L3. Physical and Chemical Properties

Matter and Measurement

R-report

L3. Physical or Chemical?

How do you know whether something changed or a new substance was made?

Observe and name:

A physical property describes how a substance looks or behaves without changing what it is; a chemical property describes how a substance can react to form one or more new substances. To use these ideas, first observe carefully and record what you can measure (color, state, mass, volume, melting point, density), then ask questions that separate an observation from an explanation. Ask three quick questions as you work: Does the identity of the substance change?, Are atoms or bonds rearranged?, Can the change be reversed by physical means? Answering these helps you decide whether you are dealing with a physical property or a chemical property.

Analyze like a scientist:

1) Name the items involved and list the observable properties (for example: wax — white solid, melts at 60 °C, density 0.95 g/cm³). 2) Separate pure observations (color, melting, mass) from explanations (it melted because molecules moved faster). 3) Identify relationships: does a new substance appear (smell of new gas, permanent color change, solid forming from two solutions)? Ask: could I get the original back by cooling, filtering, evaporating, or would I need a chemical reaction? Reflect with short tests (measure mass before and after, measure volume to compute density in g/cm³, and watch for bubbles or heat that indicate a chemical change).

Try comparisons and tests:

Move the idea to new situations by comparing what stays the same and what changes. When you test a material, vary one thing at a time: change the material (different metals, salts, or plastics), change the amount (mass or volume), or change the temperature (hot vs cold). Look specifically at density (calculate density = mass ÷ volume with units, e.g., 12.0 g ÷ 4.0 cm³ = 3.0 g/cm³), color, state (solid/liquid/gas), and melting point as examples of physical properties. For chemical properties try flammability or how a substance reacts with oxygen (for example, iron + oxygen → rust over time); chemical tests often produce new substances, heat, light, or gas.

Tie words to observations:

When you name a property (density, melting point, flammability) you link a simple observation to a stronger explanation. For example, measuring mass (g) and volume (cm³) and computing density (g/cm³) gives a number you can compare to known values; noticing bubbles, a permanent color change, or a new solid points to rearranged atoms and a chemical change. Using the correct vocabulary lets you predict what might happen next: a substance with high flammability will burn in air, while a high melting point means the solid stays solid at room temperature.

Checklist before you conclude: make sure units agree (mass in g, volume in cm³), tell the particle-level story (atoms same or rearranged), and match evidence to the claim (reversible physical process vs permanent chemical change). When you perform simple tests, write the steps and results so others can repeat them.