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5.3.3Chemical Energetics

Temperature — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 9 of 12 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Temperature and Energy

5.3.3 Temperature

Temperature describes how hot an object is, and it is linked to the motion of its particles.

Temperature
  • A measure of how hot an object is, which is linked to the average kinetic energy of its particles.
Thermal energy
  • The total energy of all the particles in an object, which depends on the mass as well as the temperature.
Heat flow
  • Energy flows from a hotter object to a cooler one until the two reach the same temperature.
Thermal equilibrium
  • When two objects are at the same temperature, there is no further net transfer of energy between them.

Part 2 of 5Measuring Temperature

Different thermometers use different physical properties that change with temperature.

Measuring Temperature
Liquid-in-glass
  • The liquid in a thermometer expands as it warms, and the length of the column shows the temperature.
Thermocouple
  • Two different metals joined together produce a voltage that changes with temperature, useful at high temperatures.
Resistance thermometer
  • The electrical resistance of a metal changes with temperature, so a meter can display the temperature.
Calibration
  • Fixed points, such as the melting point of ice and the boiling point of water, define the scale on a thermometer.

Part 3 of 5Using Kelvin

Kelvin is the correct scale for ratios and for gas law calculations.

1
Use kelvin in equations that involve ratios of temperature, because a ratio in Celsius has no physical meaning.
2
Convert a temperature from degrees Celsius to kelvin by adding 273 to the Celsius value.
3
Find the size of a temperature change by subtracting the two values, which is the same in kelvin and in degrees Celsius.
4
Remember that 0 °C corresponds to 273 K, not to 0 K.

Part 4 of 5Worked Example

Question

  • A gas is heated from 27 °C to 127 °C.
  • Give both temperatures in kelvin, and state the temperature rise in kelvin.

  1. 27 °C + 273 = 300 K.
  2. 127 °C + 273 = 400 K.
  3. Temperature rise = 400 K − 300 K = 100 K.

Answer The gas is heated from 300 K to 400 K, a rise of 100 K, which is the same as a rise of 100 °C.

Part 5 of 5Exam Checklist & Tips

5.3.3 – Key Points for the Exam

  • Temperature A measure of how hot an object is, related to the average kinetic energy of its particles.
  • Thermal energy The total kinetic and potential energy of all the particles in an object.
  • Thermal equilibrium The state in which two objects are at the same temperature and no net energy flows between them.
  • Kelvin The SI unit of temperature, starting at absolute zero.
  • Calibration Marking the scale of a thermometer against known fixed points.

Common Mistakes

  • Confusing thermal energy with temperature;
    • a large object can hold more thermal energy than a small one at the same temperature.
  • Calculating ratios of temperatures in Celsius, which gives a meaningless result because the Celsius zero is arbitrary.
  • Stating that heat flows spontaneously from cold to hot; energy flows from hot to cold.
  • Adding 273 to a value that is already in kelvin.

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