AQA CHEM2 ~ May 23rd 2012 ~ AS Chemistry

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Brillaint that does help alot but what if the question is like:
An element X in period 3 of the periodic table has the following succesive energies

first 577kjmol^-1
second 1820kjmol^-1
third 2740kjmol^-1
fourth 11600kjmol^-1

Deduce them identity of element x.
Would there be a way to know this or would you just have to know the group 3 first ionisation energy? Thanks :smile:

You don't need to know any IEs by heart, just look at the data.

So for this example by far the biggest jump is between 3rd and 4th, so it must be in group 3. The question told you it is in period 3, so looking at the periodic table find the element in group 3 in period 3 and you'll see it is aluminium.

Make sense?

Reply 541

alex7892

Yehhh that really helpss! Thats brilliant, just sorted me out another mark haha !
Will positive you tommorow when I have some! :L

Reply 542

RosieH7

Original post by MedicalMayhem

Do you need the standard conditions bit? As I thought it was just enthalpy change when one mole of a compound is formed from its elements in their standard states? :redface:

I know they're similar, but wasn't sure if I would get 2 or 3 for that...

i think it's one mark for the enthalpy change when 1 mole of a compound is formed in it's standard state
then one mark for: from it's constituant elements in their standard states
third for all under standard conditions.

Although if you were really stuck you could always check a past paper mark scheme to be on the safe side.

Reply 543

Hdizzle

Original post by 3.14Pie

So true, then come the abandoment of this thread and the starting of the " CHEM4 AQA CHEMISTRY" thread :')

exactly!

Reply 544

Luppy021

Chemistry definitions(x31):
All the ones I have at the moment, some can be simplified but I haven't got round to doing it yet

Enthalpy change: Measure of heat energy change given out or taken in when a chemical or physical change occurs at constant pressure.

Enthalpy of formation:The enthalpy of formation is when one mole of substance is formed from its constituent elements with all reactants and products in their standard states.

Enthalpy of combustions: The enthalpy of combustion is when one mole of substance is burned completely in oxygen with all reactants and products in their standard states.

Hess’ law: The enthalpy change for a reaction is the same, independent of the route taken from reactants to products.

Bond dissociation enthalpy: The enthalpy change required to break a covalent bond with all species in the gaseous state.

Mean bond enthalpy: Mean value of the bond dissociation enthalpy for a given type of bond taken from a range of compounds.

Collision theory: Most collisions between molecules and other particles do not lead to a reaction.
They either do not have enough energy or are in the wrong orientation.

Activation energy: The minimum energy required that a particle needs in order to react.

Catalyst: A substance that increases the rate of a chemical reaction but is not used up in that reaction, by providing a different pathway for that reaction to occur with lower activation energy.

Heterogeneous catalyst: The catalyst is in a different phase to the reactants.

Homogeneous catalyst: The catalyst is in the same phase to the reactants.

Le Chatelier’s principle: If a system in equilibrium is disturbed, the equilibrium will move in the direction that tends to reduce that disturbance.

Dynamic equilibrium: Where the rate of the forward reaction equals to that of the backward reaction while the concentrations of the reactants and products remain constant.

Oxidation: A reaction in which an atom or group of atoms loses electrons.

Reduction: A reaction in which an atom or group of atoms gains electrons.

Oxidising agent: A substance that donates electrons.

Reducing agent: A substance that accepts electrons.

Oxidation state: The charge on an atom of element.

Redox reaction: Reaction in which electrons are transferred from one species to another.

Disproportionation: The simultaneous oxidation and reduction of a particular atom.

Free radical: A chemical species with an unpaired electron.

Electrophile: An electron deficient species that is an electron pair acceptor.

Nucleophile: An ion or group of atoms with a negative charge or partially negative charge region and is an electron pair donor.

Bio-fuel: A fuel derived or produced from renewable biological sources.

Polymerisation: The joining together of monomers to from long chain polymers.

Addition: Combination in which two or molecules join together to form a single molecule.

Substitution: Replacement of one atom or group of atoms by another atom or group of atoms.

