AS Chemistry- helping each other out!

How am I suppose to know that Ca(OH)2 (s) + NH4Cl (s) releases ammonia gas?

It's a question, but I don't understand why the answer is
NH4Cl (s) + Ca(OH)2 --> CaCl2 + 2NH3 (g) + H2O (g)?

Well if you react them together you're not going to get magnesium oxide are you?
Just think logically about if you compounds consist of various elements, what standard compounds could be formed as products




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Thanks that makes sense, unfortunately chemistry is not my forté

If you need help just holla
A2 Student atm with an A at AS
You do edexcel?


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I do OCR A, how did you manage to get an A at AS :O

Hellloooooo. Okay so I have my evaluative exam tomorrow on the enthalpy change of combustion (OCR A).

I am just doing some calculations and came across this Q (for those doing OCR A AS its p199 1b):

Given the following enthalpy changes of combustion C(s) = -394 kJmol, H2(g) = -286kJmol, C2H5OH(l) = -1367 kJmol

Determine the enthalpy change for:

2C(s) + 3H2(g) + 1/2O2(g) = C2H5OH(l).


So I followed the worked example but because I haven't been given the enthalpy change of combustion for oxygen, I had no idea how I was supposed to work out deltaH.

I did 2(-394) + 3(-286) + unknown enthalpy change of combustion for 1/2 O2 = delta H + -1367.

= -1646 + unknown enthalpy of combustion for 1/2 O2 - -1367

= -279 + 1/2 O2 = delta H.


The answer in the book is -279kJmol-1, but I don't understand! What happens with the oxygen? Doesn't it affect anything? I just can't get my head around it. Thank you to anyone that helps you may be the reason I don't fail tomorrow lol

I guess the reason why I love Amount of Substances is because I love Maths and for me Amount of Substances is the best way I can exercise my Maths skills in a different subject.

No you're not being nosy at all

I student Maths, Physics and of course Chemistry.

I dropped English Literature at AS because I knew I would've neglected putting effort into it until the end of the year, even though I loved the subject, I didn't want to put that kind of stress on myself as I knew deep down I will always prioritise Maths and Sciences.

Uh outside school hours I'd spend at least 4.5 hours a day in general for school work but most of the time I use that time to do Maths homework because my teacher gives my class a crap load to do everyday

I cannot give you an approx figure as to how many hours I spend for each subject because how I use my time depends on how much work I get given from my teachers and whether I'll have enough time after to do my own independent revision.

But I think its safe to say most of my weekend is revision and consolidating time.

I hope that helps.

Now I hope I'm not being nosy by asking what other A - Levels you do.

Okay, I just made two documents about Organic Chemistry, one to do with the uses of halogenoalkanes and the other relevant to the nucleophillic subsitution mechanisms you're expected to learn for AS

I've explained everything about nucleophillic substitution in the booklet including the mechanism for both alcohols and amines as well as an explanation behind each step for each mechanism. Hope it helps.

All the images I took were from either, chemguide.co.uk, chemrevise.org or masterorganicchemistry.com

Hope it helps

A rep would nice

Nice, thanks for making these

You're welcome

PM/VM me if you want anyone more revision resources for chemistry, I'm happy making them

As we're on different exam boards, I don't think some of the content will be relevant, but if I do need anything, I will definitely contact you!

Is it because oxygen is an element in its standard state therefore its standard enthalpy is 0? So it effectively doesn't count?

The enthalpy change of combustion is defined as: the enthalpy change that takes place when 1 mole of a substance reacts completely with oxygen under standard conditions.
It is expressed with the quantities:

If you look at the example on page 193, CuSO_{4 (aq)} is reacted with excess Magnesium. Again the figure for [delta]H is only the change for CuSO₄ not Mg!

I believe this is because the Carbon and Hydrogen, going back to your question, are the fuels that are reacted and oxygen just allows the reaction to happen. Also by definition the reacting substances must be 1 mole and in your reaction oxygen is not...

Sorry if I complicated things even more for you, but I hope this helped

Who wants the Edexcel Chemistry Controlled Assessment?

You think I dont have it?