CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Solid S is a white, non-conducting substance known to consist of discrete molecules held together by London dispersion forces. Its vapor pressure was measured over a range of temperatures and is tabulated below.
Temperature (°C)
Vapor pressure (torr)
0
1
10
3
20
8
30
20
40
45
50
90
60
180
70
320
80
550
The external atmospheric pressure at sea level is 760 torr, while on a certain mountain summit the atmospheric pressure averages 250 torr.
(a) Estimate the boiling point of solid S (that is, the temperature at which it will begin to boil rather than sublime) at sea-level pressure. Show your reasoning and any interpolations or extrapolations clearly.
(b) Using the same data set, estimate the boiling point of solid S on the mountain summit where the external pressure is 250 torr. Explain why this temperature differs from the sea-level value.
(c) A chemically similar substance T forms strong hydrogen bonds in the solid state. Predict qualitatively how the boiling point of T at 760 torr would compare with that of solid S, and justify your prediction.