Finding n

[Chisomaga Azu]

When finding the moles transferred in a half reaction, does the reaction have to be paired with another half reaction. For example, if we are given H2 --> 2H+ +2e-, would the electrons transferred be 2 or does the process change since there is no paired half reaction?

[806020644 3I]

I believe since you are still using electrons to balance the reaction, there is still a transfer of electrons from H2 to 2H+, even though there is no paired reaction.

[PranavKetharam]

In this instance, n would represent 2 electrons. A balanced half-reaction will have the same number of electrons for both the oxidation and reduction half-reactions. Thus, n=2 electrons even if you are given only one of the half-reactions.

[405963118]

unlike pv=nrt n does not equal moles. Here, in the half reacitons, n = the number of electrons. So if 2H+ has 2 electrons and it reacts with another reaction with 2 electrons on the opposite side, n = 2.

[Katie L 2I]

Half reactions do have to be paired with another reaction -- they can't occur on their own. But with your example with hydrogen, yes, n would be 2, corresponding to the 2 electrons, if it was the least common multiple between this half reaction and its paired one.

H+ --> H2 could be a reduction reaction in itself -- like Question 17 on the electrochemistry week 7/8 homework. But, if it's a half reaction, it should be paired.

[405981594]

That is only the half reaction so look at the coefficients on the balanced half reaction. In this case, it's 2 moles of electrons transferred for every 1 mole of H2 oxidized.

[806255289]

Within this half-reaction, 2 electrons are transferred per molecular of hydrogen gas. When considering just this half-reaction in isolation, it is not necessary to consider another half-reaction when determining the number of electrons transferred.

[Callista OConnor]

You would need to know the other half reaction as well. Because you cannot just assume that 2 e- will be transferred in the other half reaction as well-- in the overall redox reaction, you may have to multiple one or both half rxns by a coefficient in order for the # of transferred e- (n, essentially), to match.

For example, the other half rxn to this redox rxm may be transferring 5 e-. In that case, n would be 10, because that is the least common multiple of 2 and 5.

[andrea guzman 1F]

there is still a transfer of electrons in order to balance it so n=2.

[705903057]

In a half-reaction, the number of moles of electrons transferred is determined by the stoichiometry of the reaction. In the case you provided,
H2→2H++2e-, two moles of electrons are transferred for every mole of H2 consumed. This doesn't change regardless of whether the half-reaction is paired with another half-reaction or not. Each half-reaction represents the oxidation or reduction of a species, and the number of electrons transferred is determined solely by the stoichiometry of that specific half-reaction.