Temperature and heat
Temperature tells us how hot or cold something is. It is related to the average kinetic energy of its particles: the hotter the object, the faster its particles move. Heat is energy that flows from a hotter object to a colder one. Heat is measured in joules; temperature in degrees Celsius (°C) or kelvin (K).
Thermometers and scales
A liquid-in-glass thermometer works because the liquid expands as it is heated. It is calibrated with two fixed points: the lower fixed point (ice point, 0 °C, the temperature of pure melting ice) and the upper fixed point (steam point, 100 °C, the temperature of steam above boiling pure water at normal pressure). The space between is divided into 100 equal steps.
| Thermometer | Liquid / device | Good for |
|---|---|---|
| Mercury | mercury | wide range, accurate |
| Alcohol | coloured alcohol | very low temperatures |
| Clinical | mercury with a kink | body temperature (35 – 42 °C) |
| Digital | electronic sensor | quick readings |
Change the temperature and watch the liquid rise. Notice the kelvin value.
Normal body temperature is 37 °C. Express it in kelvin.
- Add 273.
Answer: 310 K
Key terms
- Temperature
- How hot something is; related to the average kinetic energy of its particles.
- Heat
- Energy transferred because of a temperature difference.
- Fixed points
- Reference temperatures used to calibrate a thermometer.
Summary
- Temperature measures hotness; heat is energy transferred.
- Thermometers use fixed points: ice point 0 °C and steam point 100 °C.
- T(K) = θ(°C) + 273.