Place the following substances in order of decreasing vapor pressure at a given temperature. PF5 BrF3 CF4 A) BrF3 > PF5 > CF4 B) BrF3 > CF4 > PF5 C) PF5 > BrF3 > CF4 D) CF4 > BrF3 > PF5 E) CF4 > PF5 > BrF3

A. BrF3 > PF5 > CF4

Explanation:

The vapor pressure of a gas is the number of times a given volume of the gas is as heavy as the same volume of hydrogen at a particular temperature and pressure.

The vapor pressure of a gas is related to its relative molecular mass as shown in the formulae:

Vapor pressure = 1/2 * relative molecular mass of the gas.

In the question therefore, calculate the relative molecular mass of each of the substance and divide by two, you will get the vapor pressure.

V. P (PF5) = 126/2 = 63

V. P (BrF3) = 136.9/2 = 68.45

V. P (CF4) = 88/2 = 44

In order of decreasing vapor pressure, BrF3 has high vapor pressure, followed by PF5 and then CF4.

BrF3 > PF5 > CF4