Question

Predict how the equilibrium will shift (to the left, to the right or no change) with each of the following stresses: a. 2H2 (g) + 2NO (g) → N2 (g) + 2H2O (g) i. Increase [H2] ii. Decrease [NO] iii. Decrease the pressure (by increasing the volume) b. CO (g) + 1/2O2 (g) → CO2 (g) + 283 kJ i. Decrease temperature ii. Increase pressure (by adding He (g)) c. H2O (l) → H + (aq) + OH− (aq) i. Add NaOH d. 4NH3 + 5O2 (g) → 4NO (g) + 6H2O (g) + energy i. Increase temperature ii. Remove NO (g) e. Fe3O4 (s) + 4H2 (g) ↔ 3Fe (s) + 4H2O (g) i. adding more H2 to the mixture ii. adding more Fe (s) iii. removing H2 iv. adding a catalyst

Answer 1

for the reaction ; . 2H2 (g) + 2NO (g) → N2 (g) + 2H2O (g)

number of moles of product = 1 + 2 = 3

number of moles of reactants = 2 + 2 = 4

change in moles = number of moles of product - number of moles of reactannt = 3-4 = -1

le chatlier principle : if a system in equilibrium is subjected to a change of concentration , temperature or pressure , the equilibrium will shift in a direction that tends to undo the effect of the change imposed.

i) effect on equilibrium : since H2 is a reactant , on increasing the concentration of reactant , equilibrium will shift in the direction which will decrease the [H2] , hence the reaction will move shift in forward direction.(to the right)

ii) since NO is a reactant , on decreasing the concentration of reactant , equilibrium will shift in the direction which will increase the [NO] , hence the reaction will move shift in backward direction.( to the left)

iii) if the pressure on the system is decreased , the equilibrium will shift in that direction which is accompanied by increase in total number of moles . i.e backward direction.

Qb . reaction . CO (g) + 1/2O2 (g) → CO2 (g) + 283 kJ

i) this reaction is exothermic in forward direction ( heat is released in the forward direction ). if the temperature is decreased ,i.e heat is absorbed, then according to le chatlier principle , the equilibrium will shift in the direction to that side that releases heat i.e in the forward direction.

ii) by adding an inert gas such He , number of moles increases and since n is directly proportional to pressure , the pressure will be increased. if the pressure on the system is increased , then according to le chatlier principle , the equilibrium will shift in that direction in which decrease in total number of moles occurs . ie. forward direction.

c) reaction H2O (l) → H + (aq) + OH− (aq)

i) addition of NaOH : NaOH will dissociate in   Na+ (aq) + OH− (aq) . thus [OH-] will increase . since , OH- is a product , by adding more of it , we are increasing the concentration of a product. To undo this change , the equilibrium will shift in backward direction.

d) reaction : 4NH3 + 5O2 (g) → 4NO (g) + 6H2O (g) + heat

i) increasing temperature : this reaction is exothermic in forward direction ( heat is released in the forward direction ). if the temperature is increased ,i.e heat is supplied to the system , then according to le chatlier principle , the equilibrium will shift in the direction to that side that absorbs heat i.e in the backward direction.

ii) removing NO : since NO is a product, by removing it we are decreasing the concentration of NO . to undo this change, equilibrium will shift to that side where [NO] will increase i.e forward direction.

e) reaction : Fe3O4 (s) + 4H2 (g) ↔ 3Fe (s) + 4H2O (g)

i) addition of H2 : since , H2 is a reactant , by adding more of it , we are increasing the concentration of a reactant. To undo this change , the equilibrium will shift in forward direction.

ii) addition of Fe : sinceFe is a product, by adding it we are increasing the concentration of Fe . to undo this change, equilibrium will shift to that side where [Fe] will decrease i.e backward direction.

iii) Removing H2 (g) – since H2 is a reactant, by removing it we are decreasing the concentration of H2 . to undo this change, equilibrium will shift in backward direction.

iv) addition of a catalyst doesnot disturb the equilibrium. however, it helps in the attainment of equilibrium quickly.