Question

1964 PC13(g) + Cl2(g) AH = 92.5 kJ/mol Predict the direction of the shift in equilibrium in the following situations: (a) The temperature is raised. the system shifts from left to right o the system shifts from right to left O no effect (b) More chlorine gas is added to the reaction mixture. the system shifts from right to left O no effect the system shifts from left to right (c) Some PCIz is removed from the mixture. the system shifts from left to right the system shifts from right to left no effect o (d) The pressure on the gases is increased. the system shifts from right to left no effect the system shifts from left to right (e) A catalyst is added to the reaction mixture. the system shifts from right to left no effect the system shifts from left to right

Answer 1

Temperature is raised -- since ∆H is positive, this reaction is endothermic. On increasing the temperature reaction moves forward. Equilibrium shifts towards right. The system shifts from left to right.

According to Le Chatelier's principle if a system at equilibrium is subjected to a stress then the system behaves in such a way so as to reduce the stress. Effect of temperature : When temperature is increased then reaction shifts in that direction which absorbs heat and reduces temperature. In an exothermic reaction when temperature is increased then reaction shifts towards left direction and vice versa. In an endothermic reaction when temperature is increased then reaction shifts in right direction. Effect of pressure : When pressure increases volume decreases hence no. Of moles increases and reaction shifts in such a direction so as to reduce the number of moles i.e reaction shifts towards that side which have lesser no. of moles. Concentration : When concentration of product increases then reaction shifts towards product side and vice versa. When concentration of reactants increases then reaction shifts towards product side and vice versa. Catalyst : No effect on equilibrium.

More chlorine gas is added -- On increasing Chlorine concentration , reaction moves in backward direction. System shifts from right to left.

PCl3 is removed -- On increasing PCl3 concentration , reaction moves in the backward direction. Equilibrium shifts towards left. System shifts from right to left.

Pressure on the gas is increased -- On increasing the pressure , volume decreases and number of increases , reaction moves in that direction which has lesser number of moles. Reaction moves backward. System shifts from right to left.

Catalyst is added -- No effect in equilibrium. No effect