Physics 2 starts with a gas: trillions of atoms colliding at random, yet described by a few numbers (pressure, volume, temperature). This unit connects those numbers to atomic motion, then follows energy as it moves by heating and by work (the first law) and as it spreads out (the second law).
Gas pressure comes from atoms colliding with surfaces; temperature measures the atoms' average kinetic energy. An ideal gas (random motion, tiny atoms, elastic collisions, no other forces) obeys PV = nRT = Nk_BT, and a P–T graph extrapolates to zero pressure at absolute zero.
Systems in thermal contact exchange energy by conduction, convection and radiation, spontaneously from higher to lower temperature, until they reach thermal equilibrium: the same temperature and no net energy transfer.
An ideal monatomic gas's internal energy is the atoms' kinetic energy, U = (3/2)nRT. The first law, ΔU = Q + W, accounts for energy added by heating (Q) and work done on the gas (W = −PΔV). On a PV diagram, |W| is the area under the path; special processes are isobaric, isovolumetric, isothermal and adiabatic.
Q = mcΔT gives the energy to change a material's temperature, with specific heat c a property of the material. Conduction rate Q/Δt = kAΔT/L depends on the material's conductivity k, its area and thickness, and the temperature difference.
Entropy describes how spread out energy is and how much is unavailable to do work. The total entropy of an isolated system never decreases, and isolated systems move toward equilibrium, where entropy is maximum. A closed system's entropy can decrease if energy leaves it. Qualitative only.