Question 1

Which scientist is most closely associated with the Law of Mass Conservation, which states that the total mass of substances before and after a chemical reaction is equal?

Accepted Answer

Antoine Lavoisier

Question 2

Balance the following reaction: $$\mathrm{Na}(s) + \mathrm{Cl}_2(g) \rightarrow \mathrm{NaCl}(s). $$What are the smallest whole-number coefficients?

Accepted Answer

$$2, 1, 2$$

Question 3

Which of the following best explains why chemical equations must be balanced?

Accepted Answer

To satisfy the Law of Mass Conservation, ensuring the number and type of atoms are the same on both sides.

Question 4

Given the reaction $$2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(l)$$, if you start with 2.00 mol $$\mathrm{H}_2$$ and 1.00 mol $$\mathrm{O}_2$$, what is the mass of water produced? (Molar mass $$\mathrm{H}_2\mathrm{O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

$$36.04\ \mathrm{g}$$

Question 5

Balance the reaction: $$\mathrm{C}_2\mathrm{H}_4(g) + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + \mathrm{H}_2\mathrm{O}(g). $$What is the sum of the smallest coefficients?

Accepted Answer

$$7$$

Question 6

For the reaction $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightarrow 2\mathrm{NH}_3(g)$$, how many moles of $$\mathrm{N}_2$$ are required to react with 1.20 mol $$\mathrm{H}_2$$?

Accepted Answer

$$0.40$$ mol

Question 7

A reaction mixture contains only PbO and PbS. After the reaction $$\mathrm{PbO}(s) + \mathrm{PbS}(s) \rightarrow \mathrm{Pb}(s) + \mathrm{SO}_2(g)$$, there are 18 mol Pb(s), 21 mol PbO(s), and 42 mol PbS(s). How many moles of PbS were present before the reaction?

Accepted Answer

60 mol

Question 8

If 25.0 g of $$\mathrm{N}_2\mathrm{O}_5$$ completely decomposes according to $$2\mathrm{N}_2\mathrm{O}_5(g) \rightarrow 2\mathrm{N}_2(g) + 5\mathrm{O}_2(g)$$, what is the total mass of products formed? (Molar mass $$\mathrm{N}_2\mathrm{O}_5 = 108.02\ \mathrm{g/mol})$$

Accepted Answer

$$25.0\ \mathrm{g}$$

Question 9

How many moles of $$\mathrm{N}_2$$ are formed from 0.231 mol $$\mathrm{N}_2\mathrm{O}_5 in $$the reaction $$2\mathrm{N}_2\mathrm{O}_5(g) \rightarrow 2\mathrm{N}_2(g) + 5\mathrm{O}_2(g)$$?

Accepted Answer

0.231 mol

Question 10

How many moles of $$\mathrm{O}_2$$ are formed from 0.231 mol $$\mathrm{N}_2\mathrm{O}_5 in $$the reaction $$2\mathrm{N}_2\mathrm{O}_5(g) \rightarrow 2\mathrm{N}_2(g) + 5\mathrm{O}_2(g)$$?

Accepted Answer

0.577 mol

Question 11

Solid aluminum reacts with chlorine gas: $$2\mathrm{Al}(s) + 3\mathrm{Cl}_2(g) \rightarrow 2\mathrm{AlCl}_3(s). If a $$large excess of aluminum is added to a sealed flask containing 142 g chlorine, what is the mass of $$\mathrm{AlCl}_3$$ produced? (Molar mass $$\mathrm{Cl}_2 = 70.90\ \mathrm{g/mol}$$, $$\mathrm{AlCl}_3 = 133.34\ \mathrm{g/mol})$$

Accepted Answer

178.12 g

Question 12

Iron(III) oxide reacts with carbon monoxide: $$\mathrm{Fe}_2\mathrm{O}_3(s) + 3\mathrm{CO}(g) \rightarrow 2\mathrm{Fe}(s) + 3\mathrm{CO}_2(g). $$What is the mass of $$\mathrm{CO}_2$$ formed from the reaction of 69 g $$\mathrm{Fe}_2\mathrm{O}_3$$ with excess CO? (Molar mass $$\mathrm{Fe}_2\mathrm{O}_3 = 159.7\ \mathrm{g/mol}$$, $$\mathrm{CO}_2 = 44.01\ \mathrm{g/mol})$$

Accepted Answer

57.1 g

Question 13

Balance the reaction: $$\mathrm{C}_5\mathrm{H}_{12}(g) + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + \mathrm{H}_2\mathrm{O}(g). $$What is the coefficient for $$\mathrm{O}_2$$?

Accepted Answer

8

Question 14

In the reaction $$2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(l)$$, what is the limiting reactant if you start with 2.00 mol $$\mathrm{H}_2$$ and 2.00 mol $$\mathrm{O}_2$$?

Accepted Answer

$$\mathrm{H}_2$$

Question 15

A student claims that balancing a chemical equation is unnecessary because atoms are created during reactions. Which law does this statement violate?

Accepted Answer

Law of Mass Conservation

Question 16

For the reaction $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightarrow 2\mathrm{NH}_3(g)$$, how many moles of $$\mathrm{NH}_3$$ are produced from 1.20 mol $$\mathrm{H}_2$$?

Accepted Answer

0.80 mol

Question 17

If 15.0 g $$\mathrm{O}_2$$ was formed by the decomposition of $$\mathrm{N}_2\mathrm{O}_5$$, and the theoretical yield is 25.0 g, what is the percent yield?

Accepted Answer

60%

Question 18

Which of the following is a real-world use of chlorine, as described in the study materials?

Accepted Answer

Used as a chemical weapon in WWI

Balancing Chemical Reactions and Stoichiometry: Core Concepts and Practice

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