what does it mean to do work on a system? Also, what is “heat” (q)? what is internal energy (U)?
*in my knowledge*, work is a *something* that is used to transfer energy from one *something* to another. And “q” is the heat absorbed or released by the system. U is the energy existing inside the system…
“But I can’t really build good intuition around it!!!”
Like, i think there is a gas prolly…in the system. So, it has a energy called “U” but where did it come from? what does it mean to have energy? I have a LOTS of little doubts like this that i have to clear to understand further topics better.
In: 1
I’m a student in physical chemistry, will try this one :>
*Internal energy* is defined as the energy of system **excluding** any part of energy that’s based on external fields like gravity or electric field (potential energies). *Heat* was defined as “energy transferred between systems because of the difference of temperature”, and any other ways of energy transfer would be *Work.* Your impressions about these 3 notions in thermodynamics is basically right.
With all these definitions in mind, try imagine a well-sealed and heat insulate syringe with some air in it. If you press it in for some distance, the gas in it would be compressed (ΔV<0) and the pressure (p) would be risen to the point where the pressure inside and outside are the same. In this kind of process heat (Q) is zero, and the work (W=-pdV) is greater to zero, as internal energy (U) is the sum of both heat and work, you’ll find the internal energy of system was increased in this process, which would be shown intuitively as this syringe now has more energy, like a compressed spring.
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