Which of the following statements most accurately describes the first law of thermodynamics?

a. Energy can neither be created nor destroyed, but it can be changed from one form to another.

b. One usable form of energy cannot be completely converted into another usable form.

c. One usable form of energy can be completely converted into another usable form.

d. Energy cannot be created or destroyed. Energy cannot be transformed.

a. Energy can neither be created nor destroyed but can be changed from one form to another.

Explanation:

The first law of thermodynamics was stated around 1850 by Rudolf Clausius and William Thompson. This law states that "energy can neither be created nor destroyed but can be transformed/changed from one form to another". The law is actually an application of the "law of conservation of energy".

More formally, the law states that the internal energy of an isolated system is always equal to the work done on or by the system, plus or minus the heat that flows in or out of the system.

Common application of the law is;

In heat engines where thermal energy is converted to mechanical energy and vice-versa.

The first law of thermodynamics relates the work and heat transferred exchanged in a system through a new thermodynamic variable, internal energy. This is basically a principle that reflects the conservation of energy in the context of thermodynamics. In simple words: the total energy of the universe remains constant. It is not created or destroyed, it only transforms.

Therefore the correct answer is A. Energy can neither be created nor destroyed, but it can be changed from one form to another.