 So let's do a specific worked example. Let's say we had water at room temperature, say 20 degrees centigrade. And we want to put it in a frying pan. And we want to boil it dry. So it's all turned into steam. How much energy will it require? Well, first of all, you've got water at 20 degrees C. And you're going to need to increase it to 100 degrees C. Now that's specific heat capacity. So the energy you need to do that is equal to the normal equation of the specific heat capacity, which is the mass times the specific heat capacity times the change in temperature. Which in this case, specific heat capacity of water is 4186 joules per kilogram per Kelvin. Let's say we have 2 kilograms of water. That would be a nice big saucepan. This is 2. Change in temperature, going from 20 to 100. So that'll be 80 Kelvin, change in temperature. But then once it's got to water at 100 degrees, you have to turn it into steam at 100 degrees. And that's going to need the latent heat. So we now need to add the mass times the latent heat, which is this 226500 joules per kilogram. So this equals the mass, 2 kilograms times the latent heat, a specific heat capacity, 4186, times the change in temperature, plus the mass, 2 kilograms, times the latent heat of vaporization, 226500, which comes out as a whopping 5199760 joules. So about 5 megajoules. So that's why it takes so long to boil a kettle. It takes to boil it dry, a lot of energy is required.