Analyze the Chapter 12 Essay

intermolecular forces
the attractive forces that exist between all molecules
thermal/kinetic energy and intermolecular forces
when thermal energy is high relatives to intermolecular forces, matter is gaseous. when thermal energy is low relative to intermolecular forces, matter is liquid or solid
dependent on how much the molecules are interacting, high in solid and liquid,
water density anomaly
liquid water is more dense than ice because molecules actually move father apart as they freeze, good for aquatic animals so that their habitats don’t freeze
gas and pressure
gas in highly compressible, can easily be manipulated with a change in external pressure
type of solid, atoms and molecules are arranged in a well ordered 3D model, but there are more gaps
We will write a custom essay sample on
Any topic specifically for you
For only $13.90/page
Order Now
no long range order
state changes occur when:
there is a change in temp or pressure, more pressure more solid
intermolecular bond
bonds between atoms in a single molecule, formed and broken in chemical reactions, determine geometry and polarity
intermolecular force
forces of attraction or repulsion between molecules, broken and formed with phase changes, determines shape and physical properties
**usually much weaker than bonding forces
**interactions of small charges at greater distances
where do intermolecular forces originate from?
from interactions between charges, partial charges, and temporary charges ON MOLECULES, much like bonding forces originate from charged particles in atoms
dispersion forces
attractive forces between molecules due to instantaneous or induced dipoles, result of fluctuation in the electron distribution of the atoms or the molecule
**all molecules have dispersion forces
dispersion force trends
increases with radial size– electrons are held less tightly and therefore better able to polarize
increases with an increase in molar mass–more electrons in the cloud
**higher dispersion force, higher boiling point
**long thin structures have higher bp’s than circular ones– molecules have more surface area to interact between
dipole dipole
attractive force between the positive end of one molecule and the negative end of another, occurs with large differences in electronegativity and permanent dipoles
**polar molecules on each other
ability for two molecules to mix without separating into two states of liquid, polar molecules miscible with polar, nonpolar miscible with nonpolar
hydrogen bonding
known as a super dipole force, high partial charges combining together, very strong–without them all water would be gaseous
criteria for hydrogen bonding:
donor: any species with a hydrogen atom covalently bonded to F,O, N
acceptor: any species with a lone electron pair on F,O, N
ion dipole
when an ionic compound mixes with a polar compound, results in an ionic solution STRONGEST FORCE
method to compare boiling points
identify special molecular forces- ion dipole
compare molar masses
compare forces of molecules w similar mass
surface tension
energy required to increase the surface area by one unit, molecules at the surface have a higher potential energy than those on the interior (fewer neighbors to bond with), it takes energy to max surface area (because you are making more molecules unstable) thus liquids tend to minimize surface area.
this tendency creates a skin at surface that resists penetration
** an increase in surface area is resisted by surface tension, for something to sink, a force of energy must overcome the surface tension
** surface tension increases with an increase in intermolecular forces– thus you can’t float a paper clip on benzene (bonds are significantly weaker than hydrogen bonds in water)
*reason for why rain drops form tiny spheres, they are minimizing surface area, but larger bodies of water are too much affected by the force of gravity
the resistance of liquid to flow, greater in substances with stronger intermolecular forces, molecules are held more tightly to each other and don’t flow around each other as freely
also increases with an increase in molar mass and length– molecules are longer and can therefore become entangled, this binds them together stronger and they can interact with one another in multiple areas
also depends on temp– as temp increases, forces can become weaker which can cause a decrease in viscosity
capillary action
ability for a liquid to flow up a narrow tube against gravity, results from a combination of adhesive and cohesive forces, occurs if the adhesive forces are greater than the cohesive forces– water molecules are attracted to the surface, they cohesive forces then pull the rest of the water molecules along that are not in direct contact with the tube, water rises up until force of gravity balances capillary action
**plants: molecules at top evaporate because they have higher potential energy, rest of molecules move up due to cohesive forces
process by which thermal energy can overcome intermolecular forces and produce a state change from liquid to gas, the higher the temperature the greater the average energy of collection of molecules, ENDOTHERMIC
factors that increase the rate of vaporization
temp- gives the molecules more kinetic energy they need to overcome the intermolecular forces so they can break free and evaporate
surface area- as surface area increases, molecules are held less tightly (they are at the surface-bonded to fewer molecules) thus more can escape to vaporization
strength of forces- weaker forces, increase in rate of vaporization *volatile liquids evaporate easier than nonvolatile liquids
process of sweating/ evaporation
ENDOTHERMIC when we sweat our skin becomes covered with liquid, when this liquid absorbs heat from the body and then evaporates, resulting in cooling, high humidity slows the rate of evaporation because the air already contains large amounts of water
EXOTHERMIC, when water condenses it releases heat energy, why coastal regions to not get cold at night– already so much water in the air and when it condenses it releases heat and prevents temp from dropping too low, as opposed to winter nights in a desert
heat or enthalpy of vaporization
amount to heat required to vaporize one mole of a liquid to a gas, always positive because the process is endothermic (system gains heat)
dynamic equilbrium
occurs within a closed system, water molecules that evaporate cannot escape into the atmosphere, some start condensing back into the liquid state– the rate of concentration starts to increases, but with a constant water temp the rate of evaporation remains the same, eventually the rate of vaporization and the rate of condensation will be equal
vapor pressure
the pressure of a gas in dynamic equilibrium with its liquid
**only dependent on intermolecular forces and temperature
weak forces more pressure, higher temp more pressure
*changes in volume cause the pressure to drop temporarily then restore to equilibrium
***gas molecules condense to liquid at the same rate liquid molecules vaporize to gas
boiling point
the temperature at which the liquids vapor pressure equals the external pressure, the bubbles in boiling water are pockets of gaseous water molecules that float to the surface and evaporate
normal boiling point
the temperature at which vapor pressure equals 1 atm/760 torr, at lower pressure water boils at lower temperatures
celcius to kelvin
add 273.15
critical point
deals with a substance of increasing temp in a closed system,
density of gas increases (because they cannot escape to atmosphere) density of liquid decreases, meniscus disappears for two states to combine and form supercritical fluid –that exhibits both properties
*critical temp- temp at which transition occurs
*critical pressure- pressure at which transition occurs
when molecules in the solid phase have enough energy to break free (those at high end of distribution curve) and go directly into the gas phase (even though the temp is below the melting point), opposite can occur with molecules at low in of gas distribution curve– deposition
ex: even in airtight containers water can escape food and redepose on the inside of the bag, causing the food to be dehydrated
when thermal energy allows molecules to overcome the forces that hold them at stationary points, only weakens intermolecular forces, does not break them
heat of fusion
the amount of heat required to melt one mol of a solid, positive ENDOTHERMIC