Question

determine the activation energy, Ea, of the decomposition reaction, CH3CHO

Answer 1

From Ahrrenius equation;

K1 = A*exp(-Ea/(RT1))

K2 = A*exp(-Ea/(RT2))

Note that A and Ea are the same, they do not depend on Temperature ( in the range fo temperature given)

Then

Divide 2 and 1

K2/K1 = A/A*exp(-Ea/(RT2)) / exp(-Ea/(RT1))

Linearize:

ln(K2/K1) = -Ea/R*(1/T2-1/T1)

get rid of negative sign

ln(K2/K1) = Ea/R*(1/T1-1/T2)

substitute

ln(0.0315/0.0025) = Ea/8.314*(1/(390+273) - 1/(470+273))

Ea = ln(0.0315/0.0025) *8.314/(1/(390+273) - 1/(470+273))

Ea = 129711.06 J/mol

Ea = 129.7 kJ/mol