Question

State the first law of thermodynamics. mention its limitations

Answer 1

The first law of thermodynamics is the simple the law of energy conservation. It says the energy you provide to any system will be used in two ways: 1)change of internal energy, 2) work done by the system. If it is a constant volume process, then the work done is zero (because there is no displacement). So, all the heat provided will be spent in increasing the internal energy of the system. And vice versa. So it is the conservation of energy. It says how energy (heat) is transform into different form.

The limitation of the first law of thermodynamics is, it does not say anything about the direction of the flow of heat.Suppose, heat always flows from high temperature to low temperature region. If we want the opposite, we have to do some work. First law of thermodynamics does not confirm that.

First law of thermodynamics does not say anything whether a process is spontaneous or not. For any chemical reaction, the direction of the reaction (forward or backward) depends on the gibbs free energy and it is closely related to the definition of Entropy, and the essence of the entropy comes from the second law of thermodynamics. First law of thermodynamics does not address this issues.