What is the primary condition for a system to be in mechanical equilibrium?
**Isobaric process** constant pressure, work W = P ΔV = P(V₂ - V₁) = n R ΔT, for expansion ΔV positive W positive, for compression negative, heat Q = n C_p ΔT, ΔU = n C_v ΔT. Isothermal process constant temperature ΔU=0, work W = n R T ln(V₂/V₁) = n R T ln(P₁/P₂), Q = W, heat absorbed equals work done. Mechanical equilibrium in thermodynamics requires no net force or pressure difference across the system, ensuring no macroscopic motion (e.g., piston movement). This is distinct from thermal equilibrium (equal temperature). Using first law ΔU = Q - W, W = ∫ P dV, isobaric
Ref: NCERT > Physics Book > Thermodynamics > Isobaric and Isothermal Processes Work Calculation