5.3.3Chemical Energetics
Temperature — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 5 parts Lesson 9 of 12 Unit quiz
Section 1 of 5Temperature and Energy
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.
Section 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.
Section 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.
Section 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.
- 27 °C + 273 = 300 K.
- 127 °C + 273 = 400 K.
- 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.
Section 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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