Chem 102 HW (1)

24 July 2022
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question
Describe the relationship between the state of a substance, its temperature, and the strength of the intermolecular forces.
answer
Gas - weak Liquid - moderate Solid - strong
question
Why are intermolecular forces generally much weaker than bonding forces?
answer
Intermolecular forces are the result of smaller charges acting at greater distances whereas bonding forces are the result of larger charges acting at closer distances.
question
What is dispersion force?
answer
The result of fluctuations in the electron distribution within molecules or atoms. Present in ALL molecules and atoms.
question
What does the magnitude of the dispersion force depend on?
answer
The magnitude of the dispersion force depends on how easily the electrons in the atom or molecule can move or polarize in response to an instantaneous dipole, which in turn depends on the size of the electron cloud. A larger electron cloud results in a larger dispersion force.
question
How can you predict the magnitude of the dispersion force for closely related elements or compounds?
answer
Molar mass, molecular shape, and boiling points can predict magnitude.
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What is surface tension?
answer
The energy required to increase the surface area by a unit amount. - liquids tend to minimize their surface area.
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How does surface tension result from intermolecular forces?
answer
Interactions between molecules lower their potential energy. The molecules in the middle of the liquid have less PE than the molecules at the surface, so need energy to get to the surface.
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How is surface tension related to the strength of intermolecular forces?
answer
Surface tension decreases as intermolecular forces decrease.
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What is capillary action?
answer
The ability of a liquid to flow against gravity up a narrow tube.
question
How does capillary action depend on the relative strengths of adhesive and cohesive forces?
answer
Cohesive forces cause the liquid to stay together, adhesive forces cause the liquid to spread out over the surface of the tube. If the adhesive forces are greater than the cohesive forces, the liquid goes up the tube.
question
Explain what happens to a substance when it is heated in a closed container to its critical temperature.
answer
At the critical point, the meniscus separating the liquid and gas disappears, and the fluid becomes supercritical- neither a liquid nor a gas.
question
How do the properties of water differ from those of most other substances?
answer
Low molar mass, yet liquid at room temperature. High boiling point.
question
What are bands?
answer
molecular orbitals
question
What is the difference between a conduction band a a valence band?
answer
Conduction band- unoccupied orbitals Valence band- occupied orbitals
question
What happens to these physical properties as the strength of intermolecular forces increases?
answer
Increase: Boiling Point, Melting Point, Viscosity, Surface Tension. Decrease: Vapor Pressure.