Work, Heat, Energy, and the First Law (simplified)
|Introduction||What is this thing called Thermodynamics??? | Definitions | Thermal Equilibrium and Zeroth Law | Limitations|
|First Law||Work, Heat, Energy, and the First Law | Work, Heat, Energy, and the First Law (simplied) | Derivatives | Derivatives Exercise | Reversibility, Enthalpy, and Heat Capacity|
|Second Law||Things to Think About | Observations and Second Law of Thermodynamics | Alternative Approach - the Clausis Inequality | Consequences of the Second Law | Consequences of the Second Law (simplified) | Carnot Principle - motivation and examples | Equivalence of Second Law Statements*|
|Third Law||Third Law of Thermodynamics | Consequences of Third Law*|
|Development of Thermodynamics||The Thermodynamic Network | Network Exercise | Equations of State | Thermochemistry|
* Optional Section
- Work, W
- Force acting through a distance
In most applications of thermodynamics we are mainly interested in mechanical work due to pressure of a fluid. Then the work is
where P is the pressure and V is the volume. The symbol Δ means change - in this case change in volume. The reason for the minus sign is explained below.
- Capacity to do work
- Energy transferred due to a temperature difference
- No heat transfer between a system and its surroundings
- Exothermic process
- A process which releases heat
- Endothermic process
- A process which adsorbs heat
Heat is denoted by the symbol, Q
The laws of thermodynamics are based on observations of the natural world. The first law is based on two observations concerning energy:
- Energy can be transferred between a system and its surroundings by only two ways: work and heat
- The total energy of a system and its surroundings is always constant (The conservation of energy)
These two observations can be combined into the First Law of Thermodynamics:
The internal energy of a system is constant unless changed by doing work or by heating
Often in thermodynamics we use a quantity known as the Enthalpy, H. It is defined as: [math]H=U+PV[/math]
Enthalpy is probably the most common thermodynamic quantity used, especially in chemistry and engineering. Especially common is the use of the "enthalpy of reaction". Often this is called just the "heat of reaction". There are likewise heats of solution, mixing, vaporization, etc.
- Heat Capacity
- The change in heat per unit temperature
We usually use two specific types of heat capacity:
- Heat Capacity at constant pressure, CP.
- Heat Capacity at constant volume, CV.
- Note that some references say the internal energy is the energy due to the internal vibrations, etc. In other words that other than kinetic or potential energy. However, the definition used here is equivalent and is easier to understand.
- it is actually the heat change at constant pressure. See here for details