Chem - Ch 17/18 (Intermolecular forces & their affects/water) Flashcards
is solid water more or less dense than liquid
less
solids have a(n) (definite/indefinite) shape and/or volume
definite
liquids have a(n) (definite/indefinite) shape and/or volume
definite volume, indefinite shape
When a molecule in a liquid state undergoes a phase change to a gas, it must what
break all the intermolecular forces acting upon it
what four things are intermolecular forces related to
surface tension
vapor pressure
melting point
boiling point
what are the 3 types of intermolecular forces
dispersion
dipole-dipole
Hydrogen bonding
what three things affect boiling point
molar mass
polarity
intermolecular force
what is the relationship (usually) between molar mass and boiling point
directly proportional
what is the relationship between polarity and boiling point
directly proportional
what is the relationship between IMFs and boiling point
stronger IMF, boiling point goes up
why is solid water less dense than liquid water
the crystal structure of ice creates an open structure - a lot of empty space
What factor causes the high surface tension, low vapor pressure, and high boiling point of water
The hydrogen bonding
What factor causes the high surface tension, low vapor pressure, and high boiling point of water
The hydrogen bonding
What is surface tension
The inward force that minimizes the surface area of a liquid
Why does water always want to be in a sphere
Because of its high surface tension
A sphere is the smallest surface area for a given volume
Why does a needle or a coin float on water
Bc surface tension forms a “net” because if the strong attractions (H bonds) between the water molecules
How are temperature and kinetic energy related
Directly proportional
How are the strength of the IMFs and the rate of vaporization related
The stronger the IMFs, the slower the rate of evaporation
How can molecules escape from a liquid and become a vapor
they have to be on the surface (If it’s not boiling) and have enough kinetic energy
What happens to the rate of evaporation as the temperature increases
There is a faster rate of evaporation because a greater number of molecules have enough kinetic energy to evaporate
Evaporation is the opposite of what
Condensation
What will happen in respect to evaporation and condensation in a closed container
At some point the rates of evaporation and condensation will be equal
Why don’t the rates of evaporation and condensation ever equal out in an open container
The vapor molecules generally spread out faster than they can condense
What us dynamic equilibrium
When the rate of evaporation equals the rate of condensation
What us vapor pressure
The pressure exerted by the vapor when it is in dynamic equilibrium with its liquid
What is the relationship between IMF and vapor pressure
The weaker the IMF, the more molecules will be in vapor, so higher vapor pressure
Why does a weaker IMF mean higher vapor pressure
Because it’s easier to break weak IMFs, so more molecules become a vapor, which means higher vapor pressure
When there is a high vapor pressure, is it easier or harder for the liquid to evaporate
Easier
Why/how is evaporation a cooling process
When the high energy (warmer) molecules are lost from the liquid (bc they evaporate) it lowers the average kinetic energy. If energy is not drawn back into the liquid, it’s temp will decrease
Why do we sweat
To cool off - the warmer sweat drops leave our body, leaving behind cooler molecules, making us cooler
What is heat of vaporization
The amount of heat energy required to vaporize one mole of the liquid
What happens to the heat of vaporization as the polarity of a substance goes down/it has a weaker IMF
Heat of vaporization also goes down
Why does the heat of vaporization decrease when polarity/strength of IMF decreases
Bc it takes less energy to vaporize something if the forces are weaker
How are vapor pressure and temperature related
Directly proportional
When does the boiling point occur
When vapor pressure is the same as the external pressure
What is special about a boiling liquid
Molecules from anywhere in it, not just the surface, can vaporize
What is the boiling point
The temperature required the have the vapor pressure equal the external pressure
Why does water boil at a lower temperature on mt Everest
Because there is very low pressure there, so it requires less heat/energy to get the vapor pressure up to the external pressure
What is another word for melting
Fusion
What is heat of fusion
The amount of heat energy required to melt one mole of a solid
Why is the heat of vaporization so much greater than the heat if fusion
Because in order to vaporize something, you need to completely overcome the intermolecular forces and when you melt something, you only need to loosen the attractions
