Q: Which equation correctly represents the law of conservation of mass for a chemical reaction?

$$\mathrm{\text{Total mass of reactants} = \text{Total mass of products}}$$

Question 1

Which of the following best describes a chemical change?

Accepted Answer

A substance reacts with another to form a new compound, such as iron rusting to form iron oxide.

Question 2

Which of the following is the correct balanced chemical equation for the combustion of methane ($$\mathrm{CH_4$}) in $$oxygen?

Accepted Answer

$$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$

Question 3

Stoichiometry is best defined as:

Accepted Answer

The numerical relationships between reactants and products in a balanced chemical reaction.

Question 4

In the reaction $$\mathrm{2Na + Cl_2$ \rightarrow 2NaCl}$$, how many moles of $$\mathrm{NaCl}$$ are produced from 3 moles of $$\mathrm{Na}$$?

Accepted Answer

3 moles

Question 5

Which of the following is a physical change?

Accepted Answer

Dissolving sugar in water.

Question 6

A student mixes 10.0 g of $$\mathrm{$$CaCO_3$$}$$ with excess $$\mathrm{HCl}$$ and collects 2.2 g of $$\mathrm{CO_2$}$$ gas. If the theoretical yield of $$\mathrm{CO_2$} is 4.4 g$$, what is the percent yield?

Accepted Answer

$$50\%$$

Question 7

Which statement about limiting reactants is correct?

Accepted Answer

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

Question 8

Which of the following is a representative chemical reaction for a Group 1A (alkali metal)?

Accepted Answer

$$\mathrm{2Na + 2H_2O \rightarrow 2NaOH + H_2$}$$

Question 9

If 5.0 g of $$\mathrm{Al}$$ reacts with 10.0 g of $$\mathrm{O_2$} to $$form $$\mathrm{Al_2O_3}$$, which reactant is limiting? (Molar masses: $$\mathrm{Al} = 27.0 g/$$mol, $$\mathrm{O_2$} = 32.0 g/$$mol)

Accepted Answer

$$\mathrm{Al}$$

Question 10

Which equation correctly represents the law of conservation of mass for a chemical reaction?

Accepted Answer

$$\mathrm{	ext{Total mass of reactants} = 	ext{Total mass of products}}$$

Question 11

Which of the following is a balanced chemical equation for the reaction of potassium with chlorine?

Accepted Answer

$$\mathrm{2K + Cl_2$ \rightarrow 2KCl}$$

Question 12

A chemical reaction is represented by $$\mathrm{2H_2 + O_2$ \rightarrow 2H_2O}. If $$you start with 4 moles of $$\mathrm{H_2$}$$ and 2 moles of $$\mathrm{O_2$}$$, how many moles of $$\mathrm{H_2O}$$ can be formed?

Accepted Answer

4 moles

Question 13

Which of the following best describes the process of combustion?

Accepted Answer

A reaction in which a substance combines with oxygen to produce energy and oxygen-containing compounds.

Question 14

What is the theoretical yield of $$\mathrm{CO_2$} (in $$grams) when 10.0 g of $$\mathrm{C_2H_5OH} ($$ethanol, molar mass = 46.0 g/mol) is combusted completely? ($$\mathrm{C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O}$$, molar mass of $$\mathrm{CO_2$} = 44.0 g/$$mol)

Accepted Answer

19.1 g

Question 15

Which of the following is a representative chemical reaction for a Group 7A (halogen)?

Accepted Answer

$$\mathrm{Cl_2$ + 2KBr \rightarrow 2KCl + Br_2$}$$

Question 16

A reaction has a theoretical yield of 5.0 g and an actual yield of 4.0 g. What is the percent yield?

Accepted Answer

$$80\%$$

Question 17

Which of the following statements about chemical equations is correct?

Accepted Answer

Coefficients in a chemical equation indicate the relative number of moles of each substance.

Question 18

If 2.0 moles of $$\mathrm{H_2$}$$ react with 1.0 mole of $$\mathrm{O_2$} to $$form water, which reactant is in excess?

Accepted Answer

$$\mathrm{H_2$} is in $$excess

Question 19

Which of the following is NOT a chemical change?

Accepted Answer

Evaporation of water

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