First Law of Thermodynamics Limitations

Energy is a conserved quantity that must be transferred to a physical system to perform a particular task. It implies the capacity to accomplish a specific task. Thermodynamics is a Greek word and is made up of two words- Thermo + Dynamics, where,

Thermo means heat, and dynamics means motion, so thermodynamics translates to motion or flow of heat. Thermodynamics is the branch of science that studies energy, energy transformation, the relation between work, energy, heat and temperature. In a larger context, thermodynamics focuses on converting energy from one form to another and transmitting energy from one composition to the other.

Thermodynamics is only concerned with the interconversion of energy, not with the cumulative energy of the body.

The ‘Father of Thermodynamics’ is often alluded to as Nicolas Leonard Sadi Carnot.

The study of thermodynamics is wholly based upon the generalisations derived from the first, second and third laws of thermodynamics.

First Law of Thermodynamics

This law stipulates that energy cannot be created or destroyed. It can only be changed from one particular state to the next.

The total energy constituted by the universe is constant.

When one kind of energy disappears, another form of energy appears.

A perpetual motion machine is impossible to build, which can give output without consuming energy.

Although the energy changes from one form to another, the total energy of an isolated system remains constant. When a system is changed from initial state to final state, it changes the internal energy from E to E. Thus, E can be written as:

ΔE= Ef+Ei 

The change in the internal energy can be brought about in the following two ways- Either by absorption or evolution.

By doing work on the system or work done by the system. Now, consider a system whose internal energy is E1. If the system is supplied with q amount of heat, the system’s internal energy will become E1+ q. If work w is also done on the system, the final internal energy becomes E2. Hence, 

E2= E1 + q +w 

E2– E1= q + w 

ΔE = q + w

The aforementioned equation is the correct mathematical equation for the first law of thermodynamics. 

For example,

The kinetic energy can be converted into heat energy when a driver presses the brakes to decrease the car’s speed. Here, the energy is not destroyed, but the kinetic energy present due to the car’s motion is converted into heat energy. 

The first law of thermodynamics Importance:- 

• This law is fit for all the processes in nature.
• The first law of thermodynamics first established internal energy.
• It also highlights that if we want to get some work from a machine, we need to fuel it with equivalent energy.
• This law is the restatement of the law of conservation of energy.
• This law also contributes to establishing a relationship between work and heat. According to this law, the internal energy of any system can be increased by either supplying heat to it or by making efforts on the system or both. 

The first law of thermodynamics limitations

Importance:

• The first law establishes the relationship between work done and heat absorbed while doing that work, but it fails to specify the direction of flow of heat which is a significant drawback of this law.

Example- We cannot extract heat from a cube of ice by cooling it to low temperatures. It requires some external work. On a practical note, it is not possible to convert the heat energy into an equivalent amount of work.

1. b) It does not specify the feasibility of the reaction.

Example- When a rod is heated from one end, an equilibrium has to be obtained, which is only possible by some release of energy. It does not talk about the entropy of the system.

1. c) It also fails to tell about the final temperature of two bodies when they are in contact.

To overcome the limitations of the first law of thermodynamics, another law was established, known as the second law of thermodynamics. In simple words, this law tells us that things at high temperatures will surely cool if we do not do anything to stop them. That means the direction of heat flow is from lower to higher entropy. 

Conclusion

The first law of thermodynamics is primarily a restatement of the conservation of energy principle, which claims that energy cannot be created or destroyed. It can only be converted and changed from one form to another. 

This law applies to all the three phases of matter, i.e., solid, liquid and gas. However, a few limitations, like the failure to specify the direction of heat flow, led to the establishment of the second law of thermodynamics by Rudolf Clausius and William Thomson(Kelvin).