Question

The diagram below shows the ln(P${}_{vapour}$) vs. 1/T for four substances. The Clausius Clapeyron equation describes this relationship.
The Clausius-Clapeyron equation is :

$ln\left(P_{vapour}\right)=-\frac{\Delta H_{vapour}}{R}\left[\frac{1}{T}\right]+C$

According to the graph, at high temperatures, which substance has the greatest vapour pressure?

• A. W
• B. X
• C. Y
• D. Z

Answer 1

Answer: (D)

Z

At high temperatures, $lnP=-\frac{\Delta H}{R}\frac{1}{T}+C$

As $T\to \infty ,\frac{1}{T}\to 0\Rightarrow lnP\to C$

High vapour pressure at high temperatures implies a high value of C.

Z has the highest value of C.