Chapter 3 · Matter and Energy
3.11Temperature Changes: Heat Capacity
11 min · two checks
Predict
Why does a metal pan heat up faster on the stove than the same mass of water?
The idea
- Define heat capacity and specific heat capacity.
- Explain why water changes temperature slowly.
Heat is energy transferred because of a temperature difference. Heat capacity, C, is the energy needed to raise a particular object’s temperature by 1 °C (or 1 K). A large pot has a larger heat capacity than a small one of the same material. Specific heat capacity, c, is that quantity per gram, so different sizes can be compared. The relationship is q = m c ΔT, where ΔT is the temperature change and q is the heat absorbed.
Liquid water has an unusually large specific heat, 4.184 J/(g·°C). Metals are often near 0.1 to 0.9 J/(g·°C). That is why coastal climates are milder than inland ones, and why you can burn your hand on a baking sheet while the water in a pot of similar mass is only warm. Same energy in, smaller c, larger ΔT. When the object cools, q is negative if you take the object as the system: it released heat.
Keep these
- q = m c ΔT.
- Specific heat is per gram; heat capacity is for the whole object.
- Water’s specific heat is 4.184 J/(g·°C), large compared with metals.