I need help balancing these two half-reactions.

[Kitty-Nin]

I am supposed to give the two half reactions , then the net equation, for the following redox reaction:

H₂O₂ + I- ----> I₂ + H₂O


I had balanced these as:

2 I₂ + 2 electrons ----> 2 I-

H₂O₂ ----> H₂O + 2 electrons

For a net reaction of:

H₂O₂ + 2 I₂ ----> H₂O + 2 I-


I'm told this is wrong, but I can't see any other way to do it, and don't understand what I'm doing incorrectly. Please help!

[GrahamKemp]

You can't just add electrons willy nihly, you have to have justification.

In the hydrogen peroxide half equation, first balance the hydrogen with protons, and then balance the charge with electrons.

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 H2O2 + 2 H{+} + 2 e{-} = 2 H2O

In the iodide half reaction, reverse the order.

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2 I{-} = I2 + 2 e{-}

Combine so that the electrons cancel (just as is).

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H2O2 + 2 H{+} + 2 I{-} = I2 + 2 H2O