This is the question:

"How much heat is required to turn 1.5 kg of water ice at a temperature of −25°C into 1.5 kg of water vapour at 150°C? (to 2 s.f and in MJ)

[cice = 2090 J kg−1 K−1, cwater = 4190 J kg−1 K−1, cwater-vapour = 2010 J kg−1 K−1, Lvap-water = 2256×103 J kg−1, Lfus-water = 333×103 J kg−1]"

So I used Q=mL twice - one for vap-water and one for fus-water.

I used Q=mc/_\T three times, each for each variation of specific heat capacity (c).

I kept the change in temperature constant - from -25C to 150C, so a change of 175 degrees celsius total.

I used Q1+Q2+Q3... for the last step and so added the results of all of these together which came to 6059625J, which to MJ is 6.1MJ.

It's definitely within the MJ range, so I thought it'd be right but it's not.

I wonder where I went wrong here,

any idea?

-I