Hello everyone, thanks for stopping by for another chemistry post. Today I'll be discussing Enthalpy.
Why you should understand Enthalpy:
Enthalpy is very important to thermodynamics and explains a lot of events in the real world that pertain to the transfer of energy or heat.
Key Ideas
- What is Enthalpy
- How is Enthalpy exchanged from place to place
- Examples
What is Enthalpy
Enthalpy (represented by H) is the energy exchange associated with a change in temperature. This could also be called a change in heat energy. However, recall from my post about State Functions that heat is not a state function while Enthalpy is.
It is important not to confuse the concepts of heat and Enthalpy, because though they seem very similar they behave very differently due to one being a state function while the other is not. Enthalpy is a state function which means that Enthalpy predictably can be measured by the beginning and ending values. However, heat relies on the path that the change in temperature travels through.
How is Enthalpy exchanged from place to place
Have you ever really thought about why ice melts? Neither had I until I took chemistry.
All I knew was that Ice melts when I put it in the freezer but when I take it out, the ice melts. When you break Enthalpy down into these easy to make observations, it's not so scary.
The idea of how energy is transferred in the form of heat is something we all witness, even if we don't recognize it.
When ice is put in an environment that is warmed than the ice itself, it melts. Heat energy is being transferred from the area around the ice to the ice itself. This brings up an important side note, how do we define where the energy is coming from and going to in a way that all scientists can understand?
Well smarter people than I already figured that one out too. The area around the ice that contains heat energy is called the surroundings. While the ice, which is the object I'm focusing on, is called the system.
So in my case of ice melting, Enthalpy is being transferred from the surroundings to the system. I could also say that the system is gaining Enthalpy from the surroundings. Either way works.
Additionally, you can define your system and surroundings however it makes sense to you. If I want to say my Sun is my system which is losing Enthalpy to my surroundings which are my Ice, that's totally cool. The important part is that you keep your Enthalpy directions consistent. Enthalpy will always move from an area of high enthalpy to low enthalpy unless there is an outside source of energy acting on it.
Examples
Below I have several examples of Enthalpy exchange. I'll be defining my system and surroundings and explaining the Enthalpy transfer between the two. I've also explained this in my youtube video linked below, in case you'd rather listen to me explain these examples.
An Ice pack on an ankle:
We've all been there. Sprained that ankle while sprinting for the cookie dough in the fridge and now we're sitting on the couch nursing that ouchie. No? Just me? Oh well. At least the cookie dough is good.
In this case, I'd describe my ice pack as my system and my ankle as my surroundings. The ankle is warmer (body temperature or higher) which means Enthalpy will move from my ankle to my ice pack. This means Enthalpy is moving from the surroundings to the system, warming the system up.
Condensation on a window:
If you've read my State of Matter post, this one should make lots of sense. Condensation is the idea that gas is turning into a liquid because of a decrease in temperature. This means that the air is warmer than the glass if condensation forms on the glass of a window. If my air is the surroundings and my window is my system, Enthalpy is moving from the surroundings to the system.
Tea Cooling:
If my tea is my system and my air is the surroundings, my hot tea will cool down. This means my hot tea is losing enthalpy. Enthalpy is being transferred from the system to the surroundings.
Lighter:
My lighter is my system and my atmosphere is the surroundings. My lighter is giving off Enthalpy which means Enthalpy is being transferred from the system to the surroundings.
Summary
- Enthalpy (represented by H) is the energy exchange associated with a change in temperature.
- The system is the item of focus, while the surroundings are the area around the system (within reason).
- Enthalpy will always move from an area of high enthalpy to low enthalpy unless there is an outside source of energy acting on it.
I hope you've found this post helpful. If you have questions feel free to message me or comment on this post. I've also included my youtube video in this post in case you'd rather listen to me talk about Enthalpy.
- Saren
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