5. Complete Lewis diagrams and some physical properties for compounds X and Y are given. — VSEPR Theory, Intermolecular Forces, Vapor Pressure, Ideal Gas Law Chemistry Question
Problem Context
- Complete Lewis diagrams and some physical properties for compounds X and Y are given.
A. Based on VSEPR theory, predict the geometry around the Si atom in compound Y.
Model Answer
Tetrahedral [1].
B. A student claims that compound Y has a higher boiling point than that of compound X because compound Y has stronger London dispersion forces. Do you agree or disagree? Justify your answer.
Model Answer
Agree. Compound Y has a larger, more polarizable electron cloud
because the Si atom has more occupied electron shells than the C atom, giving
compound Y stronger London dispersion forces and a higher boiling point than
compound X [1].
C. An equimolar mixture of the two compounds is heated. When the mixture reaches 82°C, which compound will have the higher vapor pressure? Justify your answer.
Model Answer
Examples of acceptable responses may include the following:
* Compound X. Compound X has weaker intermolecular forces than compound Y, so
molecules of X are more likely to be in the gas phase at 82 °C and would
therefore have a higher vapor pressure [2].
* Compound X. At 82 °C, compound X has reached its boiling point, but compound
Y has not. Therefore, the proportion of X molecules in the vapor phase would be
much greater than that of compound Y, giving compound X the higher vapor
pressure [2].
D. The mixture is heated to 198°C in a sealed, rigid 12.5 L container, at which point both substances are gases and the total pressure in the container is 2.30 atm. Calculate the number of moles of gas particles in the container.
Model Answer
*PV* = *nRT*
*n* = *PV* / *RT* = (2.30 atm)(12.5 L) / (0.08206 L atm / K mol)(471 K) = 0.744
mol [3].
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