To completely convert 9. 0 moles of hydrogen gas (h2) to ammonia gas, 3.0 moles of nitrogen gas (n2) are required.
<h3>What are moles?</h3>
The mole is a SI unit of measurement that is used to calculate the quantity of any substance.
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The given reaction is 
By the stoichiometry rule of ratio hydrogen: nitrogen
3 : 1
The reacted moles of nitrogen is equals to H/3 moles of reacted hydrogen
 
So, moles of nitrogen  

Thus, 3.0 moles of nitrogen gas (n2) are required.
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the mass of aluminum oxide (101.96 g/mol) produced from 1.74 g of manganese(iv) oxide (86.94 g/mol) is 1.36g
The reaction is 3 MnO2 + 4 Al ------ 2Al2o3+ Mn
3 mole of manganese oxide give 2 moles of aluminum oxide so by the reaction n( MnO2)/3 =n(al203)2
the formula is n= mass/M so, now substituting values 
m (Al2O3)= m(MnO2) X 2 X M (Al2O3) / M(MnO2 X3
so, by substituting values, 2 X101.96 X1.74g / 3 X 86.94 =1.36g 
so mass of aluminum oxide obtained = 1.36g
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The melting of solid wax to form liquid wax and the evaporation of liquid wax to form wax vapor are physical changes. The burning of the wax vapor is a chemical change.