Question

Methane is a greenhouse gas and it is predicted to have a large global warming impact. Methane is primarily removed by reaction with hydroxyl radical (OH). OH + CH4 → H2O + CH3 Its activation energy is determined to be 27.2 kJ/mole and rate constant for kch4= 4.75x10-14 molecule cm sec1 at 0.00 °C. Assuming typical OH concentration in troposphere is 1.0x106 molecules cm A. Determine the atmospheric lifetime of CH4 at 0 °C B. Determine the rate constant at -30.0°C. C. Determine the atmospheric life-time of CH4 at -30.0 °C. D. Suggest one way to lower the activation energy of this reaction

Answer 1

Part B.

According to the Arrhenius equation:

ln(k2/k1) = Ea/R (1/T1 - 1/T2)

i.e. ln(k2/4.75*10^-14) = (27.2*1000 J/mol)/(8.314 J/mol.K) * (1/273 K - 1/243 K)

i.e. ln(k2/4.75*10^-14) = -1.48

i.e. k2/4.75*10^-14 = e^-1.48 = 0.228

i.e. k2 = 4.75*10^-14 * 0.228 = 1.08*10^-14 molecule^-1.cm³.sec^-1

Part D.

The activation energy of this reaction can be decreased by introducing a catalyst, which creates a new pathway to the reaction such that the activation energy of the reaction can be lowered.