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Heat Questions - GCSE Level

Q16. A 'can-chiller' is used to make a can of drink colder. The diagram shows a can-chiller.

(a)

The initial temperature of the liquid in the can was 25.0 °C.

The can-chiller decreased the temperature of the liquid to 20.0 °C.

The amount of energy transferred from the liquid was 6930 J.

The mass of liquid in the can was 330 g.

Calculate the specific heat capacity of the liquid in the can - ignore the heat transferred from the can itself.

Energy transferred (J) = mass (kg) x temperature change (°C) x SHC (J kg-1 °C-1)

6930 = 0.330 x 0.50 x c

c = 6930/0.165

c = 42,000 J kg-1 °C-1

[4 marks]

(b) Explain how energy is transferred through the metal walls of the can of drink by conduction.

In a metal atom there are loosely held 'free' valence electrons that gain kinetic energy and then transfer some of that energy to other electrons / ions / atoms by collisionwith them.

[4 marks]

(c) Explain howthe energy from the can of drink is transferred to the air around the can-chiller by a convection current that is set up around the can-chiller.

As they get warmer air particles become less densely packed - spread out - which causes the air in that region to become less dense. Less dense air rises within cooler denser air taking energy from the can with it.

Particles do not become less dense the arrangment of the particles becomes less dense as the particles move further apart.

Never say 'heat rises' - the warmer air rises because of density difference!

[3 marks]

(d) The can-chiller has metal cooling fins that are designed to transfer energy quickly to the surroundings.

Give two features that would help the metal cooling fins to transfer energy quickly to the surroundings.

A large surface area increases contact and transfer each second.

A black/dark dull colouration helps heat transfer by radiation.

[2 marks]

(13 marks total)