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Introduction to Thermodynamics

Introduction

As the name implies, thermo-dynamics is concerned with changes in heat, which is one form of energy. A broader definition is that thermodynamics is the set of excepted behaviors (laws) that let us predict the possible changes in energy of a chemical or physical system. The most common forms of energy are thermal energy (heat), mechanical energy (work), mechanical potential energy, chemical potential energy, and electrical energy.

The study of thermodynamics is often divided in several related categories:

  1. Chemical thermodynamics - changes in energy during chemical reactions
  2. Process thermodynamics - changes in energy during physical processes
  3. Phase equilibria - describing the equilibrium states of systems using equations of state and phase diagrams

Nomenclature

Learn the following terms because recognizing the differences in different types of systems and processes is crucial to understanding the thermodynamic concepts.

System
The specific subset of the universe that we are trying to describe.
Phase
A portion of a system that has a homogeneous composition at the microscopic level.
Surroundings
The rest of the universe outside of the system being considered.
Open system
A system in which matter can enter and leave.
Closed system
A system in which matter is not exchanged with the surroundings.
Isolated system
A system in which neither matter nor energy is exchanged with the surroundings.
Isothermal process
A process that occurs at a constant temperature.
Adiabatic process
A process that occurs with no exchange of heat.
Intensive property
A property of a system that does not depend on the size of the system, for example, temperature, pressure, and density.
Extensive property
A property of a system that does depend on the size of the system, volume for example.

Don't Forget the Really Big Concepts in Chemistry

Kinetics describes how quickly or slowly a reaction occurs.

Thermodynamics describes the changes in the form of energy when a reaction occurs, for example, converting chemical energy to heat.

Equilibrium describes reactions in which the reactants and products coexist.


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