 # Heat capacity, Molar heat capacity and Hess's law of constant heat summation

Heat capacity (CM) :
Energy required to raise in the temperature of 1mole of substance by 1ºC
CV = Heat capacity at constant volume
CP = Heat capacity at constant pressure
C_{V} = \frac{q}{dT} = \left(\frac{dE}{dT}\right)_{V}
C_{P} = \frac{Q}{dt} = \left(\frac{dH}{dT}\right)_{p}

Relation between Cp and CV :
CP − CV = dH − dE
CP − CV = dE + PdV − dE
CP − CV = P.dV ⇒ CP − CV = R

Poisson's ratio (γ) :
\gamma = \frac{C_{P}}{C_{V}}

 CV CP \gamma = \frac{C_{P}}{C_{V}} Mono atomic gas(He, Ne) \frac{3}{2}R \frac{5}{2}R 1.66 diatomic gas (O2, H2, N2) \frac{5}{2}R \frac{7}{2}R 1.4 Poly atomic (CO2, SO2, CH4) 3R 4R 1.33

Note : q = nCV.dT (constant volume)
q = nCPdT (Constant pressure)

### Part2: View the Topic in this Video from 0:13 to 7:17

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1.Molar heat capacity, at constant pressure,
Cp = cp × M

2. Molar heat capacity, at constant volume,
CV = cV × M

3. According to Hess's law ,
ΔH = ΔH1 + ΔH2 + ΔH3