ok so for q31. you're given a bunch of moles and vessel info, so i started by calculating [N2]initial, [H2]initial, [NH3]initial because we have all of that. then we chuck all of that info into an ice table. but one thing to note is that the q is asking you to increase the amount of N2 by a certain amount to increase ammonia by 0.050 moles. so for the initial concentration, you found [N2] = 0.45M. let the number of moles you add be X (don't stress too much that it's moles not concentration, the reaction vessel is a nice clean number anyway you'll see)
Concentration (mol/L) | N2 | 3H2 | 2NH3 |
Initial | 0.45 + X | 0.1 | 0.58 |
Change | -0.0025 | - 0.0075 | +0.0050 moles (this bit is important, remember to divide 0.050 by 10 cos of rxn vessel) |
Equilibrium | 0.4475 + X | 0.0925 | 0.585 |
you know that Keq = 748, and you can make the expression from the given equation. sub in everything and then rearrange to find X. then remember to multiply by 10 to convert it back to moles.
0.4475 + X = (0.585)^2/[(0.0925)^3 x 748]
X = 0.130575... mol/L
n(N2) added to vessel = 0.130575... x 10.0L (n = cV) = 1.30575... = 1.3 mol added (2sf)