The free radical chlorination of isobutane at 25C yields 64% isobutyl chloride and 36% tert-butyl chloride. However, free radical bromination of the same compound at 127C yields only trace amounts of isobutyl bromide and 99% of tert-butyl bromide, even though the ease of formation and free radical stability is the same for chlorination and bromination. Account for these differences in products. Reactivity ratio for chlorination and bromination are 5.0:3.8:1.0 and 1600:82:1 respectively.