Chem - Ch 17/18 (Intermolecular forces & their affects/water)

Question 1

is solid water more or less dense than liquid

Answer 1

less

Question 2

solids have a(n) (definite/indefinite) shape and/or volume

Answer 2

definite

Question 3

liquids have a(n) (definite/indefinite) shape and/or volume

Answer 3

definite volume, indefinite shape

Question 4

When a molecule in a liquid state undergoes a phase change to a gas, it must what

Answer 4

break all the intermolecular forces acting upon it

Question 5

what four things are intermolecular forces related to

Answer 5

surface tension
vapor pressure
melting point
boiling point

Question 6

what are the 3 types of intermolecular forces

Answer 6

dispersion
dipole-dipole
Hydrogen bonding

Question 7

what three things affect boiling point

Answer 7

molar mass
polarity
intermolecular force

Question 8

what is the relationship (usually) between molar mass and boiling point

Answer 8

directly proportional

Question 9

what is the relationship between polarity and boiling point

Answer 9

directly proportional

Question 10

what is the relationship between IMFs and boiling point

Answer 10

stronger IMF, boiling point goes up

Question 11

why is solid water less dense than liquid water

Answer 11

the crystal structure of ice creates an open structure - a lot of empty space

Question 12

What factor causes the high surface tension, low vapor pressure, and high boiling point of water

Answer 12

The hydrogen bonding

Question 12

What factor causes the high surface tension, low vapor pressure, and high boiling point of water

Answer 12

The hydrogen bonding

Question 13

What is surface tension

Answer 13

The inward force that minimizes the surface area of a liquid

Question 14

Why does water always want to be in a sphere

Answer 14

Because of its high surface tension

A sphere is the smallest surface area for a given volume

Question 15

Why does a needle or a coin float on water

Answer 15

Bc surface tension forms a “net” because if the strong attractions (H bonds) between the water molecules

Question 16

How are temperature and kinetic energy related

Answer 16

Directly proportional

Question 17

How are the strength of the IMFs and the rate of vaporization related

Answer 17

The stronger the IMFs, the slower the rate of evaporation

Question 18

How can molecules escape from a liquid and become a vapor

Answer 18

they have to be on the surface (If it’s not boiling) and have enough kinetic energy

Question 19

What happens to the rate of evaporation as the temperature increases

Answer 19

There is a faster rate of evaporation because a greater number of molecules have enough kinetic energy to evaporate

Question 20

Evaporation is the opposite of what

Answer 20

Condensation

Question 21

What will happen in respect to evaporation and condensation in a closed container

Answer 21

At some point the rates of evaporation and condensation will be equal

Question 22

Why don’t the rates of evaporation and condensation ever equal out in an open container

Answer 22

The vapor molecules generally spread out faster than they can condense

Question 23

What us dynamic equilibrium

Answer 23

When the rate of evaporation equals the rate of condensation

Question 24

What us vapor pressure

Answer 24

The pressure exerted by the vapor when it is in dynamic equilibrium with its liquid

Question 25

What is the relationship between IMF and vapor pressure

Answer 25

The weaker the IMF, the more molecules will be in vapor, so higher vapor pressure

Question 26

Why does a weaker IMF mean higher vapor pressure

Answer 26

Because it's easier to break weak IMFs, so more molecules become a vapor, which means higher vapor pressure

Question 27

When there is a high vapor pressure, is it easier or harder for the liquid to evaporate

Answer 27

Easier

Question 28

Why/how is evaporation a cooling process

Answer 28

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

Question 29

Why do we sweat

Answer 29

To cool off - the warmer sweat drops leave our body, leaving behind cooler molecules, making us cooler

Question 30

What is heat of vaporization

Answer 30

The amount of heat energy required to vaporize one mole of the liquid

Question 31

What happens to the heat of vaporization as the polarity of a substance goes down/it has a weaker IMF

Answer 31

Heat of vaporization also goes down

Question 32

Why does the heat of vaporization decrease when polarity/strength of IMF decreases

Answer 32

Bc it takes less energy to vaporize something if the forces are weaker

Question 33

How are vapor pressure and temperature related

Answer 33

Directly proportional

Question 34

When does the boiling point occur

Answer 34

When vapor pressure is the same as the external pressure

Question 35

What is special about a boiling liquid

Answer 35

Molecules from anywhere in it, not just the surface, can vaporize

Question 36

What is the boiling point

Answer 36

The temperature required the have the vapor pressure equal the external pressure

Question 37

Why does water boil at a lower temperature on mt Everest

Answer 37

Because there is very low pressure there, so it requires less heat/energy to get the vapor pressure up to the external pressure

