3 Questions around this concept.
In a 25 L container, 15 moles of $\mathrm{N}_2$ reacted with 12 moles of $\mathrm{H}_2$ at 800 K . It was observed that 6 moles of $\mathrm{H}_2$ was present after equilibrium. The gaseous mixture was suddenly cooled to 300 K after addition of 4.35 L of $\mathrm{H}_2 \mathrm{O}(l)$ in the mixture. What will be the final pressure of the mixture keeping in mind the following points.
- All $\mathrm{NH}_3$ dissolved in water.
- There is no change in volume of the liquid.
- No reaction took place between $\mathrm{N}_2$ and $\mathrm{H}_2$ at 300 K
Also, neglect the V.P. of the liquid solution.

It was introduced by Guldberg and Waage. It states that “the rate at which a substance reacts is directly proportional to its active mass and the rate at which substances react together is directly proportional to the product of their active masses each raised to a power which is equal to the corresponding stoichiometric number the substance present in the chemical reaction".
If active masses of A, B, C and D are [A], [B], [C] and [D] respectively, then:
Rate of reaction of A ∝ [A]
Rate of reaction of B ∝ [B]
V1 ∝ [A] [B] = K1 [A][B]
V2 ∝ [C] [D] = K2 [C][D]
NOTE: Law of mass action is not applicable for solids as for them active mass is always one.
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