Calculating Heat

Specific Heat

Amount of heat energy needed to raise the temp of 1 ml of a substance 1°C

For water the specific heat is 4.19 J/g °C, but it is differenct for different substances

It takes 4.19 J to raise the temp of 1 g of water 1 °C

Every substance has a different specific heat

Table of Specific Heats

Calculating Heat When Substance in One Phase

Heat released or absorbed can be calculated by multiplying three factors

Heat = specific heat x mass x temp change

q = c x m x Δt

Practice

The specific heat of water is 4.19 J/ g C. How much heat is needed to warm 350g of water from 25 C to 75 C?

If 178 J of heat is needed to increase the temperature of a 20g piece of copper metal from 25 C to 48 C, what is the specific heat of copper?

Heat and Phase Change (Evaporation)

Heat of vaporization (Hvao) energy required to change one gram of a substance from liquid to gas.

For water 2260J/g Q = Hvao m

Practice

The heat of vaporization of water is 2260J/g. How much heat must be supplied to evaporate 50g of water?

How much heat is required to evaporate 150.g of a substance at its boiling point if it has a Hvap= 987 J/g?

Energy and Phase Change

Heat of fusion (Hfus) energy required to change one gram of a substance from solid to liquid.

For water 340 J/g Q = Hfus m

Examples

The heat of fusion of ice at 0°C is 340J/g. How much heat is needed to change 75g of ice at 0°C to a liquid at the same temperature?

The heat of fusion of water at 0°C is 340J/g. How much heat is released when 250g of water changes to ice at 0°C?

Practice

How much heat is needed to change 100g of water at 50C to steam at 120C? The specific heat of water is 4.19 J/g C, the specific heat of steam is 1.7 J/g C, and the heat of vaporization of water is 2260 J/g.

How much heat must be released as 50g of water at 25C to ice at -10C? The specific heat of water is 4.19 J/g C, the specific heat of ice is 2.1 J/g C, and the heat of fusion fro water is 340 J/g.