Question 38

What is another word for melting

Answer 38

Fusion

Question 39

What is heat of fusion

Answer 39

The amount of heat energy required to melt one mole of a solid

Question 40

Why is the heat of vaporization so much greater than the heat if fusion

Answer 40

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

Question 41

What is an equilibrium

Answer 41

Two states coexisting together

Question 42

What is the specific heat capacity

Answer 42

The amount of energy needed to raise the temperature of 1g of a substance by 1° C

Question 43

When water is at 0° C and 100° C what is the kinetic energy used for

Answer 43

To change the state of it, not raise them temperature

Question 44

What states of water exist at 0° C

Answer 44

Solid and liquid

Question 45

What states of water exist at 100° c

Answer 45

Liquid and gas

Question 46

What is the boiling point of water

Answer 46

100°C

Question 47

What is the freezing point of water

Answer 47

0°C

Question 48

What is the melting point of water

Answer 48

0°C

Question 49

The bonds between hydrogen and oxygen in a water molecule can be characterized as what

Answer 49

Intramolecular forces | Polar covalent bond

Question 50

When a water molecule forms a hydrogen bond with another water molecule, which atoms are involved in the interaction

Answer 50

A hydrogen from one molecule and an oxygen from the other molecule

Question 51

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

Answer 51

The dispersion forces between the helium molecules are less than the dispersion forces between the xenon molecules

Question 52

What process must exist in equilibrium with the evaporation process when a measurement of the vapor pressure is made

Answer 52

Condensation

Question 53

``` Put these forces in order of decreasing strength: Covalent bonds Dispersion forces Ionic bonds Hydrogen binds Dipole dipole forces ```

Answer 53

``` Ionic bonds Covalent bonds H bonds Dipole dipole Dispersion ```

Question 54

What types of elements make up molecular compounds

Answer 54

Non metals

Question 55

What types of elements make up atomic compounds

Answer 55

Noble gases

Question 56

What types of elements make up ionic compounds

Answer 56

A metal and nonmetal

Question 57

In terms of kinetic energy, explain how a molecule in a liquid evaporate

Answer 57

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

Question 58

Why does the boiling point of a liquid vary w atmospheric pressure

Answer 58

Bc in order for a liquid to boil, external pressure must equal vapor pressure

Question 59

When does boiling happen

Answer 59

When a liquid is heated to a temperature at which particles throughout the liquid have enough KE to evaporate

Question 60

Why is there no change in intramolecular forces when a solid is melted

Answer 60

Melting is a physical change, so the composition doesn't change, which means the intramolecular forces must stay the same

Question 61

Which is stronger: intermolecular forces or intramolecular forces

Answer 61

Intramolecular

Question 62

Which type of solid (ionic, molecular, or atomic) is most likely to have the highest melting pint

Answer 62

Ionic because ionic bonds are the the strongest force, so it takes more KE to loosen them

Question 63

Why does ammonia have a much higher boiling point than methane even though their molar masses are almost equal

Answer 63

Bc ammonia has H bonds so it takes more energy to overcome than dispersion forces which are present in methane

Question 64

Why does an alcohol rub on a person w a high fever cool them down

Answer 64

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.

Question 65

Why do an alcohol rub instead of a water rub

Answer 65

Alcohol evaporates easier than water bc there are no h-bonds holding the molecules together

Question 66

What is the relationship between vapor pressure and temperature

Answer 66

Directly proportional

Question 67

What is the relationship between kinetic energy and temperature

Answer 67

Directly proportional

Question 68

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?

Answer 68

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

Question 69

Why is the density of ice less than the density of water

Answer 69

The same mass occupies a larger volume

Question 70

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

Answer 70

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

Question 71

Two molecules are the same size, but one has H-bonding and the other has dispersion forces. Which has the higher boiling point

Answer 71

The one that can h-bond

Question 72

Two molecules have the same intermolecular forces, but one is much bigger. Which will have the higher boiling point

Answer 72

The bigger one

Question 73

On what factors does the heat capacity of an object depend

Answer 73

Mass and chemical composition