1.3 Some numbers

We hope you enjoyed doing Activity 1 and managed to get your water up to boiling point. Now, let’s do the calculation.

First, you need to know the mass of water in kilograms on your spoon. A normal tablespoon holds about 15 millilitres of water. Since 1 millilitre of water has a mass of about 1 gram, that’s about 15 grams. You need to divide the mass of water in grams by 1000 to get the mass of water in kg.

Now, you need to estimate the temperature of the water when you started. In the UK, water that comes straight from the tap is usually about 10 °C, but this will, of course, vary according to your circumstances. Water boils at 100 °C, so by subtraction, you can work out the temperature rise in °C. As you found in How do we find out the energy in food?, you can calculate the energy in kilocalories (kcal) by multiplying the rise in temperature by the mass of water in kg.

So, how many kilocalories did your peanut contain?