Calculating Vapor Pressures of Mixtures

Component	% vol. at 70°F	lb/gal. at 70°F	lb. per 100 gal. at 70°F	% mass
	a	b	c =a * b	d = 100 * c / total c
Ethane	0.57	3.200	1.824	0.41
Propane	30.94	4.175	129.175	28.69
Isobutane	62.69	4.646	291.258	64.70
N-butane	5.80	4.817	27.939	6.20
Totals	100.00		450.196	100.00
Component	Molecular mass	lb.mols/ 100 gal.	Mol fraction	Vapor pressure at 70°F absolute, psi
	e	f=d / e	g = f / total f	h
Ethane	30.068	0.061	0.007	570
Propane	44.094	2.93	0.345	124
Isobutane	58.120	5.011	0.591	46
N-butane	58.120	0.481	0.057	31
Totals		8.483	1.000
Component	Partial Pressure absolute, psi		Composition of vapor in equilibrium with liquid % by vol.
	i=g * h		j = 100 * i / total i
Ethane	3.99		5.27
Propane	42.78		56.50
Isobutane	27.19		35.90
N-butane	1.77		2.33
Totals	75.72		100.00