# Heat & Thermodynamics — ACT Science
Heat and temperature are common themes in ACT Science passages. Experiments may involve heating/cooling curves, specific heat comparisons, and heat transfer methods. Understanding basic thermodynamic concepts helps you interpret data correctly.
Key Concepts
Temperature vs. Heat
- Temperature: measure of average kinetic energy of particles.
- Heat: transfer of thermal energy from hot to cold.
- They are related but different! A large lake at 20°C has more thermal energy than a cup of water at 80°C.
Heat Transfer Methods
- Conduction: through direct contact (e.g., metal spoon in hot soup).
- Convection: through fluid movement (e.g., hot air rising).
- Radiation: through electromagnetic waves (e.g., sunlight).
Specific Heat
- Different materials heat up at different rates.
- Water has a very high specific heat — it heats up and cools down slowly.
- Metals have low specific heat — they heat up quickly.
Phase Changes
- Melting, boiling, freezing, condensation.
- During a phase change, temperature remains constant while energy is absorbed or released.
Heating/Cooling Curves
- Sloped regions: temperature changing.
- Flat regions: phase change occurring.
Worked Example
Passage summary: Equal masses of water and oil are heated with the same energy source.
| Time (min) | Water Temp (°C) | Oil Temp (°C) |
|---|---|---|
| 0 | 20 | 20 |
| 5 | 30 | 45 |
| 10 | 40 | 70 |
| 15 | 50 | 95 |
Q: Which substance has a higher specific heat?
A: Water. It requires more energy to raise its temperature, so it heats up more slowly.
Practice Questions
1. During boiling, what happens to the temperature of water?
It stays constant at 100°C (at standard pressure) until all the water has changed to steam.
2. A metal rod and a wooden rod are both at room temperature. The metal feels colder. Why?
Metal conducts heat away from your hand faster than wood, making it feel colder even though both are the same temperature.
3. On a heating curve, a flat region at 0°C for water represents what process?
Melting (ice → water). The energy is used to break bonds rather than increase temperature.
Want to check your answers and get step-by-step solutions?
Summary
- Heat flows from hot to cold. Temperature measures average particle KE.
- Three modes: conduction, convection, radiation.
- High specific heat → heats slowly (water). Low specific heat → heats quickly (metals).
- Phase change plateaus on heating curves: temperature stays constant.