• SkillCat Team

Essential Chemistry

Updated: 7 days ago

EPA 608 Core Chapter 10 (Take full course for free)


In this module, we will go over concepts in chemistry that will help you better understand how HVAC systems work.


1. Atoms and Molecules


Recall that an atom is the basic building block of all things. Everything around us can be broken down into their smallest unit of atoms. You can think of atoms as lego blocks that can be arranged to form everything we see around us.


Clusters of atoms are known as molecules. If atoms are lego blocks, molecules would be a stack of lego blocks in a particular quantity and order.


For example, a water molecule, H2O, is made of

- Two hydrogen atoms, and

- One oxygen atom.


This particular arrangement of two hydrogen atoms and one oxygen atom is what makes the molecule water. If we had two hydrogen atoms and two oxygen atoms, this molecule would no longer be water. So it is the unique combination of atoms that makes the molecule what it is.


2. Physical States of Matter


Everything in the world is made of matter, from your TV, to the oceans, to the air you breathe. Matter is anything that has a volume and a mass. Matter is made up of atoms and molecules.


Matter exists primarily in three states:

- Solid

- Liquid

- Vapor (Gas)

Note that gas and vapor refer to the same state of matter. For purposes of the EPA exam, we will refer to this state as just vapor.



The melting point is the temperature at which a solid changes to liquid. For example, the melting point of ice is normally 32°F. This means that at any temperature below 32°F, ice will stay solid. But if the surrounding temperature is 32°F or higher, the ice will start to melt, changing state from solid to liquid.


The boiling point is the temperature at which a liquid changes to gas. The boiling point of ice is 212°F or 100°C. This means that at any temperature below 212°F, water remains liquid. For example, at a room temperature of 72°F, a glass of water is just liquid.


When we boil water, we notice that it stays liquid until it reaches 212°F, which is when it starts bubbling. The bubbling is a sign that water is changing phase to gas.


Note that 212°F or 100°C is the temperature at which pure water starts to boil. If you measure the temperature at which water boils in your kitchen, you may see that the actual temperature is a little off. This is due to the minerals like calcium that are naturally dissolved in your water.


3. Effects of Temperature


We commonly think of temperature in terms of units like Fahrenheit or Celsius.


Temperature is a measure of how fast the molecules in a substance is moving, on average.



4. Effects of Pressure


Pressure is defined as the force exerted over a certain area. Applying pressure on matter can change their properties, including their temperature.



From the previous videos, we see that as pressure increases, a substance’s boiling point increases. Conversely, we see that as pressure decreases, a substance’s boiling point decreases.


5. Conclusion


Matter exists primarily in three states: solid, liquid, and gas. When temperature is increased or decreased, a substance changes state. This occurs at the melting or boiling point. When pressure is increased, a substance’s boiling point increases.


Understanding these essential concepts will allow us to better understand the Refrigeration Cycle.

13 views0 comments

Recent Posts

See All

© LearnToDrill 2020

  • Grey YouTube Icon