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Lesson 3 of 8

Mixing substances of different temperatures

I can predict the resulting temperature when two substances of different temperatures are put together.

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Lesson 3 of 8
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Mixing substances of different temperatures

I can predict the resulting temperature when two substances of different temperatures are put together.

Lesson details

Key learning points

  1. Mixing hot water with cold water results in water cooler than the hot water and warmer than the cold.
  2. When hot and cold water are mixed, the temperature is closer to that of the water there was more of.
  3. A cold object placed in hot water makes the water particles move more slowly and those in the object move more quickly.
  4. A hot object placed in cold water makes the water particles move more quickly and those in the object move more slowly.

Keywords

  • Volume - the amount of space an object takes up

  • Particle model - the idea that all objects are made of tiny particles that are in constant motion

  • Temperature - the higher the temperature of an object, the faster its particles move and the hotter it is

  • Collide - when two objects bump into each other

Common misconception

When samples of water are added at different temperatures, some pupils add or subtract the temperatures, applying a mathematical process without appearing to think about what is happening.

Ask pupils to predict changes to the resulting temperature using water at a range of starting temperatures and then demonstrate each one, measuring the temperature of the resultant mixture each time.

Marbles shaken in a tray can be useful model for a liquid, but their (relative) spacing must be made greater than it would be in a liquid to give the marbles space to move and collide. Emphasise the fact that particles in a real liquid are much closer together.
Teacher tip

Equipment

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2026), 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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Prior knowledge starter quiz

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6 Questions

Q1.
A rectangular block of steel has a length of 8 cm, a width of 4 cm and a height of 3 cm. What is the volume of the block in cm³?

Correct Answer: 96, 96 cm³, 96 centimetres cubed

Q2.
Which of the following pieces of equipment can measure the volume of a liquid most precisely?

beaker
conical flask
Correct answer: measuring cylinder
test tube

Q3.
In which state of matter do the particles in water move the fastest?

solid
liquid
Correct answer: gas

Q4.
How close together are the particles of a liquid?

Correct answer: touching each other
close together with a few touching
close together with spaces between each one
spread out with large gaps between

Q5.
What happens to the particles that make up a gas when it is heated to a higher temperature?

They move at the same speed.
They move at the same speed and spread further apart.
They move more quickly.
Correct answer: They move more quickly and spread further apart.

Q6.
Why would touching a very hot piece of solid metal burn your skin?

Correct answer: Its particles transfer energy to your skin so quickly they damage skin cells.
Its particles are moving around so quickly they damage skin cells.
Its particles are spreading out so quickly they damage skin cells.

Assessment exit quiz

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6 Questions

Q1.
50 cm³ of water at 80°C is mixed with 50 cm³ of water at 40°C. What will be the resulting temperature of the mixture?

40°C
Correct answer: 60°C
80°C
It is impossible to predict.

Q2.
100 cm³ of water at 60°C is mixed with 50 cm³ of water at 30°C. What will be the resulting temperature of the mixture?

30°C
40°C
Correct answer: 50°C
60°C

Q3.
100 cm³ of water at 80°C is mixed with 300 cm³ of water at 40°C. What will be the resulting temperature of the mixture?

80°C
70°C
60°C
Correct answer: 50°C
40°C

Q4.
What word describes the directions in which particles of water move in the liquid or gas state?

Correct Answer: random, haphazard

Q5.
What happens when faster moving particles of a hot solid collide with slower moving particles of a cold liquid?

Correct answer: On average, the particles of the solid slow down.
On average, the particles of the solid speed up.
On average, the particles of the liquid slow down.
Correct answer: On average, the particles of the liquid speed up.

Q6.
Why does a cube of solid water (ice) melt when it is put into a glass of lemonade at room temperature?

Particles of the lemonade cause particles of the water to break apart.
Particles of the lemonade cause particles of the water to melt.
Correct answer: Particles of the lemonade cause particles of the water to move faster.
Particles of the lemonade cause particles of the water to shrink.

Lesson appears in

UnitScience / Heating and cooling

Science

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