Heating and cooling

Target

To know the difference between heat and temperature and to know more about the

Celsius temperature scale.

Monday 10 April 2023

It takes 2 minutes to heat the water in the kettle to 100oC.

It takes 2 hours to heat the water in the hot water tank to 60oC.

The tanks needs far more HEAT energy than the kettle because there is so much more water.

Heat and temperature

• Heat and temperature are not the same thing.

• Heat is a form of energy it is measured in Joules.

• Temperature is a measure of the level of heat. It is measured in degrees Celsius. (oC)

Heat and temperature

In this experiment the coin is very hot (about 800oC) but it has very little heat. When the coin is submerged in the cold water the heat is taken up in the water. There is so little heat transferred the temperature of the water rises less than 1oC.

The Celsius scale

• The temperature scale in Celsius was created by taking frozen ice to be 0oC and boiling water to be 100oC.

• This picture shows the world’s largest thermometer.

The freezing point of water

A temperature of 0oC is the temperature at which water freezes at sea level air pressure.

However ice will freeze below 0oC if salt is added to it. As shown in the experiment where salt is added to a funnel containing ice. The temperature drops to about -14oC.

The freezing point of water

However ice can freeze below 0oC if it is subjected to high pressure as shown in the experiment where a wire caring a heavy weight is suspended over the block of ice.

The wire passes through the ice leaving a solid block behind.

The ice below the wire melts under high pressure but then freezes again once the wire passes though and the pressure drops.

The boiling point of water

The boiling point of water is 100oC at sea level pressure of air.

The boiling point rises if the air pressure rises.

In past times (before microwave ovens) people used to cook food in pressure cookers – the boiling water was above 100oC so the food cooked faster.

The boiling point of water

Water boils well below 100oC when the pressure drops as shown in the experiment where a flask of boiling water is sealed and inverted.

The pressure drops because water vapour takes up a lot of the space inside the flask, when the flask is cooled the water vapour condenses and the pressure drops.

The graph shows how low the boiling point can drop at low pressures.

The boiling point of water

Explain why the coffee is always cold on Mount Everest!

Temperature ranges

• The thermometer shown give an idea of some possible temperatures.

• Day temperatures in the UK can vary from –10oCto 35oC.

Temperature ranges

The hottest temperature ever recorded was 58oC in Libya (1922) and the coldest -89oC in Antarctica (1983).

Global warming

These photographs show how the Arctic ice cap has melted from 1979 to 2003.

1979

2003

Homework questions

Hodder B –Page 29

Questions – Core Science 1 – pages 108 and 109

• 1. Temperature rises as water is heated at first.• 2. Temperature stays the same when water is boiling.• 3. Temperature stays the same.• 4. A and B melt (in warmer surroundings) C stays frozen (in very cold

surroundings).• 5. B takes longer to melt because the air temperature is not as hot.• 6. Water mass is less after one week.• 7. Hair dryer is warm air and moving air – both help to evaporate

water.• 8. Sunny and breezy dry faster – warm moving air dries the clothes

faster.• 9. Person soaked in water feels coolest because evaporation causes

cooling.• 10. Sweating produces water on the skin which will cool the body as

it evaporates.