Govt. Exams
Water has exceptionally high specific heat (~4.18 kJ/kg·K), much higher than metals (iron ~0.46) and air (~1.01). This is due to hydrogen bonding in water.
From first law: ΔU = Q - W = 500 - 200 = 300 J. Internal energy increases by 300 J.
Heat (Q) and work (W) are path-dependent quantities, not state functions. Internal energy, enthalpy, and entropy are state functions depending only on initial and final states.
A reversible adiabatic process has constant entropy (dS = 0), making it isentropic. This is a key assumption in many thermodynamic analysis for ideal processes.
The Mayer relation: C_p - C_v = R, where R is the specific gas constant. This relation holds for all ideal gases.
The correct form is dU = δQ - δW, where δW = PdV for expansion work. This represents energy conservation in thermodynamic systems.
Maximum efficiency is Carnot efficiency = 1 - (T_cold/T_hot) = 1 - (300/500) = 0.4 = 40%
In an isochoric (constant volume) process, W = ∫PdV = 0 because volume does not change.
A reversible adiabatic process is also called isentropic, meaning entropy remains constant (ΔS = 0).
In an isothermal process, temperature is constant. For an ideal gas, internal energy depends only on temperature, so ΔU = 0.