Question

Consider the following reaction at equilibrium: (AH° = +92.4kJ) 2NH3(g) = N2(g) + 3H2(0) Le Chateliers Principle predicts that the moles of H2(g) in the reaction container will increase with Select one: O a. an increase in the volume of the reaction (constant T) O b. some removal of NH3(g) from the reaction vessel (constant V and T) O c. addition of some N2(g) to the reaction vessel (constant V and T) O d. an increase in total pressure by the addition of helium gas (constant V and T) O e. a decrease in the total volume of the reaction vessel (constant T)

Answer 1

Le-Chatelier and Braun (1884) , French chemists , made certain generalization to explain the effect of changes in concentration, temperature, volume or pressure on the state of system in equilibrium . When a system is subjected to a change in one of these factors, the equilibrium gets disturbed and the system readjusts itself until it returns to equilibrium . The generalization is known ad Le-Chatelier's principle. It may be stated as:-

Change in any of the factors that determine the equilibrium conditions of a system will shift the equilibrium conditions in such a manner to reduce or to counteract the effect of the change .

Here, given equation is :-

2 NH3 (g) <-----------> N2 ( g ) + 3 H2 ( g )

H2 (g) is present on product side .

Now , Effect of change of Volume of container:

When we decreases the volume , there is increase in pressure . As result , there will be a large number

of moles of gaseous substance per unit volume . The effect of increased number of moles can be undone if the equilibrium shifts in the direction which produces lesser number of gaseous moles .

But when we INCREASES THE VOLUME of reaction vessel, then the number of moles of gaseous substances per unit volume decreases , and these decrease in gaseous moles can be undone if equilibrium shifts in a direction where number of moles increases .

Here in given reaction , the number of moles of gaseous substance are 2 ( in 2 NH3 (g) ) while in product side we have 4 moles of gaseous substance ( one N2 (g) and three H2(g) ) . So we have greater number of gaseous products. So when we increases the volume of reaction then moles per unit volume of gaseus substance decreases which can be undone when more gaseous moles are produced . So basically equilibrium shifts to product side and hence more moles of N2 and H2 are formed .

so Le-Chatelier's principle predicts that moles if H2 ( g) in reaction will increases when volume of reaction is increased .

So option A is correct answer .