Every substance is made of particles that are constantly jiggling around — vibrating in a solid, sliding past each other in a liquid, or zooming freely in a gas. Heat energy is just the total kinetic and potential energy tied up in all that jiggling.
When you pump heat energy into a substance, the particles move faster on average. We measure "how fast the particles are moving on average" using temperature. So more heat in → faster particles → higher temperature. Simple so far.
But here's the catch that trips people up: not every substance heats up at the same rate for the same energy input. Give copper and water the exact same amount of energy, and copper's temperature will shoot up while water barely warms at all. Why? Because different materials have different molecular structures — different numbers of ways their particles can store energy (vibrating, rotating, bond-stretching etc.), and different strengths of intermolecular bonds. Water is unusually good at "soaking up" energy without its temperature rising much — this is exactly what specific heat capacity measures.
Real-world analogy
Think of specific heat capacity like the size of a bucket. A big bucket (water, c = 4200) needs a lot of water poured in before the level (temperature) rises noticeably. A small bucket (copper, c = 390) fills up — and its level rises — much faster for the same pour. That's why a metal spoon in hot tea gets hot almost instantly, but the tea itself stays hot for ages.
Definition to know word-for-word: Specific heat capacity is the energy required to raise the temperature of one kilogram of a substance by one kelvin.
The temperature rise of an object heated by a certain amount of energy depends on three things:
- The amount of heat energy transferred to it
- The mass of the object (more mass = more particles to speed up = smaller temperature rise for the same energy)
- The specific heat capacity of the material it's made from
Watch out
Δθ is a change in temperature, so it's the same numerical value whether you work in kelvin or Celsius (a 5 K rise = a 5 °C rise). Don't waste time converting Celsius to Kelvin for Δθ — you only need to convert if you're given an absolute temperature, not a change.
| Substance | Specific Heat Capacity (J kg⁻¹ K⁻¹) |
|---|
| Water | 4200 |
| Ice | 2200 |
| Aluminium | 900 |
| Copper | 390 |
| Gold | 130 |
Good electrical conductors like copper are also excellent conductors of heat because their free electrons transfer energy quickly, and they tend to have low specific heat capacities — they warm up and cool down fast. Water's very high specific heat capacity is exactly why it's used in radiators: it stores huge amounts of energy and releases it slowly, keeping a room warm for a long time.
Water of mass 0.48 kg is increased in temperature by 0.7 K. The specific heat capacity of water is 4200 J kg⁻¹ K⁻¹. Calculate the energy transferred.
Step 1 — List knowns: m = 0.48 kg, Δθ = 0.7 K, c = 4200 J kg⁻¹K⁻¹
Step 2 — Write the equation: ΔE = mcΔθ
Step 3 — Substitute: ΔE = 0.48 × 4200 × 0.7 = 1411.2
Step 4 — Round sensibly: ΔE ≈ 1400 J