SPECIFIC HEAT CAPACITY NOADSWOOD SCIENCE, 2011

SPECIFIC HEAT CAPACITY To understand and be able to calculate specific heat capacity Thursday, June 12, 2014

ENERGY EFFICIENCY Modern day homes – energy saving…

ENERGY MEASUREMENTS It is easy to measure how hot something is by using a thermometer, however it is much more difficult to measure how much heat energy is contained within something It is possible to measure how much energy is put into something…

ENERGY MEASUREMENTS Specific heat capacity can be worked out by the following: - The amount of energy it takes to heat up 1kg of the substance by 1 o C is the specific heat capacity *A calorie is the amount of energy it takes to heat 1g of water by 1 o C (about 4.2 joules)

ENERGY TESTING How could you test two liquids to find out which had the higher heat (thermal) capacity using specific heat capacity? A 50W heater can be placed into the two liquids – this heater transfers 50W of energy (50 joules per second) The more energy the liquid needs to heat it up, the higher its specific heat capacity (the amount of energy it takes to heat up 1kg of the substance by 1 o C is the specific heat capacity)

EXPERIMENT Complete the experiment to find out which of the liquids (water and salt water) has the highest specific heat capacity WaterSalt Water Thermometer 50W Heater Consider what variables will need to be controlled to ensure the experiment is accurate Which has the highest thermal capacity – explain why…

EXPERIMENT Normal water has a higher specific heat capacity than salt water – water does in fact have one of the highest specific heat capacities of any liquid… Salt (sodium chloride) has a lower specific heat capacity than water, so having this impurity in the water reduces the overall capacity of the 1kg of liquid, hence reducing the specific heat capacity (remember, both liquids still have an overall mass of 1kg (we have not added salt as an extra to the initial 1kg of water)) Specific heat capacity is affected by both the mass of the substances and its composition or structure (bonding) of the substance

SOLIDS How could you test the specific heat capacity of metals such as aluminium or copper (or for that matter anything solid)? The principal would remain the same – however rather than using 1kg of liquid and you would use 1kg of the solid (and have pre-cut holes for the thermometer and heater)…

SPECIFIC HEAT CAPACITY The energy needed to heat something can be worked out using the following equation: - Energy (J) = Mass (Kg) x Specific Heat Capacity (c) x Change In Temperature ( o C) Q = mcΔT Which of the following would require the most energy to heat? Heating 10kg of aluminium to increase its temperature by 4 o C Heating 5.8kg of copper to change its temperature from 15 o C to 25 o C Heating 5kg of water to change its temperature from 6 o C to 10 o C Example specific heat capacities: water = 4.18, aluminium = 0.9, copper = 0.39, lead = 0.13, and ethanol = 2.44

SPECIFIC HEAT CAPACITY Energy (J) = Mass (Kg) x Specific Heat Capacity (c) x Change In Temperature ( o C) Q = mcΔT Heating 10kg of aluminium to increase its temperature by 4 o C Energy = 10 x 0.9 x 4 Energy = 36 joules Heating 5.8kg of copper to increase its temperature by 10 o C Energy = 5.8 x 0.39 x 10 Energy = joules Heating 5kg of water to increase its temperature by 4 o C Energy = 5 x 4.18 x 4 Energy = 83.6 joules

STORAGE HEATERS & RADIATORS Radiators use water to heat a house – water has a very high specific heat capacity (4.18 J/Kg o C) allowing it to heat up quickly (but also lose its heat quickly) Storage heaters are made of concrete which has a much lower specific heat capacity (0.18 J/Kg o C) meaning they take a long time to heat up, but release their energy slowly over a long period of time

SUMMARY Some materials heat up quicker than others The amount of energy it takes to heat up 1kg of a substance by 1 o C is called the specific heat capacity Water has a very high specific heat capacity whilst concrete has a much lower specific heat capacity Energy = mass x specific heat capacity x change in temperature Q = mcΔT

OCEANS & SPECIFIC HEAT Earths oceans play an important role in temperature regulation of the Earth…