The heat of combustion of octane, C 8 H 18 , can be measured in a way similar to

Question

The heat of combustion of octane, C8H18, can be measured in a way similar to the method you used to measure the heat of neutralization. The bomb calorimeter is used instead of a coffee cup.

The reaction is: 2C8H18 (l)+ 25O2 (g) ----> 16 CO2 (g)+ 18 H2O (l)

When 1.02g of octane was burned in a bomb calorimeter, the temperature of 1.00kg of water was raised from 22.0°C to 35.3°C. The specific heat of water is 4.184J/(g °C ). How many moles of octane were burned? What is the heat combustion (H) of octane in kilojoules per mole?

Explanation / Answer

The specific heat of water = 4.184 J / g C

The amount of octane burnt = 1.02 g

Molecular weight of octane = 114 g / mole

a) So moles of octane = mass / mol wt = 1.02 / 114 = 0.00894 moles

b) The heat evolved by burning will be consumed by water in heating

So Q = heat evolved = mass of water x specific heat of water x change in temperature

Q = 1000 g x 4.184 X (35.3-22) = 55647.2 Joules

This heat will be evolved due to burning of 0.00894 moles

So heat of comubstion of octane per mole = 55647.2 Joules / 0.00894 moles = 6224 KJ moles

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