Question

The heat combustion of Butane ∆Ho
RXN is equal to the heat generated by the cooling of
17.2 g of water from 100Co
to 20Co (the specific heat for water is s = 4.186 J/g.C).
Calculate the mass of Butane that needs to be combusted to obtain 350 kJ of heat.

Answer 1

heat of combustion of butane = heat generated by cooling 17.2 g of water from 100 C to 20 C

so let us calcuate the heat generated by water

heat given by water = mass of water x specific heat of water x delta T

= 17.2 g x 4.186J/g.C x 80C

=5759.9 J

Combustion reaction of butane is

C4H10(g) + 13/2 O2 (g) -------------> 4CO2(g) + 5 H2O(g)

Thus 1 mole of butane (58g/mol) gives 5759.9J of heat  

to get 350kJ = 350x10³ J f heat

the mass of buutane required = 350x10³ J x 58g/mol / 5759.9J/mol

=3.524x10³ g

= 3.524 kg of butane