CHM-10

Raoult's law

p_i = x_i p_i*. Partial pressure of an ideal-solution component.

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SolutionsRaoult 1887

Governing equation

p_i=x_i p_i^*

$x_i \in \left[0, 1\right]$

where

x_i: Mole fraction (—)
p_i^*: Pure vapour pressure (kPa)
p_i: Partial pressure (kPa)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

p_i=x_i p_i^*

$x_i \in \left[0, 1\right]$

$x_i = 0$ $p_i = 0$

Along the curve

②

Domain of the variable — blue

x_i_{\min} = 0,\quad x_i_{\max} = 1

$x_i \in \left[0, 1\right]$

$x_i = 0$ $x_i = 0$

Along the curve

③

Response curve — green

p_i=x_i p_i^*

$x_i \in \left[0, 1\right]$

$x_i = 0$ $p_i = 0$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}p_i}{\mathrm{d}x_i}

$x_i \in \left[0, 1\right]$

$x_i = 0.006$ $p_i^{\prime} = 12$

Along the curve

Lecture brief

Historical brief

Ideal-gas law, van ’t Hoff, Nernst, Michaelis–Menten and Clausius–Clapeyron are physical chemistry’s working equations of equilibrium and rate. The lab is pressure, potential and kinetics. This sheet (CHM-10 — Raoult's law) is the form associated with Raoult 1887. Working symbols: $x_i$ , $p_i^*$ $\rightarrow$ $p_i$ . The vapour mole fraction follows y_i p = x_i p_i*. Positive/negative deviations diagnose nonideality.

Purpose

Purpose: compute

p_i

from

x_i

p_i^*

in Physical chemistry via

p_i=x_i p_i^*

p_i = x_i p_i*. Partial pressure of an ideal-solution component. Use it when a real physical chemistry question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

x_i = 0.400\,\mathrm{—}

p_i^* = 12.000\,\mathrm{kPa}

, the governing relation

p_i=x_i p_i^*

yields

p_i = 4.800\,\mathrm{kPa}

. Binary ideal liquid, one volatile component shown. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Mole fraction x_i0.4 —Pure vapour pressure p_i^*12 kPa

Outputs

Partial pressure p_i4.800 kPa

Reading speed

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Narration of this film

Binary ideal liquid, one volatile component shown.

The vapour mole fraction follows y_i p = x_i p_i*. Positive/negative deviations diagnose nonideality.

Reading speed

Watch on YouTube