Intermolecular Bonds

Question 1

what can

Answer 1

– Can be used as indicators of the strengths of intermolecular forces.

Answer 2

– The boiling point is the temperature at which the average kinetic energy
of molecular motion balances the attractive energy of intermolecular
attractions.

Answer 3

– When the pressure is 1.013 x 105 Pa, that temperature is the normal
boiling point.

Answer 4

– The conversion of a liquid into a gas is called vaporisation

Answer 5

– Condensation is the reverse process.

Answer 6

At temperatures below the freezing point, the molecules become locked in place and the liquid solidifies.
When the pressure is 1.013 x 105 Pa, that temperature is the normal freezing point.

Question 7

three types of intermolecular forces

Answer 7

dispersion forces
dipole-induced dipole forces
dipole-dipole forces

Question 8

1. Dispersion forces:

Answer 8

The attractions between the negatively charged electron clouds & the positively charged nuclei of neighbouring molecules. All substances display dispersion forces.

Question 9

2. Dipole-induced dipole forces:

Answer 9

– A molecule with a permanent dipole induces a dipole in a neighbouring
molecule.

Question 10

3. Dipole-dipole forces:

Answer 10

– Attractions between negatively charged end of a polar molecule &
positively charged end of another molecule (special case: hydrogen bond).

Answer 11

A hydrogen bond is a special type of dipole-dipole interaction

Answer 12

We know that if the positive end of one dipole interacts with the negative end of another dipole this is a dipole-dipole interaction

Answer 13

However, if the positive end of one dipole has a hydrogen covalent bond to either a N, O or F atom and the
negative end (of the second molecule) is either N, O or F atom then this interaction is a hydrogen bond

Answer 14

If the positive end of one dipole has a hydrogen covalent bond to either a N, O or F atom and the negative end (of the second molecule) is either N, O or F atom then this interaction is a hydrogen bond

Answer 15

A hydrogen bond is considered a strong intermolecular interaction, but it is much weaker than a O-H
covalent bond

Answer 16

In general, the stronger the
intermolecular forces, the higher the
melting and boiling points.

Answer 17

Please note, all molecules and
nonpolar atoms have dispersion
forces.

Answer 18

Molecules with a dipole will have
London Dispersion Forces and Dipole
-
Dipole Interactions

Answer 19

Molecules with a dipole and fulfill the
rules for hydrogen bonding have
London Dispersion Forces, Dipole
-
Dipole Interactions and Hydrogen
Bonding.

Question 20

solute

Answer 20

Solute: This is the substance that gets
dissolved. It can be a solid, liquid, or even a gas. Think of it as the “guest” in the mixture

Question 21

solvent

Answer 21

Solvent: This is the substance that does the dissolving. It’s usually present in a larger amount compared to the solute and acts as the “host” in the mixture, providing the medium for dissolving the solute.

Answer 22

In general hydrocarbons are non polar ———- London
dispersion Forces as a force of attraction between
molecules

Question 23

Polar Aprotic Solvents

Answer 24

In general compounds containing ketones (C=O) and ethers
(C-O-C) are polar ———- Dipole-Dipole interactions

Answer 25

From the electronegativity table C-O bond is polar covalent bond

Answer 26

Polar protic solvents tend to have high dielectric constants and high dipole moments.

Furthermore, since they possess O-H or N-H bonds, they can also participate in hydrogen bonding.

Question 27

Polar protic solvents

Answer 27

Methanol, Ethanol, Propanol ……
Cyclohexanol
Ethylamine, Aminopropane….. water

Question 28

Why do Molecular Substances Dissolve?

Answer 28

The more similar two compounds the more likely that one will be soluble in another

Answer 29

Polar compounds dissolve in Polar compounds and

Non-Polar compounds dissolve in Non-polar compounds

Question 30

An explanation why one substance will dissolve in another (Three steps)

Answer 30

1. Solute molecules are separated from each other.
   Solute–Solute attractions resist this.
2. Solvent molecules are separated from each other.
   Solvent–Solvent attractions resist this.
3. Solute and solvent molecules mix with each other.
   Solute–Solvent attractions assist this.

Question 31

explain enthalpy

Answer 31

Each one of these has a particular energy called (H) in this case it is
Heat energy (called Enthalpy) a change in heat energy is (triangle)H

Question 32

Molecular substances will dissolve in each other if:

Answer 32

1. H initial and H final are of similar energy H
2. Both solute–solute attractions and solvent–solvent attractions are weak so that there is little resistance to the
   tendency to mix
3. The solute–solvent attractions are sufficiently strong to overcome the
   resistance to mixing due to solute–solute and solvent–solvent attractions

Answer 33

The universe is moving towards greater disorder or larger Entropy
Applied to our system the solute and solvent has a natural tendency to mix
or move towards greater disorder

Answer 34

Entropy S is a measure of disorder

Answer 35

Energy systems have a tendency to increase their Entropy (S).

secondary law of thermodynamics

Question 36

miscible

Answer 37

The energy required to break the H-bonds between water molecules is compensated by the energy evolved in the formation of H-bonds between water and ethanol

Answer 38

The have form weak London dispersion forces between each other and begin with only
weak Hexane-Hexane and Octane-Octane dispersion forces

Question 39

why would two substances be immiscible

Answer 39

The hydrogen bonds in water prevent the mixing

The hexane-hexane interaction has only weak London dispersion force and overall the mixed system (if it
existed) would have far greater energy than the combined Hexane-Hexane and Water-Water systems

The hydrogen bonds prevent the system attaining greater disorder

Question 40

Alcohols have a polar end and a non polar end. This is an explanation as to why 1-propanol is miscible in both
Heptane and Water

Answer 41

As the non-polar end of any alcohol is increased so does its chances of being soluble in a nonpolar molecule. And less chance of being soluble in water

Answer 42

To understand if one liquid is miscible in another we need to
know the types of intermolecular forces present in each
molecule.

Question 43

requirements for isomer

Answer 43

must have same number of elements, e.g. octane isomers must have 8 carbon atoms and 18 hydrogen atoms