Question

Calculate the amount of energy in kilojoules needed to change 225 g of water ice at −10 ∘C to steam at 125 ∘C. The following constants may be useful: Cm (ice)=36.57 J/(mol⋅∘C) Cm (water)=75.40 J/(mol⋅∘C) Cm (steam)=36.04 J/(mol⋅∘C) ΔHfus=+6.01 kJ/mol ΔHvap=+40.67 kJ/mol Express your answer with the appropriate units.

Answer 1

We need to calculate the specific heat to each state of water and do a summation with the total.

`Q = q_1 + q_2 + q_3 + q_4 + q_5`

`Q = mC_(ice)\Delta T + m\Delta H_(fus) + mC_(water)\Delta T + m\DeltaH_(fus) + mC_(vap)\Delta T`

We have all this constant.

Now we calculate the moles in the grams given, that is

`Moles = 225 / 18 = 12.5`

`Q = (12.5*36.57*10) + (12.5*6.01*1000) + (12.5*75.40*100) + (12.5*40.67*1000) + (12.5*6.04*25)`

`Q = 4936.95 + 81135 + 101790 + 549045 + 12163.5`

`Q = 749070.45 J`

`Q = 749 KJ`