First Law of Thermodynamics
Return to the Thermodynamics Page.
The First Law of Thermodynamics
is almost the same thing as the
Law of Conservation of Matter.
It deals with energy exchanges between a system and its surroundings.
The total internal energy in a system is the sum of all the kinetic
energies and potential energies of its particles.
Esystem = (KE)system + (PE)system
We cannot determine the value of Esystem, but we can measure the changes in E.
E = Efinal - Einitial
Or for a chemical reaction:
E = Eproducts - Ereactants
The sum of the heat absorbed or released and the work done on or by the system is the change in E.
E = q - w
When q is positive, heat is absorbed by the system.
When q is negative, heat is released by the system.
When w is positive, work is done by the system.
When w is negative, work is done on the system.