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Rates of Reaction

How much Energy is Released from Burning a Fuel?

The amount of energy given out by burning a fuel
in a calorimeter can be calculated using the equation

Q = m x c x ΔT

Where Q is the energy (heat) transferred (in joules)

m is the mass of water used in the calorimeter (in grams)

c is the specific heat capacity of water (= 4·2 J / g °C)

ΔT (pronounced 'delta T') is the change in temperature (in °C).

We can know the mass of fuel burnt by weighing the burner
before and after the experiment. The change in temperature
is read from the thermometer inside the calorimeter.
To keep the calculation simple, 100 cm3 of water weighs 100 g.

Question.
How much energy is released if 0·83 gram of a fuel causes
the temperature of 100 cm3 of water to increase by 20 °C?

To find the amount of heat transferred, use the equation

Q = m x c x ΔT

= 100 x 4·2 x 20

= 8400 J.

To get our answer in joules per gram of fuel, we use the equation

energy per gram = energy released ÷ mass of fuel burnt

= 8400 ÷ 0·83

= 10120 J / g.

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