Specific heat
Heat (q) is energy that flows from a warmer object to a cooler one. It is measured in joules (J). Temperature measures how hot something is. They are related but not the same.
Specific heat (c) is the heat needed to raise the temperature of 1 g of a substance by 1 °C.
q = m × c × ΔT
Here m is the mass in grams and ΔT is the temperature change, final minus initial.
| Substance | Specific heat, J/(g·°C) |
|---|---|
| Water | 4.184 |
| Aluminum | 0.897 |
| Iron | 0.449 |
| Copper | 0.385 |
Water’s specific heat is unusually high. It takes a lot of energy to warm water, which is why lakes change temperature slowly.
Worked example: warming water
How much heat is needed to warm 50.0 g of water from 20.0 °C to 45.0 °C?
ΔT = 45.0 - 20.0 = 25.0 °C
q = 50.0 g × 4.184 J/(g·°C) × 25.0 °C = 5230 J
Common mistake
Using the final temperature in place of ΔT. Only the change matters. If the substance cools, ΔT and q are negative, meaning heat was released.