What mass of iron must be in a hot pack to provide -335kj of heat when the iron reacts with oxygen and is converted to iron (111) oxide according to the following thermochemical equation? 2fe(s) + 1.5o2(g)—> fe2o3(s) delta h= -824.2kj/mol

48.1 grams.

How many moles of the reaction is needed to provide that 335 kJ of heat?

How many moles of iron, Fe in 0.4307 moles of the reaction?

What's the mass of 0.8614 moles of iron, Fe?

do u have any choices to choose from ? ?

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.