JEE Advanced levelSingle correct optionDifficulty 3 of 3ce048
For NX2(g)+3HX2(g)2NHX3(g) at equilibrium in a rigid vessel, [NX2]=0.50M, [HX2]=0.50M and [NHX3]=0.25M. Then enough NX2 is added to make [NX2]=1.00M and at the same instant NHX3 is removed to make [NHX3]=0.10M ([HX2] unchanged). Which statement describes the situation immediately afterwards?
AQc=0.08, which is less than Kc=1.00, so the net reaction is backward
BQc=0.08, which is less than Kc=1.00, so the net reaction is forward
CQc=12.5, which is greater than Kc=1.00, so the net reaction is backward
DQc=1.00=Kc, so the system stays at equilibrium
Answer: B
Kc=(0.25)2/((0.50)(0.50)3)=1.00. After the changes, Qc=(0.10)2/((1.00)(0.50)3)=0.08. Since Qc<Kc (too much reactant, too little product), the net reaction is forward.