Question #fee47
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"What balanced equation represents a redox reaction?"
You balance an equation with parentheses the same way as with other equations.
You must remember to multiply the subscripts of atoms inside the parentheses by the subscripts outside the parentheses.
For example, balance the equation:
Fe(NO3)2+Na3PO4→Fe3(PO4)2+NaNO3
The standard method is to balance by inspection:
- First balance all atoms other than O and H.
- Then balance O.
- Then balance H.
Start with the most complicated formula. Here, it is Fe3(PO4)2:
We have three Fe atoms on the right, so we need to have three Fe atoms on the left hand side of the equation.
3Fe(NO3)2+Na3PO4→1Fe3(PO4)2+NaNO3
We have two P atoms on the right side (one P atom, which is inside the parentheses, is multiplied by the 2 outside). So we need two P atoms on the left hand side of the equation.
3Fe(NO3)2+2Na3PO4→1Fe3(PO4)2+NaNO3
Now we have six N atoms on the left hand side (1 N atom inside the parentheses is multiplied by the 2 outside and again by the 3 in front of the whole formula). We need six N atoms on the right hand side of the equation.
3Fe(NO3)2+2Na3PO4→1Fe3(PO4)2+6NaNO3
We have 6 Na atoms on the left and 6 Na atoms on the right, so Na is balanced.
Now we want to balance O atoms. The total number of O atoms on the left hand side of the equation is 26. So we have 8 + 18 = 26 O atoms on the right. O atoms are balanced.
The balanced equation is:
3Fe(NO3)2+2Na3PO4→Fe3(PO4)2+6NaNO3
We balance by inspection, but we treat each group inside parentheses as if it were a single atom.
This is sometimes called the "EASY" way.
For example, balance the equation:
Fe(NO3)2+Na3PO4→Fe3(PO4)2+NaNO3
The groups inside parentheses behave as a unit, so we treat the NO3 as if it were an atom X, and PO4 at if it were an atom Y.
Then the equation becomes
FeX2+Na3Y→Fe3Y2+NaX
We begin with Fe3Y2 and balance Fe.
3FeX2+Na3Y→1Fe3Y2+NaX
We have 2 Y groups on the right hand side, so we need 2 Y groups on the left hand side of the equation.
3FeX2+2Na3Y→1Fe3Y2+NaX
We have 6 X groups on the left hand side. We need 6 X groups on the right hand side of the equation.
3FeX2+2Na3Y→1Fe3Y2+6NaX
All atoms and groups are now balanced.
The balanced equation is:
3FeX2+2Na3Y→Fe3Y2+6NaX
Now all we have to do is re-insert the original groups represented by X and Y. We get
3Fe(NO3)2+2Na3PO4→Fe3(PO4)2+6NaNO3
