The First Law of Thermodynamics
There are three fundamental laws of thermodynamics. The first law is simply a statement of conservation of energy applied to the system. If an amount of thermal energyis given to the system, either
The internal energy U of the system can increase by an amount
It can do an amount of workon its' surroundings.
It can do a combination of the above.
Since energy is conserved,
The following must be noted:
Each of the quantitiesandin the equation above is considered from the systems point of view.
If is positive, then the system gains thermal energy and ifis negative the system loses thermal energy.
Ifis positive, the internal energy of the system increases. If the system is a gas, then the temperature of the gas increases. Conversely ifis negative the internal energy of the system is decreasing. If the system is a gas, the temperature of the gas is falling.
Ifis positive then the system is doing work on the surroundings – a gas is expanding for example. Ifis negative the surroundings are doing work on the system. W is negative.