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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 cm^{3}
of water weighs 100 g.

Question.

How much energy is released if 0·83
gram of a fuel causes

the temperature of 100 cm^{3}
of water to increase
by 20 °C?

Answer.

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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