Heat is a bit like time – it only flows in one direction. From heat’s point of view it flows from hot to cold.
Here is a dead simple experiment to show this – and it contains some good IB Chemistry as well.
Get an ice cube. Soak a piece of string in water. Lay the end of the string on the ice cube and sprinkle some salt onto the string. The string will freeze onto the ice cube. But why? Well, the salt melts the ice – this needs heat energy and it takes this from the string – cooling it enough to freeze it!