MCAT Physics and Math 3: Concept Summary

The zeroth law of thermodynamics states that objects are in thermal equilibrium when they are at the same temperature.

... no net exchange of heat energy.

Temperature is a qualitative measure of how hot or cold an object is; quantitatively, it is related to the average kinetic energy of the particles that make up a substance.

Thermal expansion describes how a substance changes in length or volume as a function of the change in temperature.

A thermodynamic system is the portion of the universe that we are interested in observing, whereas the surroundings include everything that is not part of the system.

Isolated systems do not exchange matter or energy with the surroundings.

Closed systems exchange energy but not matter with their surroundings.

Open systems exchange both energy and matter with their surroundings.

State functions are pathway independent and are not themselves defined by a process. Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy are all state functions.

Process functions describe the pathway from one equilibrium state to another. Work and heat are process functions.

The first law of thermodynamics is a statement of conservation of energy: the total energy in the universe can never decrease or increase.

... the heat flow into the system minus the work done by the system.

Heat is the process of energy transfer between two objects at different temperatures that occurs until the two objects come into thermal equilibrium (reach the same temperature).

Specific heat is the amount of energy necessary to raise one gram of a substance by one degree Celsius or one kelvin.

During a phase change, heat energy causes changes in the particles’ potential energy and energy distribution (entropy), but not kinetic energy. Therefore, there is no change in temperature. This is the heat of transformation.

For isothermal processes, the temperature is constant, and the change in internal energy is therefore 0.

For adiabatic processes, no heat is exchanged.

For isobaric processes, the pressure is held constant.

For isovolumetric (isochoric) processes, the volume is held constant and the work done by or on the system is 0.

The second law of thermodynamics states that in a closed system (up to and including the entire universe), energy will spontaneously and irreversibly go from being localized to being spread out (dispersed).

Entropy is a measure of how much energy has spread out or how spread out energy has become.

On a statistical level, as the number of available microstates increases, the potential energy of a molecule is distributed over that larger number of microstates, increasing entropy.

irreversible

essentially reversible