The molar enthalpy of a binary mixture (blue curve) of

and

is plotted as a function of the mole fraction of component

. The end points of the molar enthalpy are the pure-component enthalpies

and

. The partial molar enthalpies

and

are obtained by drawing a tangent line (black, dashed) at the black point, which indicates the mole fraction of the solution. The intersections of this tangent with the y-axis at

and

correspond to

and

, respectively. You can change the mole fraction of

in the mixture and the non-ideal parameter, which represents deviation from an ideal solution, with sliders. For an ideal solution the non-ideal parameter is zero, and the enthalpy of the mixture is a linear function of the molar enthalpies of the pure components.