Dew Point Calculations Using Raoult's Law

This page focuses on dew point calculations using Raoult's law, presenting a detailed example for a binary mixture of acetonitrile and nitromethane.

Example: The problem involves determining the liquid-phase compositions (x₁ and x₂) and total pressure (P) for a mixture of acetonitrile (1) and nitromethane (2) at 75°C, given a vapor-phase composition of y₁ = 0.600.

The solution approach involves the following steps:

1. Use Raoult's law equation: y₁P = x₁P₁ˢᵃᵗ
2. Rearrange to solve for x₁: x₁ = y₁P / P₁ˢᵃᵗ
3. Use the fact that for a binary system, x₁ + x₂ = 1
4. Substitute known values and solve for P

Given:

• y₁ = 0.600
• T = 75°C
• P₁ˢᵃᵗ = 83.21 kPa (acetonitrile)
• P₂ˢᵃᵗ = 41.98 kPa (nitromethane)

Calculations yield:

• P = 59.741 kPa
• x₁ = 0.431
• x₂ = 0.569

Highlight: This example demonstrates the application of Raoult's law for dew point calculations, which are crucial in understanding phase behavior and designing separation processes.

The page emphasizes the importance of using the correct form of Raoult's law equation for dew point calculations, where the vapor-phase composition is known, and the liquid-phase composition and total pressure are to be determined.

Vocabulary: Dew point - The temperature at which vapor begins to condense into liquid at a given pressure.

This example provides valuable insight into how Raoult's law can be applied to solve practical problems in chemical engineering and thermodynamics, particularly in the analysis of vapor-liquid equilibria.