Saturday, 6 September 2014

Specific heat and latent heat problems


            Specific heat and latent heat problems

Heat energy = mcΔθ Latent heat energy = mL

Specific heat capacities:- water 4200 Jkg-1K-1   copper 385 Jkg-1K-1 
Specific latent heats of water:- fusion 3.3x105 Jkg-1    vaporisation 2.25x106 Jkg-1 

1. (a) A copper saucepan of mass 250g is filled with 850g of water at 18°C. A 500W heater is then placed in the water and switched on for 5 minutes. What is the theoretical temperature of the water after this time?
(b) Why will the actual rise be less than this? 

2. How much heat is needed to heat 250g of water at 15°C to steam at 100°C? 

3. A hot copper rivet of mass 150g is dropped into 250g of water initially at 16°C. If the water temperature rises to 35°C what was the initial temperature of the rivet? 

4. How does the high value of the specific heat capacity of water help to reduce the variation in temperature of land masses adjacent to oceans? 

5. A thin copper wire fixed to two 1 kg copper masses hangs over a block of ice. Due to the pressure increase some of the ice melts and the wire cuts into the block, the water re-freezing above the wire. If 20g of ice is melted in this way estimate the rise in temperature of the two 1 kg masses.