Topic Menu

Cyber-chess a chess instruction site

Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q11. The diagram shows a bunsen burner heating some water in a beaker.

Eventually the water changes into steam.

(a) Explain how the internal energy of the water changes as it is heated from 20 °C to 25 °C

The mean kinetic energy of the particles in the water (the water molecules) increases as the water absorbs the heat energy, this increases the internal energy of the water.

Just saying 'kinetic energy increases' was considered insufficient by itself to get you a mark. Use complete sentences and explain what happens as fully as you can. You had to specify it was water molecules that have their kinetic energy increased.

Talking about 'particles vibrating' gave you no marks - the translational kinetic energy of the particles increases.

[2 marks]

(b) Choose one of the sentences below to explain how is the particle model can be used to explain the difference in density between a liquid and a gas.

Tick your choice.

Particles in a gas have less kinetic energy than particles in a liquid.  
Particles in a gas have more potential energy than particles in a liquid.
Particles in a liquid are further apart than particles in a gas.  
Particles in a liquid are larger than particles in a gas.  

[1 mark]

(c) Brad measured the mass of boiling water that was turned into steam in five minutes.

Explain how the he could use this information to estimate the power output of the bunsen burner in watts.

Energy given to water E = mL

where

E = the energy transferred in joules,

m = the mass of the water changing state in kilograms

and L = the latent heat of vapourisation of water in J/kg

You needed to give the equation AND define what the letters stand for to get the mark.

The power output of the bunsen burner (W) = energy transferred to the water (J)/ time of transfer (s)

P = E/t

P = m L/t

As the time interval is 5 minutes t = 60 x 5 = 300s

Therefore

P = m L/300

[4 marks]

(7 marks total)