ChemAtlas

Chapter 6

Heat and energy

Heating something raises its temperature. Melting or boiling it does not — all the energy goes into breaking the forces between particles, which is why a heating curve has flat steps.

Conversion

1 cal = 4.184 J

A food Calorie is 1000 of these

°Cheat added →Melting · 0 °CBoiling · 100 °CLiquid warmsIce warmsSteamq = m·ΔHq = m·ΔHq = mcΔT
Fig. 7Temperature stalls while a phase changes. All the energy is going into breaking the forces between molecules, not into making them move faster.
Solve for
J
g
J/(g·°C)
°C

Why water is different

Water's specific heat of 4.184 J/(g·°C) is unusually high, so it soaks up a lot of energy for a small temperature rise. That is what stops body temperature swinging with every meal, and why coastal weather is mild.

Heat

8368J

2000 cal

In kilojoules

8.368kJ

Working

  1. 01q = m × c × ΔT
  2. 02q = 100 g × 4.184 J/(g·°C) × 20 °C8368 J
  3. 03In calories: 8368 J ÷ 4.184 J/cal2000 cal