Physical and Chemical Properties, Changes, and Energy Continuity

Vocabulary flashcards covering physical vs. chemical properties and changes, scientific reversibility, energy conservation, and the continuity equation.

Physical Property

A property that is measurable without destroying the sample and is repeatable, such as mass.

Chemical Property

A property that can only be measured by destroying the sample, making it a one-time-only measurement (such as flammability or combustibility).

Color

A physical property that usually signals a chemical change when an alteration occurs.

Physical Change

A change that is reversible in the strict scientific sense.

Chemical Change

A change that is irreversible.

Scientific Definition of Reversible

A change is reversible only if, at every infinitesimal step along the reaction coordinate, there is no net preferred direction toward the initial or final state, meaning every intermediate position is a position of equilibrium.

Reaction Coordinate

A variable proportional to time (rather than linear clock time) that measures progress along a transformation or reaction path.

Equilibrium

A state at a given point along a reaction coordinate where there is no preference to move forward or backward.

Energy

A conserved quantity generated by time-translation symmetry.

Kinetic Energy Formula

$\text{Kinetic energy} = \frac{1}{2}mv^2 = \frac{3}{2}kT$, where $k$ is Boltzmann's constant and $T$ is in Kelvin.

Conservation of Energy

The law stating that the rate of change of total energy (kinetic plus potential) equals $0$.

Continuity Equation

An equation that closes the loophole of energy being "beamed in" by locally tracking energy accumulation and spatial transport, making energy conservation a robust, local statement.

Accumulation Term

The term in the continuity equation ($\frac{\partial U}{\partial t}$) that tracks local building up of energy density.

Transport Term

The Laplacian/divergence term in the continuity equation ($\nabla \cdot (pv)$) that tracks energy moving through space.

Exothermic Reaction in Continuity Terms

A reaction ($A + B \rightarrow C + \text{energy}$) where energy accumulates locally during the reaction and, once ended, accumulation stops and energy is transported away by increasing the momentum of surrounding molecules.