When the concentration of a is doubled, the rate for the reaction: 2a+b → 2cquadruples..?

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Most materials are not magnetic because their magnetism has worn off. their magnetic domains are arranged randomly. they lack magnetic fields. earth’s heat has destroyed their magnetism.

Under which circumstances are kp and kc equal for the reaction aa(g)+bb(g)⇌cc(g)+dd(g)?