Specific Heat Capacity of Water

What is Specific Heat?

Specific Heat capacity (C) is the amount of heat energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius (or 1 Kelvin).

Think of specific heat as a substance’s ‘thermal inertia.’ A high specific heat means it’s hard to change its temperature, just like a heavy object is hard to move. Water is a thermal heavyweight.

It is an intrinsic property of a material, meaning it depends on the substance’s molecular structure and phase (solid, liquid, gas).

Specific Heat Capacity of Water

Water has one of the highest specific heat capacities among common substances:

Specific Heat of Water (at 20°C, 101.3 kPa):

                                        4.186 J/g·°C | 4186 J/kg·°C | 1 cal/g·°C | 1 Btu/lb·°F

This means it takes 4.186 joules of energy to raise 1 gram of water by 1°C.

Formula for Heat Energy (Q)
The heat energy (Q) required to change the temperature of a substance is given by:

• Example: “How much energy is needed to heat 2 kg of water from 20°C to 100°C?”

  • m = 2000 g, c = 4.186 J/g·°C, ΔT = 80°C

  • Q = 2000 g * 4.186 J/g·°C * 80 °C = 669,760 J (or 669.76 kJ)

What are Isobaric (Cp) and Isochoric (Cv) Specific Heats?

• Cp (Isobaric): The specific heat at constant pressure. This is the most common measurement for everyday processes (e.g., heating water in an open pot).

• Cv (Isochoric): The specific heat at constant volume. This is important for closed, rigid containers where volume cannot change.

• Cp > Cv: Cp is higher because at constant pressure, some energy goes into doing work by expanding the volume, not just raising the temperature.