Intermolecular Forces

Question 1

What determines stater of matter

Answer 1

Distance between particles

Question 2

What is the condensed phase?

Answer 2

Liquids and gases

Question 3

What happens when pressure is increased

Answer 3

Liquification/solidification

Question 4

What happens during phase change?

Answer 4

Heat increases the kinetic energy of the particles until the phase change occurs. During this part of the graph, KE remains constant and the heat increased the potential energy as the heat is used to pull apart the molecules

Question 5

What is deposition

Answer 5

Gas to liquid

Question 6

What is heat of fusion and heat of vaporisation?

Answer 6

Energy needed during melting from solid to liquid

Energy at boiling point that is required to convert a liquid to a gas

Question 7

What is polarisability?

Answer 7

Tendency of an electron cloud to distort. Increasing this increases LDF

Question 8

What does polarity affect?

Answer 8

MP, BP, solubility and chemical reactivity

Question 9

What must features must polarity have?

Answer 9

Have at least 1 polar bond and must NOT be symmetrical (C surrounded by 4 Cl-

Question 10

How does increased Mr affect LDF?

Answer 10

A larger molecule has more electrons thus the size of the induced dipole will be larger because there is greater polarisability and they can have greater fluctuations

Electrons are further away from the nucleus meaning they can move around easier and are more likely to from instantaneous/induced dipoles

Question 11

How does surface area affect LDF

Answer 11

Lower surface area eg linear molecules have stronger LDFs as there are greater chances for interactions

Question 12

What factors affect dipole-dipole interactions?

Answer 12

Increased polarity increased the interactions causing an increased BP

They are stronger than LDF if the polar molecules have similar size

Question 13

What is change in electronegativity

Answer 13

Different between the electronegativity of the two atoms in the molecule

Question 14

What causes LDF

Answer 14

Interactions between instantaneous and induced dipoles

Question 15

How do LDFs take place?

Answer 15

Occasionally an excess of electrons will accumulate one side of the atom/side and a shortage on the other causing an instantaneous dipole.
These electrons will repel those of another atom causing the same and resulting in an induced dipole

Question 16

What is the ion-dipole interaction?

Answer 16

Jon’s interacting with a partial charge in a polar molecule eg. Salt dissolving in water

Question 17

What is hydrogen bonding?

Answer 17

Hydrogen atom interacts with an unshared electron pair on and F, N and O that are small and very electronegative

Question 18

Explain the trend in H bonding

Answer 18

F—-H > H—-O > H——-N

Fluorine is the MOST electronegative and the HF bond is the most polar and strong BUT HF has only two lone pairs but only 1 Hydrogen.
Oxygen has 2 lone pairs and 2 hydrogens so it can make more H bonds than HN
N has only 1 lone pair, therefore not enough H

Boiling point of H20 is higher than HF

Question 19

How does H bonding take place?

Answer 19

Hydrogen ‘gives away’ it’s electrons to the other atom exposing its nucleus and allowing it to interact with a lone pair

Question 20

Why is ice denser than water?

Answer 20

I’ve has an open lattice structure as oxygen can bind 4 hydrogen atoms therefore it is less dense that H20

Question 21

What is vapour pressure?

Answer 21

The pressure exhorted by a vapour that is in equilibrium with its solid or liquid phases eg. Liquid molecules evaporate at the same rate that the vapour is condensing

Question 22

What affects VP?

Answer 22

Temperature due to increase KE of liquid molecules escaping as vapour

Question 23

Tell me about volatile liquids?

Answer 23

They evaporate easily and have a high VP

Question 24

What is boiling point?

Answer 24

Temperature when vapour pressure = atm pressure therefore it changes at different altitudes