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.