Question 1

Which of the following best describes the law of conservation of mass?

Accepted Answer

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

Question 2

A student mixes salt (NaCl) in water and observes that the salt dissolves. Which type of change is this, and what evidence supports your answer?

Accepted Answer

Physical change; no new substance is formed and the process is reversible.

Question 3

Given the chemical equation $$\ce{2H_2 (g) + O_2$ (g) \rightarrow 2H_2O (l)}$$, which of the following statements is correct regarding the states of matter?

Accepted Answer

Hydrogen and oxygen are gases, water is a liquid.

Question 4

Which particle diagram best represents a chemical reaction?

Accepted Answer

A diagram where the arrangement of atoms changes, forming new molecules.

Question 5

Which of the following is NOT evidence of a chemical change?

Accepted Answer

Melting of ice into water.

Question 6

Balance the following equation: $$\ce{Fe (s) + Cl_2$ (g) \rightarrow $$FeCl_3$$ (s)}$$

Accepted Answer

$$\ce{2Fe (s) + 3Cl_2 (g) \rightarrow 2FeCl_3 (s)}$$

Question 7

In the equation $$\ce{NaOH (aq) + HCl (aq) \rightarrow NaCl (aq) + H_2O (l)}$$, which substances are reactants?

Accepted Answer

NaOH (aq) and HCl (aq)

Question 8

A student observes that iron rusts when exposed to air, forming iron oxide. Which best describes this process?

Accepted Answer

Chemical change; new bonds are formed and iron oxide is produced.

Question 9

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

Accepted Answer

(aq)

Question 10

A reaction is represented by the equation $$\ce{2K (s) + 2H_2O (l) \rightarrow 2KOH (aq) + H_2$ (g)}. If $$you start with 78 g of K and 36 g of $$H_2O$$, what is the total mass of products formed?

Accepted Answer

114 g

Question 11

Which of the following best distinguishes a chemical change from a physical change?

Accepted Answer

Chemical changes involve breaking and forming bonds, while physical changes do not.

Question 12

Which of the following is a correct match between a chemical equation and its particle diagram?

Accepted Answer

A diagram showing two $$\ce{H_2$}$$ molecules and one $$\ce{O_2$}$$ molecule combining to form two $$\ce{H_2O}$$ molecules matches $$\ce{2H_2 (g) + O_2$ (g) \rightarrow 2H_2O (l)}.$$

Question 13

Which of the following is an example of a physical change?

Accepted Answer

Boiling water to produce steam.

Question 14

In a chemical reaction, which statement about reactants and products is correct?

Accepted Answer

Reactants are the starting substances, products are the substances formed.

Question 15

A student observes a color change and the formation of a gas when two solutions are mixed. What type of change is most likely occurring?

Accepted Answer

Chemical change.

Question 16

Which of the following best explains why the mass of a closed system does not change during a chemical reaction?

Accepted Answer

Atoms are rearranged but not created or destroyed.

Question 17

Which equation is correctly balanced?

Accepted Answer

$$\ce{2Al (s) + 3Br_2 (l) \rightarrow 2AlBr_3 (s)}$$

Question 18

Which of the following statements about the symbols (s), (l), (g), and (aq) in chemical equations is correct?

Accepted Answer

(s) means solid, (l) means liquid, (g) means gas, (aq) means aqueous (dissolved in water).

Question 19

A student is given a particle diagram showing molecules breaking apart and recombining to form new molecules. What type of change does this represent?

Accepted Answer

Chemical change.

Chemical Reactions, Particle Diagrams, and Conservation of Mass

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