For a steady flow process, the first law of thermodynamics deals with the conservation of:

Explanation:

First law of thermodynamics

• The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.
• The law of conservation of energy states that the total energy of an isolated system is constant.
• Energy can be transformed from one form to another but cannot be created or destroyed.
• The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings

δQ = ΔU + δW

ΔU = δQ - δW

According to first Law of thermodynamics, “For a closed system undergoing a cycle, net heat transfer is equal to network transfer.”

ΣQ = ΣW

Additional Information 
Zeroth law of thermodynamics: 

• If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Third law of thermodynamics: 

• As the temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

ΔST = 0K = 0

The second law of thermodynamics:

• The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.

ΔSTotal = ΔSSystem + ΔSsurrounding

• The second law of thermodynamics actually deals with the quality of the energy. As per the second law of thermodynamics whenever low-grade energy transfer from one state to another state some randomness get associated with the energy and the quality of energy get degraded.
• The second law of thermodynamics introduces the concept of entropy.