The branch of chemistry that deals with heat and other forms of energy is known as thermodynamics. The first law of thermodynamics is about the energy conservation of thermodynamic processes. So, if we take the example of heat, it can neither be created nor be destroyed. Heat is restored to some other form of energy. A heat engine is the most common example of such a system, which converts thermal energy to mechanical energy and vice-versa.

Thermodynamics

The study of the relationship between heat, temperature, energy, and work is known as thermodynamics. The laws of thermodynamics explain how a system changes and how it works within its surroundings. 

System and surroundings

The portion of the universe considered for thermodynamic examination is known as a system. The remaining portion of the system or the portion devoid of the system is known as surrounding.

For example, if the system is one mole of gas placed in a beaker, everything outside the beaker boundary is surrounding.

The First Law of Thermodynamics

It states that the sphere energy does not change; it always remains sustained. It can neither be produced nor be destroyed. It can only be transferred from one system to another system in the universe. The law describes the change in energy states with heat transfer and work changes.

Equation of First Law of Thermodynamics

The equation which defines the first law of thermodynamics is-

ΔU = q + W

• ΔU is a change in internal energy is the heat transfer between both system and surroundings, and
• W is the total work performed.

It states that the internal energy of a system is affected by heat and work.

Examples of the First Law of Thermodynamics

• Heat engine: is the most common example. In this system, the mechanical energy converts into heat energy or vice versa. So, this system does not allow the loss of heat. And thus, no amount of energy is lost.
• Photosynthesis: It is the process used by plants to prepare food in the presence of sunlight. In the process of photosynthesis, light energy gets converted into chemical energy.
• Pendulum swinging: When a pendulum swings, it uses potential energy converted into kinetic energy. This kinetic energy is converted back into potential energy. So, zero amount of energy gets wasted.
• Burning of wood: wood-burning converts chemical energy into kinetic energy. And when burning wood transforms into ash, this kinetic energy gets transferred into heat.

The First Law of Thermodynamics for a Closed System

In a closed system, energy can be transferred between the system and surroundings, not matter.

For a closed system, the total work done is equal to the pressure applied and the change in volume of the system that happens due to the applied force.

W = -qΔV 

W is the work done on the system, q is the pressure applied, V is the change in volume of the system. We can calculate work done by using the above equation. 

The whole energy of the system remains sustained. If energy is lost by the system, it is gained by the surroundings. If the energy is absorbed by the system, it is lost by the surroundings. the equation of the energy change can be written as- 

ΔU(system) = −ΔU(surroundings)

ΔUsystem is the change in the energy of the system and ΔU surroundings are the change in energy of the surroundings.

The First Law of Thermodynamics for an Open System

In an open system, both energy and matter transfer between the system and its surroundings. An example of such a system is shaft processing.

Adiabatic process: The process in which a system does not allow any transfer of energy and matter with the surroundings. It neither loses nor gains energy, but the system’s internal energy can be changed due to the amount of work done by the system.

Isolated system: As the name suggests, the isolated system does not allow any transfer of energy and matter between surroundings and has no environmental surroundings. The energy of such a system is conserved.

Limitations of the First Law of Thermodynamics

The law states that an energy balance is maintained in a thermodynamic system. But it fails to explain the change of the state of the system and the feasibility of the thermodynamic process. All these concepts are explained by the second law of thermodynamics.

Conclusion:

The first law of thermodynamics helps us to understand the concept of conservation of energy. The law explains the concept of energy, which can neither be created nor be destroyed. The energy entering into a system is equal to the energy leaving the system, regardless of its form.