1.3 Physical and Chemical Properties | Chemistry: Atoms First 2e

Learning Objectives

Identify properties and changes in matter as either physical or chemical
Distinguish between extensive and intensive properties of matter

Core Concepts & Principles (De-Verbosed)

Matter is characterized by specific traits that help us identify, describe, and classify different substances. These characteristics fall into distinct categories based on how they behave and whether they depend on sample size.

Physical Properties and Changes

Physical Property: A characteristic observed or measured without altering the chemical identity of the substance. Common examples include density, color, hardness, melting point, boiling point, and electrical conductivity.
Physical Change: An alteration in the state, form, or appearance of matter that leaves its chemical composition completely unchanged. Examples include melting solid wax, boiling water into steam, dissolving sugar in coffee, or magnetizing a metal.

Chemical Properties and Changes

Chemical Property: A substance's potential (or lack thereof) to undergo a specific chemical transformation. Examples include flammability, toxicity, acidity, and reactivity (such as iron's ability to rust).
Chemical Change: A process that results in the formation of one or more completely new substances with different chemical compositions from the original matter. Examples include burning wood, cooking food, digesting a meal, and metal corrosion.

Extensive and Intensive Properties

Properties of matter are further categorized by how they scale with size:

Extensive Property: Depends directly on the amount of matter present. If you change the amount of substance, the property changes (e.g., mass, volume).
Intensive Property: Does not depend on the amount of matter present. It remains identical regardless of sample size (e.g., temperature, density, color).

Core Mental Model: Matter's Behavior and Scale

Physical changes alter form or phase, keeping chemical structures intact; chemical changes break and form bonds to create brand-new substances.
Intensive properties (like temperature or density) stay constant regardless of sample size; extensive properties (like mass and volume) scale directly with the amount of matter.

Problem-Solving Routines & Methods

How to Classify Properties and Changes

1
Step 1: For a property, ask if measuring it changes the substance's chemical makeup. If NO, it's physical. If it describes reactivity or flammability, it's chemical.
2
Step 2: For a change, ask if a brand-new substance with different chemical formulas is produced. If NO (e.g., phase change, dissolving), it's physical. If YES (e.g., burning, rusting), it's chemical.
3
Step 3: For a property's scale, ask if cutting the sample in half changes the value. If YES, it's extensive. If NO, it's intensive.

Pro-Tip: Students often confuse dissolving with a chemical change. Dissolving sugar in water is a physical change because the sugar molecules remain intact and can be recovered by evaporating the water.

Practice & Concept Checks

Concept Check

Is boiling liquid water to form steam considered a physical change or a chemical change?

Concept Check

Classify mass and density as either intensive or extensive properties.

Key Terms & Vocabulary

Physical PropertyProperties of Matter

A characteristic of matter that is not associated with any change in its chemical composition.

Example: Density, color, hardness, and melting point.

Physical ChangeChanges in Matter

A change in the state or appearance of matter without any accompanying change in its chemical identity.

Example: Melting ice, dissolving sugar, or condensing steam.

Chemical PropertyProperties of Matter

The ability or inability of a substance to change into one or more other types of matter.

Example: Flammability, toxicity, acidity, and iron's ability to rust.

Chemical ChangeChanges in Matter

A change that produces one or more types of matter that differ entirely from the matter present before the change.

Example: Combustion (burning), cooking food, and metal rusting.

Extensive PropertyProperty Classification

A property of matter whose value depends directly on the amount of substance present.

Example: Mass and volume.

Intensive PropertyProperty Classification

A property of matter whose value is independent of the amount of substance present.

Example: Temperature and density.