Grade 7 · Physical and Chemical Changes · Changes of State
Heating, Cooling and Particle Motion
What thermal energy does to particles during changes of state.
Learning objectives
- Describe particle motion as thermal energy is added or removed.
- Interpret a heating curve.
- Explain why temperature stays constant during a change of state.
NGSS alignment
MS-PS3-5
Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object.
MS-PS3-4
Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in average kinetic energy of the particles as measured by the temperature of the sample.
MS-PS1-4
Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
Why does a melting ice cube stay at 0 degrees C?
EXPLAIN
Heating curves
When a substance changes state, the energy supplied is used to overcome the forces between particles rather than to increase their speed - so the temperature stays constant.
- Sloping sections: particles gain kinetic energy, temperature rises.
- Flat sections: a change of state, temperature constant.
- Cooling reverses the process exactly.
Interactive simulation · PhET
States of Matter: Basics
Use the heat control and watch the temperature graph during a change of state.
While you explore
- What happens to temperature while a substance is melting?
- Where does the added energy go?
Practice questions
0/1 correct
Level 1
On a heating curve, what does a flat (horizontal) section represent?
Reflect & track
Your learning log
Saved privately in this browser — no account needed.
How confident do you feel?