Given the unbalanced reaction: NH3 + O2 N2 + H2O. When properly balanced, the sum of the balancing coefficients is 8. 12. 15. 14.

First balance the equation:

4NH3 + 3O2 ↔ 2N2 + 6H2O

Check that the equation is balanced properly by checking the numbers of each element are equal:

LS

N - 1x4 = 4

H - 3x4 = 12

O - 2x3 = 6

RS

N - 2x2 = 4

H - 2x6 = 12

O - 1x6 = 6

Given the equation is balanced properly, we can find the sum of the coefficents by adding.

4 + 3 + 2 + 6 = 15

Therefore, the sum of the coeffiecents is 15.