How many grams of fuel?

Question

A backpacker wants to carry enough fuel to heat 2.50 kg of water from 25.0 °C to 100.0 °C. If the fuel

he carries produces 36 kJ of heat per gram when it burns, how much fuel should he carry? (For the sake

of simplicity, assume that the transfer of heat is 100% efficient.)

Answer 1

To determine how much heat is needed used the following equation:

q(heat) = m(mass) x C(specific heat) x ΔT

q = 2.5 g x 4.186 J/ kg x °C x (100 - 25 )

q = 784.9 kJ

Now we will use dimensional analysis:

784.9 kJ x 1 gram/ 36 kJ = 21.8 grams

In a real-world scenario, this would be rounded up to 22 grams.