Specific Heat Capacity

Hot Vs Cold

Heat Vs Temperature

In Physics, heat is: the flow of energy from a region of higher temperature to a region of

lower temperature

• Conduction• Convection• Radiation

The Temperature of a body is a measure of the mean, random, kinetic energy of its vibrating atoms

• Heat is a flow of energy, but the idea that heat is something contained in a body is wrong. What a body does have is internal energy.

• This is made up of the potential energy contained within the inter-atomic bonds and the kinetic energy of the vibrations of the atoms.

• They are being continuously stretched and compressed as the atoms vibrate – rather like springs.

• The kinetic energy depends on the temperature - the hotter a body is, the more rapidly its atoms vibrate and so the greater their kinetic energy becomes.

• Units of Temperature• SI unit is Kelvin (K)• It is defined in terms of what is called the

absolute thermodynamic scale of temperature, which has absolute zero as its zero and defines the melting pt of ice as 273K

TEMPERATURE

• θ is given to a temperature recorded in oC• T if the temperature is in K• Absolute zero (0K) corresponds to a

temperature of approximately -273oC

• T/K = θ/oC + 273

Temperature oC K

Absolute zero -273 0

Ice point of water 0 273

Boiling point of water 100 373

Element oC K

Aluminium 2350

Argon -186

Copper 2853

Helium 4

Specific Heat Capacity

• The property of a material that quantifies this is called its specific heat capacity, which is given the symbol, c.

• If we had m kg of the material and we raised its temperature by ∆T K, the energy needed would be:

• ∆E=mc∆T

• c = ∆E/m∆T, what are the units?• c has the units Jkg-1K-1

Material Specific Heat Capacity/ Jkg-1K-1

Copper 390

aluminium 910

water 4200

• An aluminium saucepan of mass 400g containing 750g of water, is heated on a gas hob. How much energy would be required to bring the water from room temperature of 18oC to the boil?

• An electric kettle rated at 2.1kW contains 1.2kg of water at 25oC. Calculate how long it will take for the water to come to the boil. Explain why it will actually take longer than you have calculated?