 Heat travels from hot to cold  The bigger the temperature difference the faster the rate of transfer

 The internal energy (sometimes called the random thermal energy) of a substance is the sum of  the kinetic energy and  the potential energy of its particles.

 Potential energy is due to the interaction of neighbouring particles.  This is therefore very significant in solids and liquids but less so in gases.  In fact ideal gases have NO potential energy – just kinetic!

 Kinetic energy is due to the movement of the particles in the substance.  The faster they move  the higher the KE and  the higher the temperature

 When you give heat energy to a substance it gets hotter if the heat is used to increase the KE of the particles.  How much hotter depends on two things:  Its mass and  What it is made of

 It makes sense that  the more of it you have the more energy you would have to give it to raise the temperature a certain amount of a substance and that  different materials would need different amounts of heat to get hotter as their structure and the number of particles in a certain mass is different for each type.  Values are therefore quoted for the heat needed to raise the temperature of 1kg of a substance by 1K

 Q = mc  m = mass (kg) c = specific heat capacity (J kg -1 K -1 ) Q = heat energy (J)  = temperature (K) The  means ‘difference in’ because if you put heat in you get an increase – if heat comes out of the system the temperature goes down. You can therefore use signs to indicate gain or loss.

 The Specific Heat Capacity (c) of a substance is the quantity of energy required to raise the temperature of 1kg of the substance by 1K.

 The biggest changes in temperature of a given mass of a substance will occur in those that have low specific heat capacities - because it doesn't take much energy for them to get hotter!

 Water has a very large SHC  4200 J kg -1 K -1  This is about ten times that of a metal.

 It makes an excellent heat store.  To store heat you want the thing it is stored in not to get too hot – otherwise it will lose heat very quickly to the surroundings – remember heat loss to the surroundings depends on the diference in temperature between the object and its surroundings (  T)

 Water has a large SHC  Therefore is makes an excellent coolant.  A good coolant will take a lot of heat away from whatever you are trying to cool without getting too hot itself.  Once the coolant is the same temperature as the thing you want cooling it will stop taking heat from it!

 A kettle of power 2kW holds 2 litres of water at room temperature – 20 o C.  If the kettle is left on for 5 minutes will it boil?  C water = 4200 J kg -1 K -1

 Where does the energy given to the water come from?  The electricity supply via the kettle’s electrical element  How much energy is given to the water?  2000 J every second for 5 minutes  Calculate this!  2000 x 5 x 60 = 6 x 10 5 J

 Energy input = 6 x 10 5 J  How much energy is required to bring the water to boiling point?  What equation do we need?  Q = mc   Okay, so how much energy is needed?  (Remember that 1 litre of water has a mass of 1kg and the SHC of water is 4200 J kg -1 K -1 )  Q = 2 X 4200 X 80 = 6.72 x 10 5 J

 Energy input = 6 x 10 5 J  Energy required to boil the water = 6.72 x 10 5 J  What does this mean?  The water wouldn’t even boil

Molecular masses and SHC Remembering the work done on ideal gas laws, we should realise there is a link between the temperature and the number of moles of a substance ie the number of particles. They are inversely proportional as shown ……… PV = nRT pressure, volume and mass of gas If pressure, volume and mass of gas are constant then ……… T  1/n

Therefore if the number of particles making up a mass decreases the temperature would be higher for the same energy input!! In other words more dense atoms (taking less atoms to make up a kilogram) will be at a higher temperature for the same energy input. dense substances have a lower specific heat capacity than less dense ones. Therefore dense substances have a lower specific heat capacity than less dense ones. Copper380 Jkg -1 K -1 E.g. Copper has a SHC of 380 Jkg -1 K -1 whereas Aluminium880 Jkg -1 K -1 Aluminium has a SHC of 880 Jkg -1 K -1 Since the temperature is linked to the energy of a molecule or atom if the same energy is pumped into less atoms their average energy must be higher and therefore their temperature!

Storage Heaters These are the most commonly seen electrical device relying on specific heat capacity. Cheap overnight electricity is used to heat concrete blocks. In the day they are allowed to cool by regulating the air flow over them by vents being adjusted. This regulates the rate of heat being delivered to the room. Downside – if they cool off too early in the day they cannot be heated again until the overnight power supply comes online. The concrete is used as it has a fairly high density, therefore only a moderate SHC, but can easily be heated to high temperatures safely and therefore store a large amount of heat energy.

You should make certain to learn the methods for this practical and pay attention to the sources of error. A major source of error is the energy supplied by the power supply not reaching the thermometer as it leaks away to the surroundings or being “used” to heat the heater & thermometer. In metal blocks there will be a distribution of temperatures throughout the block depending on the position relative to the heater With heating liquids the temperature can easily be made consistent by regular stirring Determining SHC and the sources of error

Minimising errors The block/calorimeter needs to be well insulated to reduce heat loss to the surroundings Use “small” thermometers whose mass is small compared to that of the block/liquid so that they use as little energy as possible to get them to the temperature of the sample after Allow the thermometer to reach a maximum value after turning the power supply off in order to record the temperature rise caused by all the energy supplied to the heater.