To determine the atomic mass of an element, the masses of all the naturally occurring isotopes of that element are averaged together. why are some isotopes more heavily weighted than others? a. they occur more frequently in nature. b. they have a higher mass. c. they have a higher number of orbitals. d. they have more protons.

Nitric acid can be formed in two steps from the atmospheric gases nitrogen and oxygen, plus hydrogen prepared by reforming natural gas. in the first step, nitrogen and hydrogen react to form ammonia: (g) (g) (g) in the second step, ammonia and oxygen react to form nitric acid and water: (g) (g) (g) (g) calculate the net change in enthalpy for the formation of one mole of nitric acid from nitrogen, hydrogen and oxygen from these reactions. round your answer to the nearest .