thermal properties of matter (i need help)

Question

1.) A beaker containing 0.250kg of water at 10°c has a 2.0kw heater immersed in it. Find the time needed to rurn the water completely to steam.

2) what is the amount of energy released when 5g of steam at 100°c changes to water at 80°c? (Specific latent heat of vaporisation of steam = 2300 j/g; specific heat of water = 4.2J/(g.°C) )

3) what is the amount of energy required to change 10g of ice at 0°c to water at 20°c [specific heat latent heat of fusion of ice =336j/g, specific heat capacity of water = 4.2J/(g.°c)]

Answer 1

1.) 1 W = 1 J/sec thus 2.0 Kw = 2000 J/sec

heat needed to raise 250 g H2O from 10º to 100º = (250g)(4.184 J/g)(90º) = 94,140 J

heat needed to convert 250 g H2O to steam at 100º = (250 g)(2300 J/g) = 575,000 J

Total energy needed = 575,000 + 94.140 = 669,140 J

Time needed = 669,140 J x 1 sec/2000 J = 334.57 sec = 5.58 minutes = 5 minutes 35 seconds

 

(2) Use q = mC∆T and q = mC to answer this and #3 remembering there is not ∆T when there is a phase change (i.e. going from solid to liquid or liquid to gas)