Answer:
What is the first law of thermodynamics?
Many power plants and engines operate by turning heat energy into work. The reason is that a heated gas can do work on mechanical turbines or pistons, causing them to move. The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system. The first law of thermodynamics states that the change in internal energy of a system \Delta UΔUdelta, U equals the net heat transfer into the system QQQ, plus the net work done on the system WWW. In equation form, the first law of thermodynamics is,
\Large \Delta U=Q+WΔU=Q+Wdelta, U, equals, Q, plus, W
Wait, why did my book/professor use a negative sign in this equation?
Here \Delta UΔUdelta, U is the change in internal energy UUU of the system. QQQ is the net heat transferred into the system—that is, QQQ is the sum of all heat transfer into and out of the system. WWW is the net work done on the system.
So positive heat QQQ adds energy to the system and positive work WWW adds energy to the system. This is why the first law takes the form it does, \Delta U=Q+WΔU=Q+Wdelta, U, equals, Q, plus, W. It simply says that you can add to the internal energy by heating a system, or doing work on the system.
What do each of these terms (\Delta U, Q, WΔU,Q,Wdelta, U, comma, Q, comma, W) mean?
Nothing quite exemplifies the first law of thermodynamics as well as a gas (like air or helium) trapped in a container with a tightly fitting movable piston (as seen below). We'll assume the piston can move up and down, compressing the gas or allowing the gas to expand (but no gas is allowed to escape the container).
