Another question on Kinetics:

1) Consider the following reaction: Zn(s) + 2HCl(aq) --> ZnCl₂(aq) + H₂(g)

Explain the effect, if any, on the rate of reaction of:

- (i) Increasing the pressure (2 marks)
- (ii) Adding water (2 marks)
- (iii) Using hydrobromic acid (HBr), on the same concentration, instead of hydrochloric acid.

For part

- (i) No effect as it is not in a gaseous state?
- (ii) Not sure
- (iii) Not sure ;p

Help pl0x

yup no effect 'cuz its not in gaseous state

i think it reduces because it dilutes the HCl further reducing the concentration of it, so there are less collisions between the reactants- HCl and the Zn

HBr is a stronger acid therefore rate of reaction will increase

Reply 185

cuckoo99

Original post by Hdizzle

indeed acids get stronger as you go down group 7 due to weaker bonding between H-X where X is a Halogen

Reply 186

mbisababe

could someone please explain how you would know what the temperature was before/after mixing on the extrapolation of the graph? i was looking through the june 09 paper and although you dont have the results, iw as completely stuck as to what you would actually do :frown:

Reply 187

longman240

I saw this and when it said 23rd May, my heart jumped, that gives me almost two weeks more than I originally thought. Thank you so much! I don't have any questions at the moment but I'd just like to thank you for that! :smile:

Reply 188

cuckoo99

Doing free radical substitution :smile:

pretty easy so far, just worried about how many mechanism's we have to learn :O

Reply 189

Hdizzle

Original post by cuckoo99

Doing free radical substitution :smile:

pretty easy so far, just worried about how many mechanism's we have to learn :O

4

the only one that i'm a bit dodgy with is that nucleophillic addition one
went over it so quickly in lesson :frown:

my revision guide needs to hurry up in the post!

i really want an A overall *sigh*

Reply 190

Mocking_bird

I enjoy the mechanisms so far.. they just seem routine to do.

Reply 191

samfreak

anyone got the gce aqa biology or chemistry unit 1 question paper for jan 2012? could you please upload it or send me it thanks ever so much

Reply 192

Natty.B

Original post by samfreak

anyone got the gce aqa biology or chemistry unit 1 question paper for jan 2012? could you please upload it or send me it thanks ever so much

i've only got the chem paper

AQA-CHEM1-QP-Jan12.pdf383.6KB

Reply 193

Sorro10

Original post by 3.14Pie

AH I might just start doing some topics at home, how exactly do you revise, your ums was amazing!

Note how many days left for exam,
clear desk of everything, print a syllabus,
start from point 1 topic 1, tick as you go along if you know it, bits you don't know makes notes on that from various sources (internet, books, school book etc.) then once you have completed every topic, go to aqa website, print off every past paper and mark scheme including specimin, and do the papers for the remaining time left, make a note on the front of the paper where you went wrong, then revise that and then move onto the next paper, and eventually you'll start to get 100%.

Gl :smile:

Reply 194

Sorro10

AQA CHEM2 January 2012 PAST PAPER on first page 1st post

Reply 195

Sorro10

Mechanisms

For AS-Chemistry there are 4 Mechanisms you need to know:

- Free Radical Substitution
- Nucleophilic Substitution
- Elimination
- Electrophilic Addiditon

i) Free Radical Substitution

STEP 1: Initiation --> Production of Free Radicals by homolitic fission

eg. Cl₂ --UV--> 2Cl·

STEP 2: Propagation --> The reaction of a Free Radical with a molecule to produce another free radical. [2 Steps]

eg. Cl· + H-CH₃ ------> HCl + ·CH₃
·CH₃ + Cl-Cl ------> CH₃Cl + Cl·

STEP 3: Termination --> Combination of 2 Free Radicals to produce a single molecule.

eg. Cl· + Cl· ------> Cl₂
·CH₃ + ·CH₃ ------> CH₃CH₃

(edited 12 years ago)

Reply 196

leofranco

Has anyone done the isa based on the unit 2 content. done the practical already - based on test tube observations - but wanted some help for what to look into for the written paper.