Energy, Entropy, and Free Energy Notes

The First Law of Thermodynamics states that the energy of a closed system is constant.
Energy does not flow into or out of a closed system.
Since the universe is a closed system, the total energy of the universe is constant.
If a system within the universe is open to other systems, its energy can increase or decrease as energy flows into or out of it.
The energy of an open system can change due to inflows or outflows of energy, but the total energy of the universe remains constant.
Energy from the sun warms the Earth, increasing its energy. This energy is transformed into food for life on Earth.
This transformation doesn't violate the first law because the total energy of the universe remains unchanged. Only the form and location of energy change.
Earth is cooled by radiating energy into outer space.
Energy enters Earth from the sun and then leaves Earth to enter outer space, resulting in a relatively constant total energy for Earth.
Changes in inflows or outflows can cause slight variations. For example, greenhouse gases delay the exit of energy, increasing Earth's energy and temperature.

The constancy of energy is insufficient to explain our world.
Even with constant energy, the amount of energy available to do useful work generally decreases over time.
Entropy measures the energy in a system that cannot do useful work.
Consider a rock on a cliff: initially, it possesses potential energy.
After falling, the potential energy transforms into sound, heat, and vibration.
Eventually, all potential energy becomes heat in the rock, ground, and air.
Energy remains constant, but the ability of the energy in the system to do work decreases.
To drive a stake into the ground, dropping a rock on the stake works better than dropping it next to the stake and using the dispersed heat.
Energy is critical but insufficient to understand the world; entropy is a key missing element.
Entropy is a measure of the amount of energy which has been dispersed and is not readily available to do work.
Energy is not destroyed or reduced, but dispersed.
The second law of thermodynamics states that the entropy of the universe, as well as any closed system, can only stay the same or increase over time.
Entropy can never decrease in a closed system.
In any real closed system, the entropy will increase over time, so the useable energy decreases over time.
However, entropy can decrease in a system if it increases by a greater amount in another system, as long as it increases in total.