Help with balancing equation...?

Question

Can someone please help me balance this equation?

PH3 + I2 + H2O --> H3PO2 + HI

Answer 1

2PH3+4I2+4H2O -->2H3PO2+8HI

Answer 2

PH3 +2I2 +H2O --> H3PO2 +4HI

Answer 3

PH3 + 2I2 + 2H2O -> H3PO2 + 4HI

I goes from 0 to -1

P goes from -3 to +1

You need 4 I atoms per P atom.

Answer 4

The key to making sure that redox reactions are balanced is to insure that they are charge balanced as well as mass balanced.  Many redox reactions can be "balanced" by inspection, but they won't always be charge balanced.

The best way, that I've found, is to use the half-reaction method.

P is oxidized from -3 to +1, and I is reduced from 0 to -1.  Be sure the number of electrons "gained" equals the number "lost".

PH3 + 2H2O  -->  H3PO2 + 4H+ + 4e-

2(I2 + 2e-  --> 2I-)

--------------------------------------...

PH3 + 2I2 + 2H2O --> H3PO2 + 4H+ + 4I-

or, in molecular form

PH3 + 2I2 + 2H2O --> H3PO2 + 4HI