds containing C and H.

Question 17

Which symbol in a chemical equation indicates that a substance is dissolved in water?

Accepted Answer

$$(aq)$$

Question 18

A metal carbonate decomposes when heated. What are the products?

Accepted Answer

A metal oxide and carbon dioxide

Chapter 3: Chemical Reactions and Reaction Stoichiometry – Study Notes

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