Redox Reactions/Half Equations...what on earth??

[futureless]

Hi, I'm studying Chemistry AS level and I was wondering if anyone could explain redox reactions and the whole method of getting half equations from whole equations and vice versa. I'd be really greatful if you could help, thanks people...

[Dr_Beula_PhD]

Redox reactions are reactions that involve the transfer of electrons between species.You have two reactions:oxidation and reduction,and these happen at the same time.

Oxidation involves loss of electrons while reduction is gain.Just think of O(xidation)I(s)L(oss)R(eduction)I(s)G(ain)!!!These two reactions are in "half equations".

For example:

Cu + Ag2+ + 2e = Cu2+ + 2Ag + 2e

 

so half equations would be

 

Cu = Cu2+ + 2e

 

Ag2+ + 2e = 2Ag

 

Hope that helps!!

[woelen]

The general idea behind this, is that half equations can be used to derive the full equations.

 

Half equations can be added to each other in any linear combination, but that must be done in such a way that the number of electrons at both sides is the same.

 

In the above example, there was an error, Ag is in oxidation state +1. This makes the example more interesting though.

 

Cu --> Cu(2+) + 2e

 

Ag(+) + e --> Ag

 

Now, we need to combine the equations. We can do that by adding one time the copper equation and two times the silver equation. In that way, we have equal numbers of electrons at both sides of the arrow.

[jdurg]

Also, the overall charge on the left hand side must equal the overall charge on the right hand side.

[woelen]

Also, the overall charge on the left hand side must equal the overall charge on the right hand side.

Yes, that is true, but if you start from correct half-equations and you add a linear combination of half-equations to each other, then you do not have to worry about charge balance, nor about a correct balance of elements. That 'automagically' will be correct, provided the half-equations are correct.

[Dr_Beula_PhD]

I do apologise for the error I made,my brains been overloaded the last couple of days!!