liquids, solids and intermolecular forces

Question 1

what is crystalline and amorphous solids

Answer 1

atoms or molecules that
compose them are arranged in a well-ordered three-dimensional array

atoms or molecules that compose them have no long range order

Question 2

low density of gaseous water is due to

Answer 2

the distance between each molecules is very large

Question 3

why is ice less dense than water

Answer 3

due to the unique crystal structure due to which the molecules move farther apart upon freezing

Question 4

why is the water molecules in liquid water able to move

Answer 4

freedom of movement is there even though the atoms and molecules in liquid are in close contact but the thermal energy partially overcomes this attraction

Question 5

why are protons and electrons attracted to each other

Answer 5

because when they come closer their potential energy decreases
the same goes for molecules with partial or temp charges

Question 6

what is the reason behind the relative weakness of intermolecular forces wrto bonding forces

Answer 6

it is due to Coulomb law
Bonding forces are the result of large charges (the charges on protons and electrons) interacting at very close distances.
Intermolecular forces are the result of smaller charges interacting at greater distances.

Question 6

which is the force present between all atoms and molecules and what causes it

Answer 6

dispersion force or London forces
it is caused by fluctuations in the electron distribution in atoms or molecules that is due to an instantaneous dipole or temporary dipole

Question 7

on what does the magnitude of dispersion force depend on

Answer 7

it depends on how easily the electrons in an atom or molecule move or polarize in response to an instantaneous dipole which in turn depends on the size of the electron cloud

Question 7

why does a large electron cloud result in larger dispersion force

Answer 7

the electrons are not held tightly by the nucleus hence the electrons can moves more freely
dispersion force increases with increase in molar mass

Question 7

dipole-dipole force s caused by

Answer 7

exists between all polar molecules
polar molecules have electron-rich region(-vely charge) and electron deficit region as seen in acetone which has a permanent dipole

Question 8

miscibility depends on

Answer 8

polarity of the compounds or molecules

Question 8

why does polar molecules have higher bp amd mp than non polar molecules

Answer 8

this is due to the presence of dispersion forces with the dipole-dipole forces this additional attractive forces rises mp and bp

Question 8

what is miscibility

Answer 8

the ability to mix without separating into 2 states – of liquids

Question 8

bp increases with

Answer 8

increase in dipole moment

Question 9

what is the electronegativity of carbon oxygen and hydrogen? and chlorine

Answer 9

c-2.5
o-3.5
H-2.1
Cl-3

Question 10

why is co2 molecule non polar

Answer 10

their structure is linear hence dipoles of polar bonds cancel each other out hence no dipole-dipole forces

Question 11

hydrogen(super dipole-dipole force) bond is seen in

Answer 11

polar molecules containing hydrogen bonded directly with smaller electronegative atoms like fluorine, nitrogen, or oxygen these show hydrogen bonding

Question 12

a hydrogen bond is caused by

Answer 12

The large electronegativity
difference between hydrogen and any of these electronegative elements causes the hydrogen atom to have a fairly large partial positive charge (d+) within the bond, while the F, O, or N atom has a fairly large partial negative charge (d-). In addition, since these atoms are all quite small, the H atom on one molecule can approach the F, O, or N atom on an adjacent molecule very closely. The result is a strong attraction between the H atom on one molecule and the F, O, or N on its neighbor—an attraction called a hydrogen bond

Question 13

state of ethanol and dimethyl ether in room temp

Answer 13

ethanol-liquid
dimethyl ether-gas

Question 14

what is ion-dipole force

Answer 14

occurs when an ionic compound is mixed with a polar compound
eg aqueous soln of ionic compounds

Question 15

what is surface tension

Answer 15

The surface tension of a liquid is the
energy required to increase the surface area by a unit amount. For example, at room temperature, water has a surface tension of 72.8 mJ>m2; it takes 72.8 mJ to increase the surface area of water by one square meter

Question 15

surface tension decreases with

Answer 15

decrease in intermolecular forces
paper clip cannot float on benzene bcs it only has dispersion forces

Question 16

what is viscosity

Answer 16

it is the ability of a liquid to resist flow

Question 17

what are the factors affecting viscosity

Answer 17

1-intermolecular forces stronger the force more viscous the liquid
2-size and shape of molecules large molecules cant move easily hence resist flow
3-temperature - ke increases less viscosity
KE decreases viscosity increases

Question 17

what is cohesive force

Answer 17

intermolecular force between molecules of a liquid

Question 18

what is adhesive force

Answer 18

interaction between molecules of a liquid and solid surface ability of liquid to adhere to the surface

Question 19

why does liquid form spherical shape when it comes in contact with non polar surface

Answer 19

bcs cohesive force>adhesive force and spherical droplets maximise hydrogen bonding

Question 20

what is the full form of SAE

Answer 20

society of Automotive engineers The thinnest motor oils have SAE ratings of 5 or 10, whereas the thickest have SAE ratings of up to 50

Question 21

what is capillary action

Answer 21

the ability of a liquid to flow against gravity up a narrow tube

Question 22

give the reason for concave meniscus in water and convex meniscus in mercury

Answer 22

concave meniscus-adhesive force>cohesive force convex meniscus-adhesive force

Question 23

what is vaporization

Answer 23

the process by which thermal energy can overcome intermolecular forces and produce a state change from liquid to gas

Question 23

what are volatile and non-volatile and give an example for each

Answer 23

volatile are compounds that vaporize very easily eg-acetone non-volatile are substances that does not vaporize very easily eg-motor oil 10w-40

Question 24

Summarizing the Process of Vaporization:

Answer 24

■ The rate of vaporization increases with increasing temperature. ■ The rate of vaporization increases with increasing surface area. ■ The rate of vaporization increases with decreasing strength of intermolecular forces.

