In reaction: 2H₂O(g)⇌2H₂(g)+O₂(g); ∆H=+242 kJ/mol In which direction the equilibrium shifts, if: a. Temperature is increased? b. Temperature is descreased? c. H₂ is added? d. O₂ is reduced? e. Pressure is enlarged?

3 Answers
Nov 26, 2017

Left: a,c,e
Right: b,d


Le Chatelier's principle states that equilirbium shifts to the direction which will counteract the effect of change.

a: If temperature is increased, equilibrium shifts to left, which is endothermic direction.
b It is contrary to a. Equilibrium shifts to right(exothemic direction).
c If #H_2# is added, the system tries to consume #H_2#. Therefore, equilibrium shifts to left.
d Equilibrium shifts to the direction that produces #O_2#. This is right.
e The direction to reduce the pressure is left.

See also:

Nov 26, 2017

a. shift to left
b. shift to right
c. shift to left
d. shift to right
e. shift to left


Reaction shifts are pretty easy to identify if you think of the balanced equation as a literal "balance". Changing something on one side requires something to change on the other side to maintain the balance (equilibrium).

The same is true for thermodynamic (heat) effects. If the reaction requires heat input, adding more will make it proceed faster, and decreasing it will make it go slower.

In this case, the '+' #Delta H# means that it is exothermic - releasing energy in the indicated direction. Thus, adding more heat will make shift it in the reactant (left) direction, and reducing it will shift it to the product (right) direction.

#H_2 and O_2# are both products, so adding either of them will shift the reaction back to the reactants (left) to balance. Removing them will shift it to the products (right).

Pressure affects the reaction rate , but not the equilibrium position. However, le Chatelier's Principle applied to gases will tend to reduce the total molar volume. Thus, higher pressure will shift the reaction to the left (2 molecules) from the right (three molecules).

Nov 26, 2017

The reaction is endothermic so the forward reaction is endothermic.
If the temperature is increased, the equilibrium would shift to the right so more reactant is made and vice versa.

If more hydrogen is added, more water, more reactant is produced so equilibrium shifts to the left.
If Oxygen is reduced, more water will decompose to produce more products so equilibrium shifts to the right.

If pressure is increased, the equilibrium will shift to the side with fewer moles of gas; 2:3 so more water will be formed than products. The equilibrium will shift to the left.