Chemistry Help - REDOX Reactions

in the equation, you are given the charges of each ion.

therefore you can see that in the equation, Fe becomes Fe^2+, and that 2H^+ becomes H2.

you can separate the changes in each element to give the two half-equations

Fe → Fe^2+ and 2H^+ → H2.

however, you can also show reduction and oxidation as gain and loss of electrons respectively (OILRIG: oxidation is loss, reduction is gain)

the symbol for electrons is e^-, and the number of electrons is shown by putting a number before this symbol (e.g. 2e^- is 2 electrons).

if an element gains electrons, then the added electrons are put on the left-hand side of the half-equation. this shows that at first, the electrons were separate from the element, but then became part of it.

gain of electrons will decrease the charge - it can make a neutral atom into a negative ion, and can make a positive ion into a neutral atom.

here, 2 positive hydrogen (2H^+) ions become a diatomic neutral hydrogen (H2) element.

when 2 electrons are added to the 2H+ ions, the two ions become H2. this gives the half-equation 2H^+ + 2e^- → H2.


if an element loses electrons, then the electrons lost are put on the right-hand side of the half-equation, since at first, the electrons were part of the element, but then became separate from it.

loss of electrons will increase the charge - it can make a neutral atom into a positive ion, and can make a negative ion into a neutral atom.

here, 1 iron(II) (Fe) atom becomes a positive iron ion (Fe^2+).

when the iron atom loses 2 electrons, it becomes an Fe^2+ ion with 2 electrons detached from it. this gives the half-equation Fe → Fe^2+ + 2e^-

Thank you so much! Could you help me with this one too?
Zinc chloride → zinc + chlorine

I'm not the same guy, but hopefully this helps regardless!

So the first things to work out are the formulae you need.

Zinc usually only forms a 2+ ion, and chloride ions have a -1 charge, so zinc chloride is ZnCl2.
Zinc metal exists on its own as a solid, and chlorine is a diatomic molecule of gas under standard conditions.

So your full equation is:

ZnCl2(s) → Zn(s) + Cl2(g)

Working out the oxidation numbers next:
In zinc chloride, zinc is a 2+ ion, so its oxidation number is +2. Chloride is a 1- ion, so its oxidation number is -1. Since zinc and chlorine are both elements, their oxidation numbers are both 0.

So the oxidation numbers change as follows:
Zinc: +2 → 0, so zinc is being reduced.
Chlorine: -1 → 0, so chlorine is being oxidised.

Using the OIL RIG mnemonic (oxidation is loss of electrons, reduction is gain of electrons), we can quite easily now write a pair of half equations.

Chlorine loses 1 electron: 2Cl^- → Cl2 + 2e^-
Zinc gains 2 electrons: Zn^2+ +2e^- → Zn

So to summarise:

Full equation: ZnCl2(s) → Zn(s) + Cl2(g)

Half-equations: 2Cl^- → Cl2 + 2e^- AND Zn^2+ +2e^- → Zn