Fingerprint region: The area of an infrared spectrum below 1500cm^-1, it is caused by complex vibrations of the whole molecule and is unique to a particular molecule.

Geometrical isomerism: Compounds with the same molecular formula, but a different spatial orientation of atoms.

Addition polymerisation: The formation of a large polymer from monomers joining together.

Elimination: Loss of a small molecule from a large molecule.

(edited 11 years ago)

Reply 545

Tayberry

Whats the definition of molecular ion , saw it on a past paper ? Also hydrolysis as well

Reply 546

clownfish

Original post by Luppy021

Oxidising agent: A substance that donates electrons.

Reducing agent: A substance that accepts electrons.

Disproportionation: The simultaneous oxidation and reduction of a particular atom.

Couple of edits to these for you:

Oxidising agent and reducing agent are the wrong way around. The oxidising agent causes something to be oxidised, ie an oxidising agent takes electrons from something.

Also disproportionation: an atom cannot be both oxidised and reduced, it shols be a species or element that is oxidised or reduced.

:smile:

Reply 547

clownfish

Original post by Tayberry

Whats the definition of molecular ion , saw it on a past paper ? Also hydrolysis as well

Molecular ion - the ion produced in mass spectrometry when the whole molecule loses one electron (ie the m/z for the molecular ion equals the RMM of the compound)

Hydrolysis - the splitting of a molecule by water.

Reply 548

Sorro10

Original post by BoltonTOM

THANKS!

Reply 549

Sorro10

Original post by Tayberry

Whats the definition of molecular ion , saw it on a past paper ? Also hydrolysis as well

6. State the meaning of the term hydrolysis. (1)

- Splitting/breaking the C-X/bond(s) using/by (adding)/with water OR
- Splitting/breaking the molecule/substance/compound using/by (adding)/with water.

8. State the meaning of the term molecular ion. (1)

The molecular ion is:
- The molecule with one/an electron knocked off/lost OR
- The molecule with a (single) positive charge OR
- the ion with/it has the largest/highest/biggest m/z (value/ratio) OR
- the ion with/it has an m/z equal to the Mr

Page 27 Post #532

Reply 550

tomtom415

I'm resitting this, got 106 UMS the first time around. I need 75/120 in chem5 to get an A. Currently loving life, as after having done chem4, chem2 is so so easy!

Reply 551

rommy123

what mechanisms do we need to learn for this unit??
Thanks in advance

Reply 552

Sorro10

Original post by rommy123

what mechanisms do we need to learn for this unit??
Thanks in advance

- Free Radical Substitution
- Nucleophilic Substitution
- Elimination
- Electrophilic Addition

Reply 553

cuckoo99

Original post by rommy123

what mechanisms do we need to learn for this unit??
Thanks in advance

nucleophillic substitution, Elimination, Electrophilic Addition

Electrophilic Addition occurs in 2 ways, 1 with H-Br and H2SO4 and the other way which includes the polarisation of the Br-Br molecule.

Reply 554

berryripple

Don't know anything about the alcohols, urgh.

Reply 555

kpcofgs

Original post by clownfish

How do you know it's in group 3? Because the ionisation energies jumped from three to four? Or is there something I'm not seeing here?

Reply 556

ElMoro

Original post by kpcofgs

How do you know it's in group 3? Because the ionisation energies jumped from three to four? Or is there something I'm not seeing here?

Yes

Since a lot more energy was needed to remove the 4th electron, you must've gone down a shell from the other three. That means the atom had three electrons in is outer shell so it was in group 3

Reply 557

Mocking_bird

Original post by berryripple

Don't know anything about the alcohols, urgh.

You mean you've not been taught it or you just don't understand it?
If you need any help, feel free to ask :smile:

Reply 558

username890104

Original post by Mocking_bird

If you need any help, feel free to ask :smile:

This.

Reply 559

clownfish

Original post by kpcofgs

How do you know it's in group 3? Because the ionisation energies jumped from three to four? Or is there something I'm not seeing here?

Original post by ElMoro

Yes

Since a lot more energy was needed to remove the 4th electron, you must've gone down a shell from the other three. That means the atom had three electrons in is outer shell so it was in group 3