Chemical Properties: Definitions, Examples, and Applications

Chemical Properties

Definition and Overview

Chemical properties are characteristics of a substance that become evident during or after a chemical reaction. These properties describe the ability of a substance to undergo specific chemical changes, resulting in the formation of new substances with different compositions and properties.

• Definition: A property of matter that is observed during a chemical reaction.

• After a chemical reaction, the original matter is transformed into a new substance.

Example of a chemical reaction:

$2\ \mathrm{CH}_3\mathrm{OH}\ (g) + 3\ \mathrm{O}_2\ (g) \rightarrow 2\ \mathrm{CO}_2\ (g) + 4\ \mathrm{H}_2\mathrm{O}\ (g)$

Common Chemical Properties

Chemical properties are used to describe how substances interact with other chemicals. Some of the most important chemical properties include:

Chemical Property	Description	Example
Flammability	Ability to catch fire and burn in the presence of oxygen	Gasoline is highly flammable
Toxicity	Degree to which a substance can harm living organisms	Mercury is toxic to humans
Corrosion	Ability to be gradually destroyed by chemical reactions, often with oxygen or acids	Iron rusts when exposed to moisture and oxygen
Reactivity	Tendency to undergo chemical reactions, either by itself or with other materials	Sodium reacts explosively with water
Radioactivity	Ability to emit radiation as a result of changes in the atomic nucleus	Uranium is radioactive
Acidity	Ability to donate protons (H+) in a chemical reaction	Hydrochloric acid is highly acidic

Identifying Chemical Properties

• Chemical properties are not observed by simply viewing or touching a substance; they are observed when the substance undergoes a chemical change.

• Examples of chemical changes include burning, rusting, decomposing, and reacting with acids or bases.

Example Question

Question: Which of the following is not a chemical property for an unknown element?

1. It has a yellow-orange color. (Correct answer: This is a physical property, not a chemical property.)

2. It is very soluble in an acid solution.

3. It is radioactive.

4. It experiences rusting when exposed to pure oxygen gas.

5. It has a high reactivity with acids.

Explanation: Color is a physical property because it can be observed without changing the substance's chemical identity. The other options describe how the substance interacts chemically with other substances or undergoes chemical changes.

Practice Question

Question: Which of the following represents a chemical property of hydrogen gas?

1. It exists as a gas at room temperature. (This is a physical property.)

2. It is less dense than air. (Physical property)

3. It reacts explosively with oxygen gas. (Correct answer: This is a chemical property.)

4. It is a colorless gas. (Physical property)

5. It is a tasteless molecule. (Physical property)

Explanation: The ability of hydrogen gas to react explosively with oxygen is a chemical property because it describes a chemical change resulting in the formation of water.

Summary Table: Physical vs. Chemical Properties

Physical Properties	Chemical Properties
Color, density, melting point, boiling point, state of matter	Flammability, reactivity, toxicity, acidity, radioactivity
Can be observed without changing the substance's identity	Observed only when a substance undergoes a chemical change