2nd Law
Whether a process can occur (energy has quality)
A Summary on the Second Law:
- Predict the direction of the processes
- Determine the best theoretical performance of the cycles, engines, and other devices
- Evaluate quantitatively the factors that preclude realizing maximum performance
Concepts of the Second Law
First Law
- Energy is conserved and the potential energy of the ball is the same as the rise in internal energy of the surroundings Second Law
- Energy is dispersed from being localized with the ball to being spread out in the surroundings (is the work useful?)
Note that there are some processes that are irreversible and the second law can help us describe that
For a process to proceed we need both the 1st Law of Thermo and the 2nd law to be satisfied.
Irreversibility
All physical processes contain irreversibilities that transform energy from a useful state (localized) to a less useful state.
Examples include:
- Heat transfer
- Fast or unconstrained expansion / compression
- Mixing of different species
- Friction
- Inelastic deformation
- Chemical reactions
The system could possibly be restored to its initial state but then would not be possible to also return the surroundings to their initial state
Reversible Processes
A process in which the system and their surroundings can be restored to their initial states after the process has taken place.
Examples
- Frictionless
- Quasi-equilibrium
- Elastic deformation Determine the best performance of devices and quantify factors which reduce performance from their maximum
Thermal Energy Reservoir
A hypothetical body with a very large thermal energy capacity that can supply or absorb finite amounts of heat without a change to its temperature.
Clausius Statement of the Second Law
A system cannot operate so that its sole outcome is heat transfer from a cold reservoir to a hot reservoir
Kelvin-Planck Statement of the Second Law
No system can transform all heat into work, there must always be some heat rejection.
Equation
Entropy uses the 2nd law.