Lesson focus: temperatureA measure of how hot an object is, which depends on the average kinetic energy of its particles; it is measured in °C and is not the same as thermal energy. measures particle energy statistically, while internal energyThe total energy of all the particles in an object, from their movement and the forces between them. depends on both particle number and particle energies.
Distinguish temperature, internal energy and energy transfer by heatingWhen energy moves from a hotter object to a cooler one..
Build on earlier learning
Melting and freezingYear 7 used particle motion to explain temperature; this lesson separates temperature from total internal energy.
Practical
Heating water
- Heat different masses of water with the same heater for the same time.
- Record each temperature rise.
- Use the model on this page to see how mass and energy affect the temperature rise.
Record: A table of mass against temperature rise.
Heating water
Choose the mass of water and the energy supplied by the heater. The temperature rise = energy ÷ (mass × 4200).
Controls
Assumes no energy is lost to the surroundings.
You will be successful when you can…
- Define temperature at particle level.
- Describe internal energy.
- Explain heating direction.
- Interpret heating-water data.
Words that carry the science
- temperature
- A measure related to the average kinetic energy of particles.
- internal energy
- The total kinetic and potential energy of particles in a system.
- heating
- Energy transfer caused by a temperature difference.
- thermal equilibrium
- State in which objects in contact have the same temperature and no net heating occurs.
- joule
- The SI unit of energy.
Temperature is an average
01Temperature is an average
temperatureA measure of how hot an object is, which depends on the average kinetic energy of its particles; it is measured in °C and is not the same as thermal energy. relates to the average kinetic energy of particles. Faster average random motion corresponds to higher temperatureA measure of how hot an object is, which depends on the average kinetic energy of its particles; it is measured in °C and is not the same as thermal energy..
Temperature does not tell us the total energy stored. A mug of hot water can have a higher temperature but less internal energyThe total energy of all the particles in an object, from their movement and the forces between them. than a warm bath.
02Internal energy depends on the whole system
Internal energy is the total kinetic and potential energy of all particles in the system. It depends on particle number, temperature, state and substance.
During melting or boiling, energy can increase particle potential energy while temperature stays nearly constant for a pure substance at fixed pressure.
03Heating follows a temperature difference
Net energy transfer by heating occurs from higher temperature to lower temperature until thermal equilibriumWhen two objects touching are at the same temperature, so no more heat flows between them. is approached.
For the same substance and temperature rise, a larger mass needs more energy because more particles contribute to the internal-energy change.
Compare a mug and bath
A 0.25 kg mug of water is at 80 °C. A 100 kg bath is at 35 °C.
- Compare temperature: the mug has the higher average particle kinetic energy.
- Compare mass: the bath contains far more water particles.
- Internal energy depends on all particles, not temperature alone.
- Without full reference data an exact comparison is not calculated, but the bath can have much more internal energy.
How to make the reasoning visible: Higher temperature does not automatically mean greater total internal energy.
Heating-water
Compare idealised equal-power trials.
| Water mass / g | Start / °C | After 120 s / °C | Rise / °C |
|---|---|---|---|
| 100 | 20 | 44 | 24 |
| 200 | 20 | 32 | 12 |
| 300 | 20 | 28 | 8 |
| 100 | 30 | 54 | 24 |
What pattern links mass and temperature rise?
What does the final row show?
Check your understanding
Answer from memory, then check against the suggested answer.
What does temperature measure?
What is internal energy?
Direction of net heating?
Why can a swimming pool at 28 °C store more internal energy than a cup at 90 °C?
Why can energy transfer continue during boiling without a temperature rise?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
200 g of water and 100 g of water each receive the same amount of energy.
Explain why the 200 g sample warms less. Use ideas about particles.
(5)Total for this question: 5 marks
Command word: Build a particle-level chain from mass to energy per particle and then to temperature.