Lesson 1: Intro to Thermodynamics
Thermodynamics is the study of the laws that govern the transfer of energy and matter within
and between systems. The first law states that energy cannot be created or destroyed, only
changed form. The second law states that entropy will increase over time in any closed system.
The third law states that an open system will allow the transfer of mass and/or heat across its
boundaries, thus maintaining a state of equilibrium. A coffee cup is a simple example of a
system undergoing thermodynamic change, with everything inside the cup considered as my
surroundings. The universe outside of the cup is considered the surroundings for the coffee
cup, and an open system allows for the transfer of mass and/or heat across its boundaries.
Lesson 2: Thermodynamic Properties
In thermodynamics, properties such as temperature and pressure can be used to describe a
system macroscopically and microscopically. Intensive properties allow us to find all of the
states that those properties define a system completely. There are certain names that we can
give to processes to make them more easily recognizable. For instance, isobaric or isobarics
would be one name for processes that occur at the same pressure and volume. Other names
that are used include adiabatic, cycle, and pv diagram. Heat are not necessarily the same in
thermodynamics as pressure and temperature. A cycle means something that goes around and
is used to describe systems that exchange energy.
Lesson 3: Units!
In Thermodynamics, we use two types of unit: SI unit, and US customary unit. In terms of
length, the SI unit is meter. For US customary unit, it is a little bit different.We can use these
units to describe other units. For example, pressure is force over area in SI unit, and this can be
denoted as a Pascal (Pa).We also have power, which is work over time, denoted as Watt
(W).Units are very important, and we should be aware of the unit of measurement we are
using.
Lesson 4: Properties of Pure Substances
A pure substance is a substance that has a fixed chemical composition. It’s important to note
that a pure substance might be composed of more than one chemical. For example, helium is a
pure substance. It’s also important to note that a pure substance can also be in more than one
state. So, ice water, for example, has both solid water and liquid water inside of it. Ice water is
made of both hydrogen and oxygen, so that can also be considered a pure substance. If I have
water at one atmosphere, I’m going to keep the pressure constant, but I’m going to vary the
temperature. Let’s say my temperature is T4. By the way, this is a unit of pressure,
atmospheres. A few things can be going on here. I can either have a saturated liquid, which is
like the water has just begun boiling and the first drop of liquid has just started boiling into a
gas. A saturated liquid is where the last drop of water is just about to evaporate. This is just
where the liquid compressed liquid water has become a superheated vapor. After this thing
reaches saturation, it doesn’t just stop. It doesn’t just keep increasing in temperature. It stays
constant at temperature until it reaches its boiling point. Here we’re going to have boiling
taking place.
As you keep the temperature constant and reduce the pressure, your substance will tend to
start boiling. If we arrange it as before, we get something like this:We will now delve into an
aspect called quality. In summary, quality favors the vapor over the compressed liquid. When
we move from here, it will increase from 0% to 100% when it reaches the saturated vapor state.
After that, we will have a superheated vapor where the quality will always remain. Stay tuned
to learn more about this. Thank you for watching.