Heat flow occurs from a hotter substance to a cooler substance. For example, a metal at 400°C is placed into water of temperature 60°C. The heat will flow from 400°C-60°C.
The greater the temperature difference between hot and cold, the greater rate of heat flow.
The First Law Of Thermodynamics
Change in internal energy (J) = work done on the substance (J) + heat supplied to the system (J)
The 'Zeroth' Law Of ThermodynamicsIf body A is in thermal equilibrium with body B and body B is in thermal equilibrium with body C, then bodies A and C are also in thermal equilibrium.
These bodies have a common property called temperature.