Practice question

**First law of thermodynamics** ΔU = Q - W, ΔU internal energy change (J), Q heat added to system (J), W work done by system (J), sign convention physics Q positive when added, W positive when done by system, energy conservation, for isochoric W=0 ΔU=Q, for adiabatic Q=0 ΔU=-W, for isothermal ΔU=0 Q=W, for cyclic ΔU=0 Q_net=W_net. First Law: Δ Q = Δ U + Δ W . Δ Q = 690 , Δ W = -210 (work on system). 690 = Δ U - 210 ⇒ Δ U = 690 + 210 = 900 J . Using first law ΔU = Q - W,