The Zeroth Law of Thermodynamics Notes: Laws of Thermodynamics The Zeroth Law of Thermodynamics If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other. Example: Two thermometers measuring the same body should give equivalent values.

First Law of Thermodynamics Increase in internal energy External work done by the system Heat added = + Whenever heat is added to a system, it transforms to an equal amount of some other form of energy. A system is any group of atoms, molecules, or objects. Example: steam engine: fuel is used to raise the temperature of water to boil, the steam can turn a wheel to make mechanical energy that can do work

Another way of saying the first law: The change in the internal energy of a substance is the sum of the heat transferred plus the work done Change in Internal Energy = Heat transferred + Work done

Internal energy “internal energy” is associated with the random motion of all of the molecules that make up an object- the more molecules there are, the more internal energy is possible. Hot beverage Massive iceberg The iceberg has more internal energy because it has more molecules.

Heat Engines A heat engine is any device that changes internal energy into mechanical work Power generation plants use fuels to make steam-driven turbines that allow production of electricity

Another example is an automobile engine which converts gasoline into motion. Much of the energy released by the combustion of fuel does not produce the mechanical energy of motion in the car. In what form does much of that released chemical potential energy appear??? Heat!

The Law of Conservation of Energy The First Law of Thermodynamics is yet another way to state that energy is neither created nor destroyed, but may be transferred or transformed- The Law of Conservation of Energy

2nd Law, The Law of Entropy: Natural processes always increase entropy. Entropy: disorder

What does “entropy” have to do with heat?? … Go back to the Kinetic-Molecular Theory: The faster atoms are moving, the more “disorder” or ENTROPY they have. So, if you increase the temperature of a substance, you also increase its ENTROPY.

Just like water flows naturally from high elevation to low elevation, heat flows naturally from warmer temperature to cooler temperature. Heat will never of itself flow from a cold object to a hot object. You can make water move from low elevation to high elevation if you use a water pump, which requires an input of energy. You can make heat flow from a cooler object to a warmer object if you use a heat pump, which requires an input of energy. Heat pumps are used in your refrigerator and in the heating/air conditioning system in houses!

Different kinds of heat pumps: Refrigerators remove heat from food and transfer the heat to the outside.

3rd Law: It is not possible to lower the temperature to absolute zero. Since absolute zero is the temperature at which a gas would exert zero pressure- which is impossible, reaching 0 Kelvins is impossible also.