Question

Heptane (C7H16) and octane (C8H18) are constitutents of gasoline. At 80 degree celsius, the vapor pressure of heptane is 428mmHg and the vapor pressure of octane is 175mmHg. What Xheptane in a mixture of heptane and octane that has a vapor pressure of 305mmHg and 80 degree celsius?

Answer 1

Not sure what you mean by the Xheptane but i will assume you mean composition of the vapor. I would start by maybe looking at this equation P=(pa*pb)/(pa+(pb-pa))ya (where pa=vap press a and ya=vap composition a and P=total pressure) which relates vapor pressure mixture to vapor composition. This is derived using combos of Daltons and Raoults law if you are wondering.