# Cyclic and Non-Cyclic Processes

A cyclic process consists of a series of changes which return the system back to its initial state. In a non-cyclic process, the series of changes involved do not return the system back to its initial state.

- In case of cyclic process, as
*U*=_{f}*U*,_{i}*U*=*U*–_{f}*U*= 0_{i}*U*∝ Δ*T*.*T*= 0 - From first law of thermodynamics,
*Q*= Δ*U*+ Δ*W**Δ*i.e., heat supplied is equal to the work done by the system. [as*Q*= Δ*W,**Δ*= 0]*U* - For cyclic process,
*P–V*graph is a closed curve and area enclosed by the closed path represents the work done (Fig. 14).**Fig. 14** - Work done in non-cyclic process depends upon the path chosen or the series of changes involved and can be calculated by the area covered between the curve and volume axis on
*PV*diagram (Fig. 15).**Fig. 15**