# I am using the Redlich Kwong equation of state and I see that there is an option forRedlick Kwong polynomial for Heat Capacity. What is this and how is theRedlich Kwong Heat Capacity calculated?

 The Redlich-Kwong heat capacity is calculated from the zero pressure polynomial valid for ideal gasesusing analytical derivatives of the RK equation of state and the fundamental thermodynamicrelationships between state variables.The ideal gas heat capacity is a function only of T. The RK heat capacity depends upon pressureand temperature. A table of values is calculated over the default range of the Redlich Kwong library, orby the range that the user has set in the GUI.Since the RK equation of state is not explicit in V, the The procedure followed is this:Cp is computed using this general relationship:Cp = Cv + v*T*beta^2 / kappaBeta and Kappa are estimated from analytic derivativesof the EOS,(dp/dT)_v and (dp/dv)_T.beta = -1/v * (dp/dT)_v / (dp/dv)_TKappa = -1/v * 1 / (dp/dv)_TCv is given by:Cv = (du/dT)_vand u (internal energy) is given by:u(T) = integral[T=T_ref:T=T] Cvo(T) dT+ integral[v=v_ref:v=v] [T*(dp/dT)_v-p] dp(du/dT)_v is taken analytically and Cvo(T) is calculatedusingCvo(T) = Cpo(T) - RwhereCpo(T)/R = a1 + a2*T + a3*T^2 + a4*T^3 + a5*T^4is the ideal gas Cp polynomial for which the user provides the 5 "a" coefficients.

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