Broad Summary of Thermodynamics: Sometimes seeing the Bigger Picture helps you Put together the smaller pieces and connect the dots b/w Physics, Chemistry, and Biology.
Zeroth law (concept of temperature)
0th law of thermodynamics basically says that heat flows from hot objects to cold objects to achieve thermal equilibrium.
Mathematically, if TA = TB, and TB = TC, then TA = TC. Where T is temperature.
First law (ΔE = q + w, conservation of energy)
1st law of thermodynamics is based on the principle of conservation of energy, and it basically says that the change in total internal energy of a system is equal to the contributions from heat and work.
ΔE is the same thing as ΔU, which is the change in internal energy.
Q is the contribution from heat
Q is positive when heat is absorbed into the system (ie. heating it).
Q is negative when heat leaks out of the system (ie. cooling it).
W is the contribution from work.
W is positive when work is done on the system (ie. compression).
W is negative when work is done by the system (ie. expansion).
Equivalence of mechanical, chemical, electrical and thermal energy units
If it’s energy, it’s Joules. It doesn’t matter if it’s potential energy, kinetic energy, or any energy - as long as it’s energy, it has the unit Joules.
Energy is equivalent even if they are in different forms. For example, 1 Joule of mechanical energy can be converted into 1 Joule of electrical energy (ignoring heat loss) - no more, no less.
Second law: concept of entropy
The 2nd law states that the things like to be in a state of higher entropy and disorder.
An isolated system will increase in entropy over time.
An open system can decrease in entropy, but only at the expense of a greater increase in entropy of its surroundings.
The universe as a whole is increasing in entropy.
ΔS ≥ q / T
q is the heat transferred.
T is the temperature in Kelvin.
For reversible processes ΔS = q / T.
For irreversible processes ΔS > q / T.
Real processes that occur in the world are never reversible, so entropy change is always greater than the heat transfer over temperature.
Because of the irreversibility nature of real processes, as long as anything occurs, the entropy of the universe increases.
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