CHAPTER 3. REACTION RATES 3.7
NH 3 N 2 H 2
Start of reaction 1.4 0 0
Used up 0.8 0 0
Produced 0 0.4 1.2
Equilibrium 0.6 0.4 1.2Step 5 : Using the values in thetable, calculate [N 2 ] and [H 2 ][N 2 ] =
n
V=
0. 4
2
= 0. 2 mol· dm−^3[H 2 ] =
n
V=
1. 2
2
= 0. 6 mol· dm−^3Step 6 : Calculate KcKc=[H 2 ]^3 [N 2 ]
[NH 3 ]^2
=
(0.6)^3 (0.2)
(0.3)^2
= 0. 48
Example 5: Calculating Kc
QUESTIONHydrogen and iodine gas react according to thefollowing equation:
H 2 (g) + I 2 (g)� 2 HI (g)
When 0.496 mol H 2 and 0.181 mol I 2 are heated at 450 ◦C in a 1 dm^3 con-
tainer, the equilibrium mixture is found to contain 0.00749 mol I 2. Calculate
the equilibrium constant for the reaction at 450 ◦C.SOLUTIONStep 1 : Calculate the number of moles of iodine used in the reaction.
Moles of iodine used = 0. 181 − 0 .00749 = 0. 1735 molStep 2 : Calculate the numberof moles of hydrogen that are used up in
the reaction.
The mole ratio of hydrogen:iodine = 1 : 1, therefore 0.1735
moles of hydrogen mustalso be used up in the reaction.Step 3 : Calculate the numberof moles of hydrogeniodide that are
produced.
The mole ratio of H 2 :I 2 :HI = 1 : 1 : 2, therefore the numberof
moles of HI produced is 0. 1735 × 2 = 0. 347 mol.
So far, the table can be filled in as follows: