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The First Law of Thermodynamics

According to the first law of thermodynamics, energy is neither created nor destroyed, which also implies that the total energy present in the whole universe is constant. Based on this law, we can say that the energy is just taken from one form and converted to another form. This is exactly what we are doing when we are burning fuels such as gasoline to get sufficient energy to run the internal combustion engine, or when we are using nuclear reactions to turn the turbines of a nuclear power plant to make electricity.

Basic Aspects of Thermodynamics

First, let's talk about internal energy. Internal energy of a substance is the total energy present in the particular quantity of that substance. For a chemical reaction or a physical change of reactants, the change in internal energy (ΔE) of the reactants is expressed as follows:
Change in internal energy,
ΔE = Final internal energy (Efinal) – Initial internal energy (Einitial)
ΔE Q + W
Here, Q represents the heat and W represents the work done.


Based on the above equation, these conventions are followed:
When heat is absorbed by a system, heat (Q) is positive.
When heat is given off by a system, heat (Q) is negative.
When work is done on a system, work (W) is positive.
When work is done by a system, work (W) is negative.

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