Question

Thermochemistry

1. How much heat is required to convert 180g of ice at -40C to steam at 120C?

2. Write the thermochemical equation for the decomposition of one mole of methanol, CH3OH(l), into its elements in their stable states at 25C and 1atm.

Answer 1

There are five steps to calculate heat

1. ice melt to 0C

2. melt of ice at 0C
3. ice converted to water

4. water converted to boil water

5. .water converted to water vapor at 120C

specific heats

ice 2.05j/g-c

water 4.184j/g-c

steam 2.08j/g-c

heat of fusion of ice = 334j/g

Heat of vaporisation =2270j/g

1. Q = mCt

     = 180*2.05*50 = 18450 J
2. heat = 180*334 =60120 joules
3. heat = mct

           = 180*4.184*100 = 75312 joules
4. heat = 180*2270

          = 408600 joules
5. heat = mct

        = 180*2.08*20 = 7488 joules
Total heat required = 18450 J + 60120 j +75312 joules + 408600 joules + 7488 joules

                           = 569970 joules = 569.970Kj

CH3OH -----> C+ 2H2+ 1/2 O2