Finding heat of Combustion:

Find the total number of calories and heat of combustionwhen 200 g of H₂O is warmed from 20^oC to 45^oC by 0.50 g of candle. This means that Δt is 25C^o.

Total heat--

Q = mcΔt

Q = (200g)(1cal/g^.C^o)(25C^o)

Q = 5000 cal

Heat of Combustion

= Q/g of candle

= 5000 cal/0.5 g

= 10,000 cal/g

Finding Heat of Solidification:

If 200 g of H₂O is warmed by 10.0 g of wax from 20.0^oC to 22.4^oC. This means that Δt is 2.4C^o.

Total heat--

Q = mcΔt

Q = (200g)(1cal/g^.C^o)(2.4C^o)

Q = 480 cal

Ht. of Solidification

= Q/10.0 g of wax

= 480 cal/10.0g

= 48 cal/g

Compare the heats:

10000 cal/g /48 cal/g

= A ratio of 200

So the chemical change (burning) takes over 200 times the energy of the physical change (freezing)!

And a nuclear change takes over a million times the energy of a chemical change! WOW!