ANS:C - the fraction vaporised but not the product composition.

If Raoult's law is obeyed, changing the feed composition of a binary mixture that is flash vaporized at a fixed pressure and temperature would affect:

• Neither the product composition nor the fraction vaporized.

1. Raoult's Law: According to Raoult's Law, for an ideal binary mixture, the partial pressure of each component in the vapor phase above the mixture is directly proportional to the mole fraction of that component in the liquid phase. Mathematically, for component 𝑖i, Raoult's Law can be expressed as:

• 𝑃𝑖Pi​ is the partial pressure of component 𝑖i in the vapor phase.
• 𝑥𝑖xi​ is the mole fraction of component 𝑖i in the liquid phase.
• 𝑃𝑖∗Pi∗​ is the vapor pressure of pure component 𝑖i at the given temperature.

2. Flash Vaporization: Flash vaporization involves rapidly reducing the pressure of a liquid mixture to a lower pressure, causing a portion of the liquid to vaporize. This process is typically conducted at constant temperature. During flash vaporization, the composition of the vapor phase and the liquid phase reach equilibrium according to Raoult's Law.
3. Effect of Changing Feed Composition: Since Raoult's Law dictates that the vapor and liquid phases reach equilibrium based on the composition of the liquid phase, changing the feed composition would indeed affect the composition of the vapor and liquid phases during flash vaporization. However, the fraction vaporized, which is the ratio of the moles of vapor formed to the total moles in the feed, remains constant because the process is conducted at a fixed temperature and pressure.