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Year 10
OCR
Foundation

Specific latent heat (E = m l)

I can make calculations using the equation E = m × l

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New
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Year 10
OCR
Foundation

Specific latent heat (E = m l)

I can make calculations using the equation E = m × l

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Share activities with pupils
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Lesson details

Key learning points

  1. Energy transferred to a solid at its melting point allows its particles to move further apart.
  2. Energy transferred to a liquid at its boiling point allows its particles to move fast enough to get even further apart.
  3. The energy transferred to melt a solid at its melting point is proportional to the mass of the solid.
  4. The energy transferred to melt 1 kg of a solid at its melting point is proportional to the solid’s specific latent heat.
  5. The energy transferred to boil 1 kg of a liquid at its boiling point is proportional to it’s specific latent heat.

Keywords

  • Melting - the change of state from a solid to a liquid; happens at a fixed temperature for pure substances

  • Boiling - the change of state from a liquid to a gas; happens at a fixed temperature for pure substances

  • Specific latent heat - the change in energy when 1 kg of a substance changes state

  • Specific heat capacity - the change in internal energy when the temperature of 1 kg of a substance changes by 1°C

Common misconception

The temperature of ice is always 0ºC and the temperature of water in the liquid state cannot be 0°C.

Make explicit observations that water can be in either or both of the solid and liquid states at 0°C.

Provide pupils with examples of exam questions to practise so that they become familiar with thinking about specific latent heat in a range of different contexts.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of the following words is used to describe the change of state from a gas to a liquid?
evaporation
boiling
freezing
melting
Correct answer: condensing
Q2.
Which of the following changes of state result in an increase in internal energy?
freezing
Correct answer: melting
Correct answer: boiling
condensing
none of these
Q3.
In which state of matter are the electrostatic forces between particles the strongest?
Correct answer: solid
liquid
gas
they are all equal
there are no forces in any state
Q4.
A substance is heated continuously from its solid state until it is in its gas state. Sort the following statements into the correct order to describe how the temperature of the substance changes.
1 - Its temperature increases until it starts to melt.
2 - Changing into the liquid state, its temperature remains constant.
3 - Its temperature increases until it starts to boil.
4 - The temperature of the substance is constant as it changes into its gas state.
5 - Its temperature continues to increase.
Q5.
A 100 g sample of pure silver has a melting point of 962°C. What is the melting point of a 50 g sample of the same material?
481°C
Correct answer: 962°C
1924°C
It is not possible to know.
Q6.
Calculate the energy needed to heat 8.0 kg of vegetable oil from 20°C to 170°C if the specific heat capacity of the oil is 2000 J/kg/°C.
2 400 J
2.4 kJ
320 kJ
Correct answer: 2.4 MJ
2.72 MJ

Exit quiz

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6 Questions

Q1.
Match the following key words or phrases to their definition.
Correct Answer:melting,the change from a solid state to a liquid state

the change from a solid state to a liquid state

Correct Answer:boiling,the change from a liquid state to a gas state

the change from a liquid state to a gas state

Correct Answer:specific latent heat,the energy transferred when 1 kg of a substance changes state

the energy transferred when 1 kg of a substance changes state

Correct Answer:specific heat capacity,the change in internal energy when temperature of 1 kg changes by 1°C

the change in internal energy when temperature of 1 kg changes by 1°C

Q2.
Which of the following statements about changes of state for a pure substance at constant pressure are correct?
Correct answer: Boiling happens at a specific temperature.
Boiling happens over a range of temperatures.
Freezing and melting happen at different temperatures.
Correct answer: Boiling and condensing happen at the same temperature.
Boiling and melting happen at the same temperature.
Q3.
Why does the temperature stay constant when a substance is boiling as it is heated?
The average speed of the particles is decreasing.
The fastest particles slow down when they escape.
Correct answer: The fastest particles escape, keeping the average speed the same.
The particles are gaining mass, so their speed stays the same.
The forces between the particles are increasing.
Q4.
Which of the following equations, to calculate the energy required to change state, is correct?
energy = mass × specific heat capacity × temperature change (E = m c Δθ)
energy = mass × specific heat capacity × temperature (E = m c θ)
energy = mass ÷ specific latent heat (E = m ÷ l)
Correct answer: energy = mass × specific latent heat (E = m l)
Q5.
The specific latent heat of fusion for ice (melting) is 334 kJ/kg. Calculate the energy required to melt 600 g of ice. Give your answer in kJ to 2 significant figures.
Correct Answer: 200, 200 kJ, 200 kilojoules
Q6.
The specific latent heat of ice is 334 kJ/kg and its specific heat capacity is 2.11 kJ/kg/°C. Calculate the energy required to fully melt a 2.0 kg block of ice which starts at a temperature of –20°C.
84.4 kJ
376.2 kJ
583.6 kJ
668 kJ
Correct answer: 752.4 kJ