Understanding Specific Heat Capacity

230C

1kg of water

A 1kg of of water water

B 4kg

Figure below shows three objects with different heat capacities because different amounts of heat are required to raise their temperature by 10C. 2kg Al

10C increase in temperatur e

4kg Al

10C increase in temperature

3600 J of heat 1800 J of heat

4kg Pb

10C increase in temperature

520 J of heat

Although A and B are both made from aluminium, they have different heat capaties because the masses are different.

It is because the metal and plastic have different heat capacity

The specific heat capacity of a substance is the amount of heat that must be supplied to increase the temperature 10C for a mass of 1kg of the substance

The formula for specific heat capacity is given by

Therefore, the quantity of heat absorbed or lost from a body is given by

Some substances have higher specific heat capacities than others. Table below lists the specific heat capacities of some common Substance Solids Ice (at -15°C) Aluminium Glass Iron Copper Silver Lead Liquids Water (at 15°C) Ethyl alcohol Benzene Gas Steam

Specific heat capacity, c (J.kg-1°C1) 2000 900 840 452 387 235 128 4200 2450 2410 2010

How much heat energy required to raise the temperature of a 3kg sheet of glass from 240C to 360C? -1 -1 Specific capacity of glass = 840 J Kg C . Answer :

Given m= 3kg change in temperature =36-24=120C Using Q= mcθ Heat energy required, Q Q= mcθ = 3 x 840 x 12 = 30 240 J

The bulb of a thermometer contains 3.4g mercury. What amount of heat required to raise the temperature of the mercury from 300C to 1000C?

Answer: 33 J

When an object is heated by an electrical heater of power, P ,over a period of time, t, the amount of heat energy supplied is given by Q=Pt The formula Q = mcθ become Pt = mcθ