This is a small confusion I have regarding steam distillation. Let us consider a sample of water mixed with an organic compound that is insoluble in water. Let us also consider that the boiling point of this organic compound is at 70 °C at atmospheric pressure and the boiling point of water is 100 °C at atmospheric pressure.
According to what I have learned and what I have researched online, it says the two compounds in the mixture evaporate separately, independent from each other. So, the total pressure of the system at a given time would be the vapor pressure of water and the vapor pressure of organic compound combined.
My confusion is that the articles online says that this combined vapor pressure is higher than the vapor pressure when only one compound is available, so, the mixture reach atmospheric pressure faster so, it boils at lower temperature than 70 °C.
How can this be possible if these two compounds (water and the organic compound) are insoluble in one another, and if these two compounds evaporate independently from each other? I cannot understand it because I have also learned that when the environmental pressure increases it also increases the boiling point of that substance. Since these two compounds are not soluble in each other and evaporate independently, should not the vapor pressure of one compound increase pressure that affects the other compounds boiling point and evaporation rather than the vapor pressures of both these compounds affecting the boiling point and evaporation of whole system of these compounds combined (Because these compounds are separate and does not have intermolecular interactions like a binary mixture). What is the mistake I made in my thought process?
Edit: For example, take benzene and water mixture and their boiling points. Pure water is at 100 °C, benzene at 80 °C, benzene + water at 65 °C. The reason suggested is that, at 65 °C, the vapor pressures are 0.23 atm for water, and 0.77 atm for benzene. The total pressure over this mixture at 65 °C is 0.23 atm + 0.77 atm = 1.00 atm. So any mixture water + benzene boils at 65 °C.
Why does this combined vapor pressure reaching the atmospheric pressure lower the boiling point of both liquids, while these two liquids are in equilibrium with their vapor independent from each other? What kind of interaction does these two liquids has that causes this?