[or_il]

Hello
How are you ?

Somebody can help me please to balance this reaction ?

H3O+  +  Cr2O7  ---> Cr  +  H2O


Thank you !

[Borek]

It can't be balanced the way you wrote it. You omitted charges, and they play an important role. Besides, this looks like a half reaction - that means it can't be balanced without adding electrons on one of the sides.

[Twigg]

@Borek, True, but textbooks give these problems all the time expecting you to insert hydrogen ions and/or hydroxide ions where appropriate.

1) Split the half reactions
2) balance each individually with coefficients of e-
3) multiply both equations by terms that make the e- coefficients equal their lowest common multiple
4) re-combine equations

The rest isn't hard.

[chronictonic]

This is interesting too;

Chromium ions exist in a hexhydrate form denoted

[Cr.(H2O)6]^(3+)

these ions are acidic and in constant equilibrium between the states

[Cr.(H2O)6]^(3+)  AND  [CrOH.(H2O)5]^(2+) + H3O^(+)

I know its not relevant but i found it interesting