Biothermodynamics - basics
Biothermodynamics: basic concepts. First law of thermodynamics, internal energy. Second law of thermodynamics, entropy.
Thermodynamics: basic concepts
Thermodynamics deals with the effects of temperature and energy transformation within thermodynamic systems. Thermodynamic systems are regions of a finite volume, defined by either a real or imagined boundary. Outside of this boundary is known as the surroundings. A thermodynamic system is defined by parameters such as:
- Volume
- Pressure
- Temperature
- Internal Energy
- Enthalpy
- Entropy
- Concentration
Thermodynamic systems can be:
- Isolated systems (no exchange of energy or matter between system and external space)
- Closed systems (exchange of energy but no exchange of matter between system and external space)
- Open system (exchange of energy and matter between system and external space)
Isolated and closed systems are always idealised as no system is indefinitely isolated or closed.
An important term in thermodynamics is that of thermodynamic equilibrium. This is the state a thermodynamic system is in if these parameters do not change with time (must therefore be an isolated system). Thermodynamic equilibrium is the most probable state of a system to be in.
First law of thermodynamics (you can’t win)
The total energy of a system is conserved. Energy in nature is not created or destroyed, it only passes from one form to another, or between bodies. The total sum of energy is constant. This is also known as the law of energy conservation. The equation for this is:
dU is change of internal energy \deltaQ is amount of heat added to system \deltaW is work performed by system
Second Law of Thermodynamics (you can’t even break even)
The entropy of an isolated system never decreases, it only ever increases or remains constant. Additionally, all processes tend to increase in entropy over time, moving to a state of disorder. In other words, isolated systems tend towards disorder, not order.
The best illustration for this is if you consider releasing a can of gas inside a box, the gas will expand throughout the box, it will never spontaneously go back into the can.
We can define entropy as the quantity of energy within a system unavailable for work, often seen as the degree of disorder or randomness in a system.
The Boltzmann definition of entropy is: