Student calculation sheet P6.
5
Name ..................................................................... Class .................. Date .....................
Latent heat
Specification references:
P3.2.3 Changes of heat and specific latent heat
M1a, M3b, M3c, M3d, M4a
Aims
In this worksheet, you will work through two worked examples designed to allow
you to improve your maths skills. The focus is on solving algebraic equations,
by substituting numbers into the equation and rearranging if needed.
Learning outcomes
After completing this activity you should be able to:
identify when to use latent heat of fusion and latent heat of vaporisation
apply the equation for latent heat
substitute numerical values into algebraic equations using appropriate
units
solve algebraic equations.
Setting the scene
In this worksheet, you will be using the following equation:
Thermal energy for a change in state (J) mass (kg) specific latent heat (J/kg)
Useful values:
Latent heat of vaporisation
Substance Latent heat of fusion (J/kg)
(J/kg)
water 334 000 2 260 000
oxygen 14 000 210 000
silver 88 000 2 300 000
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 1
Student calculation sheet P6.5
Name ..................................................................... Class .................. Date .....................
Worked examples
1 Calculate the energy released when 100 g of steam condenses.
Step 1: Identify what you know and convert to standard units
Mass 100 g 0.1 kg
Since it is a change of state between gas and liquid you will need to use the
latent heat of vaporisation.
Latent heat of vaporisation 2 260 000 J/Kg
Step 2: Substitute the numbers into the equation
Energy required mass specific latent heat of vaporisation
0.1 2 260 000
226 000 J
2 Calculate the mass of ice lost from an iceberg melting, if the energy supplied
was 835 000 000J.
Step 1: Identify what you know and convert to standard units
Energy 835 000 000J
Since it is a change of state between a solid and a liquid, you will need to use
the latent heat of fusion.
Latent heat of fusion 334 000 J/Kg
Step 2: Substitute the numbers into the equation
Energy required mass specific latent heat
835 000 000 J mass 334 000
Step 3 Rearrange the equation to make mass the subject of the equation.
Divide both sides of the equation by 334 000
2500 kg mass
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 2
Student calculation sheet P6.5
Name ..................................................................... Class .................. Date .....................
Latent heat of vaporisation
Substance Latent heat of fusion (J/kg)
(J/kg)
water 334 000 2 260 000
oxygen 14 000 210 000
silver 88 000 2 300 000
Questions
1 Before freezers and fridges, people used to buy ice to keep their food cool. The
very rich even filled a special building called an icehouse to make sure they had
ice throughout the summer. Calculate how much energy is required to melt
a a 10 kg block of ice,
(2)
b a 1000 kg block of ice.
(2)
2 A jeweller melts 500 g of silver to pour into a mould. Calculate how much
energy was released as the silver solidified.
(2)
3 A container has 200 g of liquid oxygen in it. Calculate how much energy will be
required to evaporate all the oxygen, assuming it is at its boiling point.
(2)
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This resource sheet may have been changed from the original. 3
Student calculation sheet P6.5
Name ..................................................................... Class .................. Date .....................
4 A kettle fails to switch off and boils for 5 minutes, wasting 600 000 J of energy.
Calculate the mass of water lost during this time.
(3)
5) A student takes measurements to determine the latent heat of vaporisation of
ethanol. They discover it takes 8460 J to evaporate 10 g from boiling point.
Calculate the latent heat of vaporisation of ethanol.
(3)
6) Calculate the mass of water you could evaporate from its boiling point with the energy required to
melt 800 g of silver from its melting point.
(5)
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 4
