What is the potentual energy of 7 kg object, 12 m off the ground?

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

Which of the following characteristics are true of enzymes? check all that apply. a.)the structure of an enzyme can change if conditions change. b.)a single enzyme can normally catalyze a wide variety of reactions under many conditions. c.)enzymes are found only in nonliving systems. d.)enzymes allow living things to regulate body conditions through feedback mechanisms. e.)enzymes bind to specific substrates in specific ways. f.)enzymes increase the rate of reaction. g.)when shown in energy-reaction diagrams, enzymes represent the higher activation energy.

How do you calculate the mass of a product when the amounts of more than one reactant are given?