Energy can never be created or destroyed, only transformed.
This means that there is only so much energy in the universe. You can't create more and you cannot, under any circumstances, destroy what is there. The First National Energy Bank of the Universe has one set amount of energy in its account. The energy can change from one form to another, say from solar to electrical, but the total amount of energy never ever changes.
"You can't win," people often say of the first law. No matter what you do in an exchange of energy in this universe, you will First Law of Thermodynamics never ultimately come out ahead, because a greater amount of energy will never be created. Another way of stating the first law is that there is a conservation of energy in the universe. Energy, or the capacity to do work (which is a force moving something a distance), is not created or destroyed, it is conserved.
Now you know the first law of thermodynamics.
Before we travel to the second law, I want to introduce another equation, E = mc2. Along with the conservation of energy in the universe, there is also a conservation of matter. Matter First Law of Thermodynamics can never be created or destroyed. Einstein's famous equation shows the relationship between energy and matter. The E in the equation stands for energy. The m stands for mass. The c stands for the speed of light. Energy = moss times the speed of light squared. The speed of light is a constant. It never changes. No matter what the circumstances in the universe, the speed at which light travels never changes. That speed is 186,000 miles per second. So the equation E = mc2 says that the energy that any object in the universe possesses is the First Law of Thermodynamics object's mass times the speed of light squared. A beer can has this much energy:
E = (mass of beer can) times the speed of light squared. If you do the mathematics, the amount of energy in any object (its mass energy) is astounding. This equation is that simple and that incomprehensible.
We see no visible effects of the energy contained in the things around us, so it doesn't seem to make much sense. Think of any piece of matter in the universe, say, a thimble, having an insane amount of energy reserves, but there is never a withdrawal First Law of Thermodynamics from its energy bank, and there is never a deposit to its energy bank. The thimble has a huge reserve of mass energy that just sits there like a hidden Swiss bank account. Is this crazy and vast amount of mass energy ever released from matter? Yes, but rarely. An example of mass energy release is found in nuclear bombs and nuclear power. One of our only rare glimpses of this energy is the tremendous amount released in a nuclear event.
Because the speed of light, c, never changes, there is always a direct correlation between energy and mass. Energy First Law of Thermodynamics = mass x a constant (the speed of light squared). Just as there is conservation of energy in the universe, so there is a conservation of mass; the correlation between energy and mass stays equal. The first law.
("Excuse me, I really just want to improvise.")