Some Basic Concepts of Chemistry Test - 11

Calculations:

Mass of 1mole of  O₂

  =  the mass of 6.022 x 10²³  molecules  of  O_{2     '} ( as per Avogadro's law )

= molar mass of O₂  in grams ( ie. gram molar mss )

=  32 .0  g  

Since , the number of molecules contained in one mole of a substance

 =  Avogadro's number  (N)

 =   6.022 x 10²³  molecules ,

and  , gram molar mass of water

= 18 g  

∴18g H₂O =   1mol water

∴ one mol of water would contain

= 6.022 x 10²³ molecules of water 

As per  stoichiometry of the reaction ,

 One  mole of Fe ₂ O₃   is  needed to react with three moles of CO .   An excess of reagent is necessary to permit the reaction to go to completion .  Hence , if  Fe₂ O₃   is not taken  in excess it would be   consumed  first .  So it is present in relatively   lesser  amount than the required .  Thus , Fe₂ O₃  is limiting reagent. 

Chemical reactions rarely occur completely when exactly the right amounts of reactants are taken to react together to yield products as per its stoichiometry. One of the reactants  will be used up, before another runs out. Thus, the reactant which  is consumed first is known as limiting reagent 
For  the given reaction ,
2N₂H₄ (l) + N₂O₄ (l) → 3N₂ (g) + 4H₂O (l)
as per its stoichiometry, if only the right and exact amount of N₂O₄ is taken, the reaction may not go to completion. As such it would be consumed first & is, therefore, the limiting reagent. 

Chemistry does not deal in explaining superconductivity.

*In superconducting materials the charecteristics of superconductivity appear when the temperature is lowered below a critical temperature.

*The onset of superconductivity is accompanied  by abrupt changes in physical properties which are more related to phase transitions of the material .

These aspects of  studies in properties of materials  are better related to studies in the fields of Physics , eventhough  principles involved in Chemistry & Physics go hand to hand.