Temperature

Temperature and heat are not the same thing because!!!

• temperature is a measure of how hot something is
• heat is a measure of the thermal energy contained in an object.

Temperature is measured in ºC, and heat is measured in J.

Thermograms

Thermal imaging cameras can detect infrared radiation - the type of radiation emitted by all objects. The images they produce are called thermograms. False colours are added to a thermogram to give an indication of how hot each object in the image is, with:

• the coldest parts are coloured purple, dark blue or black.
• the hottest parts are coloured white, yellow or red

Changing temperatures

Heat energy flows from a hot object to a cooler one. This causes:

• hot objects to cool down
• cool objects to warm up.

When heat energy is transferred to an object, its temperature increase depends upon:

• the mass of the object 
• the substance the object is made from
• the amount energy transferred to the object.

For a particular object, the more heat energy transferred to it, the greater its temperature increase.

Specific heat capacity

The specific heat capacity of a substance is a measure of how much heat energy it can hold.

It is the energy needed to increase the temperature of 1 kg of the substance by 1 ºC.

Different substances have different specific heat capacities.

E = M x C x       T

Energy (J) = mass (kg) × specific heat capacity (J/kg/ºC) × temperature change (ºC)

Specific latent heat

The specific latent heat of a substance is a measure of how much heat energy is needed to melt or boil it.

It is the energy needed to melt or boil 1 kg of the substance.

Different substances have different specific latent heats. The specific latent heat of a given substance is different for boiling than it is for melting. 

E = M x SLH

energy (J) = mass (kg) × specific latent heat (J/kg)

Changing state

A substance must absorb heat energy so that it can melt or boil. The temperature of the substance does not change during melting, boiling or freezing, even though energy is still being transferred.

A heating curve is a graph showing the temperature of a substance plotted against the amount of energy it has absorbed. You may also see a cooling curve, which is obtained when a substance cools down and changes state.

The temperature stays the same during a change of state, melting or boiling, even though heat energy is still being absorbed.

The temperature also stays the same while a liquid freezes, even though heat energy is still being released to the surroundings.