Question

If delta H rxn is -75.2 kJ, 2NO(g) + Cl2 (g) <---> 2NOCl(g) A scientist places four moles of nitrogen monoxide and two moles of chlorine gas into flask A and the same amounts into Flask B, then allows the systems to reach equilibrium. Flask A is at 25 degrees Celsius and Flask B is at 200 degrees Celsius

A) In which flask will the reaction occur faster? Explain.

B) In which flask will the reaction occur to a greater extent? Explain.

Answer 1

a)

Rate of a reaction is determined by the rate constant k which is given by the Arrhenius equation.

k = Ae^-Ea/RT where A is the pre exponential constant, Ea is the activation energy , R is the gas constant, T is the temperature.

If we increase the temperature T we are decreasing the value Ea/RT (greater denominator)

which increases the value of k as k = A/(e^Ea/RT) (decreasing denominator)

so, increasing temperature will increase the rate of reaction. Reaction in Flask B will be faster.

b)

As H rxn is negative we know that this reaction releases energy and thus an exothermic reaciton.

If we increase temperature the equilibium will shift in the direction such as to minimize this increase and thus go backwards as backward direction reaction will be endothermic and thus will compensate the extra heat. So, extent of completion of reaction will decrease if we increase the temperature.

So, Flask A will have reaction completing to more extent compared to reaction in flask B