A level Chemistry Q&A revsion

Just got the idea from another thread but this is for A level chem.
It does not matter which exam board at all.
let me start: Explain how London forces(ID-D or Van der waals forces) Arise?

Something to do with the movement of electrons in the atoms I think

Its a non-polar molecule, so there is a temporary dipole across the molecule causing one to become delta positive and the other delta negative..?

You ask a different question after you answered one so its like a chain reaction I guess. Let me start this off again: Define disproportionation reaction.

A reaction in which a compound is oxidised and reduced simultaneously.
For example the reaction of chlorine with water.

Q: What are the 2 conditions necessary for a dynamic equilibrium?

Forward and backward reaction must be same, concentration of Reactants and products stay constant

Q: Describe the formation of a pi-bond

1 electron from each of the two carbons overlaps, and forms an area of high electron density (electrons from p orbital) -- not sure if this is correct.

Q: What effect does a catalyst have on an equilibrium?

No effect but will speed up rate at which equilibrium is reached

Qefine standard enthalpy change of combustion

For you answer, just make sure you put that "both rate forward and backward reaction are increased EQUALLY", as I've seen in a past mark scheme that you must use the word equally for a mark.

The enthalpy change when 1 mole of a compound is burned completely in oxygen, under standard conditions, all substances in standard states.

Q: Why does the Maxwell-Boltzmann diagram/graph start at the origin?

For you answer, just make sure you put that "both rate forward and backward reaction are increased EQUALLY", as I've seen in a past mark scheme that you must use the word equally for a mark.

The enthalpy change when 1 mole of a compound is burned completely in oxygen, under standard conditions, all substances in standard states.

Q: Why does the Maxwell-Boltzmann diagram/graph start at the origin?

Because all molecules have energy, there are none without any energy

Q: Conditions for stereoisomers

Not possible for a particle to have 0 ke (csn easily be explained by heisenberg uncertainty principle/zero point energy) so therefore 0 particles have 0 ke. Since no one answered it before, explain how london forces arise.

Not possible for a particle to have 0 ke (csn easily be explained by heisenberg uncertainty principle/zero point energy) so therefore 0 particles have 0 ke. Since no one answered it before, explain how london forces arise.

When a molcules of high electron density approaches a non polar molecule, it induces the formation of a temporary dipole S+ and S- (not sure if completely correct)

What is a racemic mixture ?

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Its a bit more complex than that - london forces occur between neutral molecules. Although a molecule is neutral, the electrons within the molecule are moving randomly so instantaneously you might have more electrons on one side than the other so you get an instantaneous dipole. This induces a dipole in other nearby molecules, as the electrons are slightly more attracted to the positive end of the molecule, and fron there they will fluctuate in sync. A racemic mixture is one which contains equal amounts of each enantiomer so has no net rotation on plane polarised light, usually formed in sn1 reactions (as planar intermediate) or some reactions with carbonyl group as that carbon often has planar geometry around it so can be attwcked from above or below the plane of the molecule.

Explain the meaning of chemical shift in nmr

Ahh thank you!!

It is the amount of absorbance of energy at a certain frequency by a hydrogen environment relative to TMS and which depends on the number of shielding electrons and the presence of a highly electronagative molecule attached to the same carbon as Oxygen

Define a complex ion

You're almost there with chemical shift but not quite. Hydrogen atoms in nmr are effectively acting as magnets. In a magnetic field, the hydrogen atoms will align with the field. If you provide them with just the right amount of energy, provided by radiowaves, you can make them flip back and forth between being aligned and oppised to the field, which is known as resonance. In nmr, we typically use a fixed frequency of radiowaves and we measure the strength of the magnetic field required for resonance to occur. We use tms as a 0 point because it produces a very strong peak and the electrons are very close to the the hydrogen, so in practical terms (with sone weird exceptions) the hydrogens are most shielded so require the strongest magnetic field to resonate. We then measure the magnetic field strength of the compound and express its chemical shift in ppm - a chemical shift of 2 ppm means the field required to get resonance is 2 millionths less of the field required for tms. A complex ion is a metal ion surrounded by ligands which are bonded to the metal ion via dative covalent bonds. Explain what happens to the pH of water at different temps

Ah thank you so much, It's now much cleared than before!!!

H₂O ⇌ H⁺ + OH^-

The forward reaction is endothermic since it involves the breaking of bonds, when we increase the temperature then the forward reaction is favoured and more H⁺and OH^- will be produced so the pH of water will fall but it will stay neutral because the concentration of hydrogen ions will still equal the concentration of hydroxide ion. K_w will increase (K_w= [ H⁺ ] [ OH^- ] ) as more oh hydrogen and hydroxide ions are produced

Why an isomer is produced when the nitration of benzene occurs ?

Yep, there's also a nice maths way of doing it where you say [oh-]=[h+] so [h+] = rootkw and then sub into pH equation. You get multiple substitutions so you typically either get 1,3 or 1,5- dinitrobenzene. Describe the difference in base and acid hydrolysis of esters