according to half life equation:
T(1/2) = ㏑2 / K1
when the T(1/2) = 4 min * 60 = 240 sec
by substitution:
240 = 0.6931 / K1
K1 = 2.9 x 10^-3
when the second T(1/2) = 20 sec, so to get K2:
T(1/2) = 0.6931 / K2
by substitution:
20 = 0.6931 / K2
∴K2 = 3.4 x 10^-2
so, we can get T2 by using this formula:
㏑ (K2/K1) = Ea/R (1/T1 - 1/T2)
by substitution:
㏑(3.4 x 10^-2)/(2.9 x 10^-3) = (24520 / 8.314) (1/298 - 1/T2)
∴ T2 = 396.7 K
= 396.7 - 273 = 123.7 °C
