Question

63. Ethylene, C2H4, used to make polyethylene plastics, can be made from ethane, C2H6, one of the components of natural gas. The heat of reaction for the decomposition of ethane gas into ethylene gas and hydrogen gas is 136.94 kJ per mole of C2H4 formed, so it is endothermic. The reaction is run at high temperature, in part because at 800-900 °C, the equilibrium constant for the reaction is much higher, indicating that a higher percentage of products forms at this temperature. Explain why increased temperature drives this reversible chemical reaction in the endergonic direction and why this leads to an increase in the equilibrium constant for the reaction. C2H6(g) = C2H4(g) + H2(g)

Answer 1

Equilibrium constant of a reaction is independent of the concentration of the starting material and the product, but it is dependent upon the temperature of the reaction. A reaction occurs by collision between the reactant molecules. At lower temperature individual molecules of substrates have certain amount of kinetic energy. The molecules thus move with certain speed and may collide to form the product. When we increase the temperature of the reaction, the heat supplied is absorbed by the substrate molecules which increases its kinetic energy and thus moelcules now move at a greater speed. Chances of collision increases between the substrate molecules which increases the rate pf product formation and thus increases the equilibrium constant of the reaction which signifies the probability of reactant to go to product side. Thus we see an increase in the equilibrium constant for the reaction given above.