For an isobaric thermal expansion, d p = 0 , so that p d V m = R d T and the isobaric thermal expansion coefficient is: α α V ≡ ≡ 1 V ( ∂ ∂ V ∂ ∂ T ) p = 1 V m ( ∂ ∂ V m ∂ ∂ T ) p = 1 V m ( R p ) = R p V m = 1 T which is a strong function of temperature; doubling the temperature will halve the thermal expansion coefficient.