What is an equilibrium
Two states coexisting together
What is the specific heat capacity
The amount of energy needed to raise the temperature of 1g of a substance by 1° C
When water is at 0° C and 100° C what is the kinetic energy used for
To change the state of it, not raise them temperature
What states of water exist at 0° C
Solid and liquid
What states of water exist at 100° c
Liquid and gas
What is the boiling point of water
100°C
What is the freezing point of water
0°C
What is the melting point of water
0°C
The bonds between hydrogen and oxygen in a water molecule can be characterized as what
Intramolecular forces
Polar covalent bond
When a water molecule forms a hydrogen bond with another water molecule, which atoms are involved in the interaction
A hydrogen from one molecule and an oxygen from the other molecule
The freezing point of helium is approximately -270°C. The freezing point of Xenon is -112°C. What does this tell you about the IMFs in each molecule
The dispersion forces between the helium molecules are less than the dispersion forces between the xenon molecules
What process must exist in equilibrium with the evaporation process when a measurement of the vapor pressure is made
Condensation
Put these forces in order of decreasing strength: Covalent bonds Dispersion forces Ionic bonds Hydrogen binds Dipole dipole forces
Ionic bonds Covalent bonds H bonds Dipole dipole Dispersion
What types of elements make up molecular compounds
Non metals
What types of elements make up atomic compounds
Noble gases
What types of elements make up ionic compounds
A metal and nonmetal
In terms of kinetic energy, explain how a molecule in a liquid evaporate
Only molecules with a certain minimum amount of kinetic energy can evaporate. When a liquid is heated, the KE of the particles in creases, which gives the molecules the boost they need to overcome the attractive forces keeping them from evaporating
Why does the boiling point of a liquid vary w atmospheric pressure
Bc in order for a liquid to boil, external pressure must equal vapor pressure
When does boiling happen
When a liquid is heated to a temperature at which particles throughout the liquid have enough KE to evaporate
Why is there no change in intramolecular forces when a solid is melted
Melting is a physical change, so the composition doesn’t change, which means the intramolecular forces must stay the same
Which is stronger: intermolecular forces or intramolecular forces
Intramolecular
Which type of solid (ionic, molecular, or atomic) is most likely to have the highest melting pint
Ionic because ionic bonds are the the strongest force, so it takes more KE to loosen them
Why does ammonia have a much higher boiling point than methane even though their molar masses are almost equal
Bc ammonia has H bonds so it takes more energy to overcome than dispersion forces which are present in methane
Why does an alcohol rub on a person w a high fever cool them down
Alcohol evaporates really easily, and evaporation is a cooling process. As the particles w more kinetic energy, the hotter ones, evaporate, they leave behind the cooler ones.
Why do an alcohol rub instead of a water rub
Alcohol evaporates easier than water bc there are no h-bonds holding the molecules together
What is the relationship between vapor pressure and temperature
Directly proportional
What is the relationship between kinetic energy and temperature
Directly proportional
If heat is added to ice and liquid water in a closed container, and after the addition of the heat there is still ice and liquid water remaining, what happens to the vapor pressure and why?
The vapor pressure of the water will remain constant because the temperature stays constant (bc there is still water & ice) which means vapor pressure must also be constant bc VP and T are directly proportional
Why is the density of ice less than the density of water
The same mass occupies a larger volume
A 100g sample of water is heated from 50°c to 100° c. At 100°c, although heat is still being applied, the temperature does not rise. Explain why
100° C is the boiling point of water and also the point at which water vapor condenses. These two states, liquid and vapor, are in an equilibrium - they are coexisting together. At this temperature, the kinetic energy in the form of heat that is being applied is being used for the water to change states rather than to change the temperature of it
Two molecules are the same size, but one has H-bonding and the other has dispersion forces. Which has the higher boiling point
The one that can h-bond
Two molecules have the same intermolecular forces, but one is much bigger. Which will have the higher boiling point
The bigger one
On what factors does the heat capacity of an object depend
Mass and chemical composition
