SPECIFI

C HEAT

CAPA

CITY

NOADSWOOD SCIENCE, 2011

SPECIFIC HEAT CAPACITY

To understand and be able to calculate specific heat capacity

Tuesday, April 11, 2023

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 1oC is the specific heat capacity

• *A calorie is the amount of energy it takes to heat 1g of water by 1oC (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 1oC 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

Water Salt Water

Thermometer

Thermometer

50W Heater

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 (oC)

Q = mcΔT

• Which of the following would require the most energy to heat?• Heating 10kg of aluminium to increase its temperature by

4oC• Heating 5.8kg of copper to change its temperature from

15oC to 25oC • Heating 5kg of water to change its temperature from 6oC to

10oC • 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 (oC)

Q = mcΔT

• Heating 10kg of aluminium to increase its temperature by 4oC

Energy = 10 x 0.9 x 4

Energy = 36 joules

• Heating 5.8kg of copper to increase its temperature by 10oC

Energy = 5.8 x 0.39 x 10

Energy = 22.62 joules

• Heating 5kg of water to increase its temperature by 4oC

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/KgoC) 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/KgoC) 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 1oC 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

• Earth’s oceans play an important role in temperature regulation of the Earth…