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- Thermodynamics: the science of changes in energy and matter.
Thermodynamics is used to predict what reactions will occur and in what direction.
Keywords of thermodynamics:
o Energy.
o Heat.
o Work.
- Energy (U): the capacity to change something (Joule (J)). Energy can be transformed
in different ways.
Heat and work are ways to transform energy.
- Heat (Q): expression of the kinetic energy of molecules (J),
measured by temperature (K).
- Work (W): force * distance (mechanical) (J or Nm). Work can also
be electrical, chemical, magnetic, etc.
U =Q+ W
o Note that when the system is doing work, instead of work being done in the
system, the following formula is used: U =Q−W .
The first law of thermodynamics describes the faith of energy in a system.
- First law of thermodynamics: energy (U) is never lost in a system and its
surroundings. It can only be converted from one form to another, or you can transfer
it.
When energy disappears in one form, it appears in another form.
Since the first law of thermodynamics states that energy in a system is constant, this
means that Q+W is constant too.
o Often, energy is converted into heat, instead of useful work.
Energy (U) is a state function, as it only depends on the beginning and end state of a
system.
o Work and heat are not state functions, as they depend on the path between the
beginning and end state of a system.
Thermodynamics is about changes and not about
absolute values. Therefore, a reference state is
needed; all values used in thermodynamics are always
relative to a reference state.
As stated before, energy (U) is constant. However, it
can be transformed.
o Chemical energy motion.
o Radiant energy chemical energy.
o Electrical energy thermal energy.
Thermodynamics describes a system and its surroundings. So, when applying
thermodynamic equations on a certain system, you must define the system boundary.
The sum of the system and its surroundings is everything the complete universe.
System types:
o Isolated systems. No exchange of energy and matter with the surroundings.
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