If two objects have different temperatures, in which direction will heat move? For how long?

Atoms in molecules and solids are held together by chemical bonds. Chemical bonds are electromagnetic in origin, but can be modeled well by tiny springs. Two atoms held together by a spring have an equilibrium position. If they are pushed closer together, they repel each other. If they are pulled farther apart, they attract each other. If they are displaced in any way from their equilibrium position and then released, they start vibrating about their equilibrium position. An atom can form different chemical bonds with a variety of other atoms. Different bonds are represented by springs with different spring constants. The stiffer the spring, the more work it takes to pull the atoms apart. If enough work is done, then the spring is stretched too much and it breaks, i.e. the chemical bond breaks