Question

Consider the following vapor pressure versus temperature plot for three different substances A, B, and C.

If the three substances are CH₄, SiH₄, and NH₃, match each curve to the correct substance.

Short answer

At any temperature, the plot tells us that substance A has a higher vapor pressure than substance B, with substance C having the lowest vapor pressure. Therefore, the substance which contains the weak intermolecular forces is A, and the substance which contains strong intermolecular forces is C.

The $–\mathrm{NH}$bond can form hydrogen-bonding interactions, whereas the others cannot. Substance C is ${\mathrm{NH}}_3$_.The other two are nonpolar compounds with only London dispersion forces. Because ${\mathrm{CH}}_4$is smaller than ${\mathrm{SiH}}_4$_{, ${\mathrm{CH}}_4$}will have weaker London dispersion forces and is substance A. Therefore, substance B is ${\mathrm{SiH}}_4$.

Step-by-step solution

Step 1:Vapor pressure

Vapor pressure is the pressure exerted by the vapor of a liquid when both are in equilibrium. It is the direct measure of the intermolecular forces present in a substance.

Temperature

Temperature is the measure of hotness or coldness expressed in terms of several scales, including Fahrenheit and Celsius. Temperature shows the direction in which heat energy will spontaneously flow, that is, from one with higher temperature to another body with lower temperature).

Explanation

At any temperature, the plot tells us that substance A has a higher vapor pressure than substance B, with substance C having the lowest vapor pressure. Therefore, the substance which contains the weak intermolecular forces is A, and the substance which contains strong intermolecular forces is C.

The $–\mathrm{NH}$ bond can form hydrogen-bonding interactions, whereas the others cannot. Substance C is ${\mathrm{NH}}_3$ _.The other two are nonpolar compounds with only London dispersion forces. Because ${\mathrm{CH}}_4$is smaller than ${\mathrm{SiH}}_4$ _,${\mathrm{CH}}_4$ will have weaker London dispersion forces and is substance A. Therefore, substance B is ${\mathrm{SiH}}_4$.