Question

For the reaction below, describe the temperature and pressure conditions that would produce the highest yield for the forward reaction. Explain your answer in terms of Le Châtelier’s principle.

N2 (g) + 3 H2 (g) Two arrows stacked on top of each other. The top arrow points to the right. The bottom arrow points to the left. 2 NH3 (g) deltaH = -92 kJ/mol

Answer 1

@Somy I know the temperature shift is determined whether the reaction is endothermic or exothermic and I know that for pressure the system will shift in the direction that decreases the total of moles of gas. But how can tell if it's endothermic or exothermic and if it decreases?

Answer 2

It's exothermic reaction as delta H is negative for the forward reaction

Answer 3

Can someone check my answer?

The reaction is exothermic and by lowering the temperature it will move the reaction towards the product. By increasing pressure more products will be created.

Answer 4

Yeah u r right

Answer 5

not 'move the reaction' but
The reaction is Exothermic because Delta H is negative
thus it means if we decrease the temperature equilibrium position will, favor production of product giving high yield/ shift to the right
if we increase the pressure equilibrium position will shift to the right/ favor production of product


now reasoning :
to initiate any kind of reaction usually we provide energy
this energy is required for braking down compounds to atoms/ions
only after that any reaction can take place
after the reaction happens between these atoms/ions and the product is formed- the energy that we originally provided is released.



if the reaction is EXOTHERMIC
that means that the energy you originally GAVE is LESS than energy that was RELEASED after the product was formed
in other words the energy RELEASED was MORE than energy given


if the reaction is ENDOTHERMIC
that means that the energy you originally GAVE is MORE that energy that was RELEASED after the product was formed
meaning the energy RELEASED was LESS than energy given


so in your case the energy released was more than energy provided (that negative sign shows it) thats why this reaction is Exothermic





Now look
lets say its Endothermic reaction
and we know that in Endothermic reaction - energy given is more than energy released
so that means to form a product we need to provide a huge amount of energy , that is why - in Endothermic reaction increasing the temperature would favor product formation and decreasing would favor reactant production.


now lets say its Exothermic reaction
we know that in Exothermic reaction - energy given is less than energy released
so this means that not much energy is required to initiate the reaction and form a product
thats why decreasing the temperature would favor product formation and increasing would cause Products to decompose to reactants thus favor reactant formation





Now about pressure
imagine you have a square box
it has something in it
now imagine you crashed that box
the content of the box would get closer to each other right?
this is way as we INCREASE the pressure
atoms/reactants meaning are closer to each other thus because of this pressure Collision of particles is very strong/ with huge force
this is the reason why 'collision is successful' meaning we get the product so as we increase the pressure rate of production of product is faster and we get more product (in a given time)

i hope it makes sense :)