what is dispersion force
present in all molecules and atoms and increase with increasing molar mass; always weak in small molecules
why does having a larger electron cloud result in a greater dispersion force
because the electrons are held less tightly by the nucleus and therefore polarize easier
why do boiling points increase with increase strength of intermolecular forces
because more thermal energy is required to separate the particles from the liquid state into the gas state
what is dipole-dipole force
it exists in all molecules that are polar
has electron rich and electron deficient regions
what has higher melting and boiling points
polar molecules
what is miscibility
the ability to mix without separating into two states
what is a permanent dipole
molecules, such as acetone, are attracted to one another via dipole-dipole interactions
what is a hydrogen bond
strong attraction between the H atom and F, O, or N
what is the strongest intermolecular force that occurs in pure substances
hydrogen bonds
what is a ion-dipole force
occurs when an ionic compound is mixed with a polar compound; very strong with aqueous solutions
Pick the compound with the highest boiling point in each pair. Explain your reasoning
A) CH3OH or CH3SH
B) CH3OCH3 or CH3CH3COH
C) CH4 or CH3CH3
A) CH3OH - hydrogen bonding
B) CH3CH2OH- hydrogen bonding
C) CH3Ch3- bigger mass
In each pair of compounds, pick the one with the higher vapor pressure at a given temp
a) CH or CH3Cl
b) CH3CH2CH2OH or CH3OH
c)CH3OH or H2O
a) CH- smaller mass
b) CH3OH- smaller mass
c) H2CO - lacks hydrogen bonding
Which compound would you expect to have a greater surface tension: acetone or water. Explain
Water because surface tension increases with increasing intermolecular forces
Water in a glass tube that contains grease or oil residue displays a flat meniscus whereas water in a clean glass tube displays a concave meniscus. Explain
water experiences adhesive forces with glass that are stronger than its cohesive forces, causing it to climb the surface of a glass tube. water does not experience strong intermolecular forces with oil, so if the tube is coated in oil, the water's cohesive forces will be greater and it will not be attracted to the surface of the tube
which evaporates more quickly: 55 ml of water in a beaker with a diameter of 4.5 cm of 55 ml of water in a dish with a diameter of 12 cm
the water in the 12 cm dish will evaporate more quickley because the bigger the surface area, the more molecules to obtain enough energy at the surface and break free
which evaporates more quickly: 55 ml of water in a beaker or 55 ml of acetone in a beaker
acetone because it is more volatile than water and acetone has the higher vapor pressure bc it is lighter
how much energy is released when 65.8 g of water freezes
22 kj
an 8.5 g ice cube is placed into 225 g of water. Calculate the temp change in the water upon the complete melting of the ice
2.7 C
How much ice (in grams) would have to melt to lower the temp of 352 ml of water from 25 C to 5 C (assume the density of water is 1 g/ml) (heat of fusion is 6.02 kJ/mol)
87.99 grams
how much heat (in kj) is evolved in converting 1 mol of steam at 145 C to ice at -50 C. The heat capacity of steam is 2.01 J/g *C, and that of ice is 2.09 J/g*C (heat of fusion for steam is 2230, heat of fusion for water is 334, heat of fusion for ice is 6.02)
51.2 kj
what has the smallest surface area
sphere
what is viscosity
the resistance of a liquid to flow
where is viscosity greater in
substances with strong intermolecular forces because if molecules are more strongly attached to each other, they do not flow around each other as freely
what is capillary action
the ability of a liquid to flow against gravity up a narrow tube; like taking a blood sample
what is cohesive forces
the attraction between molecules in a liquid; cause the liquid to stay together
what is adhesive forces
the attraction between those molecules and the surface of the tube; causes liquids to spread out over the surface of the tube
what is vaporization
the process by which thermal energy can overcome intermolecular forces and produce a state change from a liquid to a gas
why does evaporation take faster than condensation
most of the newly evaporated molecules escape into the surrounding atmosphere and never come back
what increases the rate of vaporization
increasing temp
increasing surface area
decreasing strength of intermolecular forces
is motor oil volatile or nonvolatile
nonvolatile
is vaporization endothermic or exothermic process
endothermic
why do weak intermolecular forces result in volatile substances
because the intermolecular forces are easily overcome by thermal energy
what happens if the pressure increases in a liquid-vapor system
some of the vapor condenses, bringing the pressure back down to the equilibrium pressure
what is sublimation
the transition from solid to gas
what is deposition
the transition from gas to solid
why does sublimation occur at a greater rate than deposition
because of the most newly sublimed molecules escape into the surrounding atmosphere and never come back
is melting ice endothermic or exothermic
endothermic because it absorbs heat from the liquid
is freezing endothermic or exothermic
exothermic because heat is released
what takes less time: heat of vaporization or heat of fusion
heat of fusion
what is the triple point in a phase diagram
represents the unique set of conditions at which three states are equally stable and in equilibrium
what is unique about water
the solid form is less dense than its liquid form, which is why ice floats
water expands when it freezes