Glossary
Closed System
A system that can exchange energy (like heat) but not matter with its surroundings.
Example:
A sealed pressure cooker on a stove is a closed system because steam cannot escape, but heat energy can be transferred to the food inside.
Entropy
A measure of the disorder or randomness in a system, or how much energy is spread out.
Example:
When a drop of ink is added to a glass of water, it slowly spreads out, increasing the entropy of the system as the ink molecules disperse.
Isolated System
A system that does not exchange energy or matter with its surroundings.
Example:
A perfectly insulated thermos containing hot coffee, if truly ideal, would be an isolated system where the total energy and mass remain constant.
Open System
A system that can exchange both energy and matter with its surroundings.
Example:
A boiling pot of water without a lid is an open system as both heat (energy) and steam (matter) can escape into the air.
Second Law of Thermodynamics
States that the total entropy of an isolated system can never decrease; it can only increase or remain constant.
Example:
A broken glass will not spontaneously reassemble itself because doing so would violate the Second Law of Thermodynamics by decreasing the total entropy of the universe.
State Function
A property of a system that depends only on its current state, not on the path taken to reach that state.
Example:
The altitude of a mountain climber is a state function; it only depends on their current height, not whether they hiked up a steep path or a gradual slope.
Thermodynamic Equilibrium
The state of a system where there are no net macroscopic flows of matter or energy, and entropy is at its maximum.
Example:
When a cold drink reaches room temperature, it has achieved thermodynamic equilibrium with its surroundings, and no further net heat transfer occurs.