ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: kenhung123 on May 11, 2010, 11:32:24 pm

Title: Single or double arrow
Post by: kenhung123 on May 11, 2010, 11:32:24 pm

Is there anyway to know that a carboxylic acid requires single or double arrow when reacting with water?

How about in general? Because not all polyprotic substances are weak acids are they?

Title: Re: Single or double arrow
Post by: crayolé on May 12, 2010, 04:40:08 pm

I was under the impression that only H2SO4, HCl and HNO3 were the only acids that reacted fully, but thats with my limited knowledge from bludging all last year.

All carboxylic acids would probably be a double arrow since ethanol hardly ionises with water and I can't see it becoming any better as the chains get higher

Title: Re: Single or double arrow
Post by: Mao on May 12, 2010, 05:51:24 pm

All acid + base will have single arrows [reaction is complete]

All acid + water (Except for very strong acids, such as H2SO4 [1st ionisation only], HCl and HNO3) should have double arrows

Title: Re: Single or double arrow
Post by: m@tty on May 12, 2010, 06:33:41 pm

So is the double arrow required every time you write such a reaction?

Title: Re: Single or double arrow
Post by: kenhung123 on May 12, 2010, 07:58:59 pm

Quote from: m@tty on May 12, 2010, 06:33:41 pm

So is the double arrow required every time you write such a reaction?

I would assume so but its not often.

Btw, Mao that is very, very useful. Thanks a lot.

Title: Re: Single or double arrow
Post by: Mao on May 12, 2010, 09:28:44 pm

Single arrow usually mean complete reaction (or complete conversion). So if you know the reaction is rigorous and will only proceed forward (such as combustion, acid/base neutralization, ionisation of strong acid, etc), it will be single arrow. If you know the reaction does not reach completion under 'normal' circumstances (such as weak acid + water (partial ionisation), esterification, etc), it should have a double arrow.

Technically, all reactions should have a double arrow, you'll learn about this (dynamic equilibrium) next semester.