The latent heat of vapourisation of H2O at body temperature (37°C) is 2.42x106 J Kg-1. To cool the body of a 75 Kg jogger (average specific heat capacity = 3500 J Kg-1C°-1) by 1.5 °C, how many Kilograms of water in the form of sweat have to be evaporated? Q = mcΔT I'm confused about what to do with the information regarding latent heat. Is it saying that this is how much energy you need to put into one kilogram of water before it will begin evaporating? and if it is, would I just add this value (per kilogram) onto the amount of energy require to raise x kilograms of water to 100°C? I'd be really grateful if anyone can clear up any misunderstandings I have about what Latent heat is and how I would use it to solve a problem. I'd appreciate it if you left the actual question I quoted un-solved. Thanks!