Thursday, 4 September 2014

Change of state and Latent heat Questions

Change of state and Latent heat      

1.  What happens to the molecules when a liquid changes to a gas?

2.  What happens to the molecules in a solid when it is cooled?

    3.    What temperature changes occur when water changes to ice at 0oC?

    4.    What happens to the molecules of a liquid when it is evaporating?

    5.    What is meant by
(a) specific latent heat of fusion?
(b) specific latent heat of vaporisation?

   6.    Why does your hand feel cold if you put a drop of methylated spirit on it?

   7.    How does sweating help to keep you cool?

   8.    You can buy aerosol freezers for cooling transistors etc. Explain whether you think that the molecules of the liquid evaporate easily.

   9.    How much energy is needed to turn 3 kg of water, at 1000C into steam at 1000C? Specific latent heat of vaporisation of water = 2 300 000 J/kg.

  10.  Why is a scald by steam at 1000C much more painful than one by water at 1000C?

11. How much heat energy is needed to melt 500 g of ice (Specific latent heat of fusion of ice = 335 000 J/kg)

12. How long will it take a 100 W heater to melt 2 kg of ice at 00C?

13. Why is energy needed to melt a solid? (mention atoms or molecules in your answer)