Question 24

condensation is a

Answer 24

exothermic process

Question 25

vaporization is a

Answer 25

endothermic process vaporization requires overcoming the intermolecular forces that hold liquids together. Since energy is needed to pull the molecules away from one another, the process is endothermic

Question 26

what is the enthalpy of vaporization (𝚫Hvap).

Answer 26

The amount of heat required to vaporize one mole of a liquid to gas H2O(l) + H2O(g) ∆Hvap = +40.7 kJ>mol The heat of vaporization is always positive because the process is endothermic

Question 27

dynamic equilibrium

Answer 27

rate of vaporization=rate of condensation

Question 28

what is the vapor pressure? and what does it depend on

Answer 28

The pressure of a gas in dynamic equilibrium with its liquid intermolecular forces present in the liquid and the temperature

Question 28

give example for a balanced system

Answer 28

A liquid in dynamic equilibrium with its vapor is a balanced system that tends to return to equilibrium if disturbed

Question 29

what is the vapor pressure of n-pentane at 25 degree celsius

Answer 29

510mmhg

Question 30

state le chateliers principle

Answer 30

When a system in dynamic equilibrium is disturbed, the system responds so as to minimize the disturbance and return to a state of equilibrium.

Question 31

temperature dependence of vapor pressure

Answer 31

When the temperature of liquid increases, its vapor pressure rises because the higher thermal energy increases the number of molecules that have enough energy to vaporize

Question 32

what is boiling point

Answer 32

it is the temperature at which the vapor pressure of a liquid is equal to the external pressure When a liquid reaches its boiling point, the thermal energy is enough for molecules in the interior of the liquid (not just those at the surface) to break free of their neighbors and enter the gas state

Question 33

what is normal boiling point

Answer 33

the temperature at which its vapor pressure equals 1 atm

Question 34

what is critical temperature

Answer 34

it is the temperature at which the meniscus between the liquid and gaseous n-pentane disappears, and the gas and liquid states commingle to form a supercritical fluid it is the temp at which this transition occurs the liquid cannot exist above this temp

Question 35

what is critical pressure

Answer 35

it is the pressure at which the transition occurs

Question 36

what is supercritical fluid

Answer 36

it is neither gas nor liquid but it exhibits both of its properties it acts as a good solvent used to extract caffeine from coffee beans without losing its flavour using supercritical carbondioxide

Question 37

WHAT is sublimation and how does it occur

Answer 37

Even though a block of ice is solid, the water molecules in the ice have thermal energy, which causes each one to vibrate about a fixed point The molecules with high enough thermal energy can break free from the ice surface and go directly into the gas state

Question 38

what is deposition

Answer 38

Some of the water molecules in the gas state (those at the low end of the energy distribution curve for the gaseous molecules) collide with the surface of the ice and are captured by the intermolecular forces with other molecules. This process—the opposite of sublimation—is deposition

Question 39

name a substance that does not melt but only sublimes

Answer 39

dry ice or solid carbondioxide

Question 40

what is melting or fusion

Answer 40

The increasing thermal energy causes the water molecules to vibrate faster and faster. At the melting point (0 °C for water), the molecules have enough thermal energy to overcome the intermolecular forces that hold the molecules at their stationary points, and the solid turns into a liquid

Question 41

melting is

Answer 41

endothermic process the melting ice absorbs heat from the liquid

Question 42

what is heat of fusion(𝚫Hfus)

Answer 42

it is the energy required to melt 1 mol of a solid H2O(s) ¡ H2O(l) ∆Hfus = 6.02 kJ>mol

Question 43

freezing is

Answer 43

exothermic process

Question 44

what is enthalpy of sublimation

Answer 44

it is the energy required to sublime 1 mole of solid into gas

Question 45

what does y axis and x axis represent in heating curve

Answer 45

y axis - temp of water sample x axis- amount of heat added

Question 46

what does regions in a phase diagram represent

Answer 46

Each of the three main regions—solid, liquid, and gas—in the phase diagram represents conditions under which that particular state is stable

Question 47

what does x axis and y axis represent in a phase diagram

Answer 47

x axis-temperature y axis-pressure in torr

Question 48

what does lines in a phase diagram represent

Answer 48

Each of the lines (or curves) in the phase diagram represents a set of temperatures and pressures at which the substance is in equilibrium between the two states on either side of the line

Question 49

what does triple point in a phase diagram represent

Answer 49

The triple point in a phase diagram represents the unique set of conditions at which the three states are equally stable and in equilibrium. In the phase diagram for water, the triple point occurs at 0.0098 °C and 4.58 torr.

Question 50

what doe critical point in a phase diagram represent

Answer 50

the critical temperature and pressure, the liquid and gas states coalesce into a supercritical fluid. The critical point in a phase diagram represents the temperature and pressure above which a supercritical fluid exists

Question 51

Carbon dioxide forms a liquid only

Answer 51

above pressure of 5.1 atm