Relate temperature to particle motion and absolute zero
Use average kinetic motion and the syllabus's lowest-temperature reference carefully.
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Describe particle motion in different states.
- Distinguish an average from the value for every individual particle.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
If a group's average speed increases, must every individual have an identical speed?
What you will learn
- Relate greater temperature to greater average particle kinetic energy.
- Identify absolute zero as −273°C in the selected syllabus model, with least kinetic energy.
Compare average motion
For a given material in the simple model, increasing temperature is associated with increasing average kinetic energy of its particles. In a solid, this includes stronger vibration; in a gas, particles have faster motion on average. Individual gas particles have different speeds and change them in collisions, so a hotter sample does not mean that every particle has one identical speed.
Compare the same particle type and appropriate conditions. Temperature is not a direct statement of the total energy of an entire sample: amount of material and other energy contributions matter. For example, twice as much gas at the same temperature does not require every particle to move faster. This lesson introduces the kinetic comparison, not a complete internal-energy calculation.
Use the lowest-temperature reference
The selected Cambridge section identifies absolute zero as the lowest possible temperature, −273°C, where particles have least kinetic energy. Use 'least kinetic energy' rather than a universal claim that all motion of every kind ceases. The exact thermodynamic reference is about −273.15°C; the selected syllabus uses −273°C for its school-level conversions and descriptions.
A temperature of −200°C is above −273°C, so it is not below absolute zero. A lower Celsius reading can still be above that lower bound. The kelvin scale and the conversion T = θ + 273 are developed in the following gas-temperature section; they do not change the required idea that absolute zero is the lower-temperature reference.
Sources for this lesson
Pause and explain
Which wording matches the required absolute-zero idea?
Worked example
Compare two samples of the same gas at 20°C and 60°C, then locate −200°C relative to the syllabus's absolute zero.
Show the worked solution
- The 60°C sample has greater average particle kinetic energy.
- This does not assign the same speed to every particle or establish a 3:1 energy ratio.
- −200°C is 73°C above the school-level −273°C reference.
Answer Greater average kinetic energy at 60°C; −200°C is above absolute zero.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare average particle motion for the same gas at 20°C and 60°C without asserting identical individual speeds.
Give me a hint
Use a qualitative average comparison, not a Celsius ratio.
Compare my reasoning
- The 60°C sample is at the higher temperature.
- Its particles have greater average kinetic energy in the simple model.
- Individual speeds remain varied; 60/20 is not an energy-ratio calculation.
Greater average kinetic energy at 60°C; no identical-speed or 3:1 claim.
Look for these in your work
- State the average comparison.
- Avoid unsupported numerical ratios.
State the selected absolute-zero reference and decide whether −200°C and −280°C are above or below it.
Give me a hint
Compare each Celsius reading with −273°C.
Compare my reasoning
- Absolute zero is −273°C in the selected school-level model.
- −200°C is above that reference.
- −280°C is below it and is not a permissible equilibrium temperature in this model.
−273°C, with least kinetic energy; −200°C is above it and −280°C is below the allowed bound.
Look for these in your work
- Compare negative numbers correctly.
- Use the least-energy wording.
Two samples of the same gas have equal temperature, but one contains twice as much gas. A student says its particles must move twice as fast. Correct the claim.
Give me a hint
Distinguish material amount from average particle motion.
Compare my reasoning
- The temperatures are equal.
- The same particle type has the same average kinetic-energy comparison at equal temperature in this model.
- A larger amount does not imply doubled particle speed; total sample energy is a separate account.
Twice the amount does not imply twice the particle speed at equal temperature.
Look for these in your work
- Keep temperature and amount separate.
- Do not equate average motion with total sample energy.
Common mistakes
- Use an average rather than one identical speed.
- Celsius ratios do not directly give kinetic-energy ratios.
- Use least kinetic energy at absolute zero, not a universal no-motion claim.
What can you explain now?
What is absolute zero in this syllabus's school-level description?
Compare with the explanation
−273°C; particles have least kinetic energy.
It is the stated lowest-temperature reference, using the selected approximation.
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Make it stick
Relate temperature to average kinetic motion and use the syllabus's absolute-zero reference without stronger unsupported claims.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.