Consider the reaction- N2 (g) + 3H2 (g) = 2NH3 + heat.
Indicate the direction in which the equilibrium will shift when
(a) temperature is increased.
(b) pressure in increased.
N2 (g) + 3H2 (g) 2NH3 (g) + heat.
The reaction is exotheremic in nature.
Effect of temperature: According to Le Chatelier principle, the equilibrium will move in such a way as to counteract the change, so, on increasing the temperature:
1) If the reaction is exothermic (heat is relesing during reaction), then rate of reaction decreases, so reaction proceeds in backward direction. If the reaction is endothermic (ie heat is absorbing during reaction), then rate of reaction increases, so reaction proceeds in forward direction.
Effect of pressure: According to Le Chatelier principle, on increasing the pressure, the equilibrium will move in such a way as to counteract the change i.e. the position of equilibrium will move in such a way that the pressure is reduced again. The more molecules present, the higher the pressure will be. Therefore system can reduce the pressure by reacting in a way to produce fewer molecules.
number of gaseous molecules in reactant side : 1 + 3 = 4
number of gaseous molecules in product side : 2
so, on increases pressure, reactant molecules will feel more pressure due to which reaction will proceed in forward direction so as to reduce the pressure on reactant molecules.