Thursday, September 17, 2015

If you have 66.6 g NH3, how many grams of F2 are needed to consume all the NH3?

The balanced equation for this reaction is:


  + -> +


Step 1: Determine the molar mass of and .


Since "grams" are involved in this calculation, we will need to use the following mole conversion factors: 1 mole = molar mass AND 1 mole = molar mass . So, before we start the main calculation, let's go ahead and determine the molar mass...

The balanced equation for this reaction is:


  + -> +


Step 1: Determine the molar mass of and .


Since "grams" are involved in this calculation, we will need to use the following mole conversion factors: 1 mole = molar mass AND 1 mole = molar mass . So, before we start the main calculation, let's go ahead and determine the molar mass of and .


The molar mass of a substance is determined by multiplying the atomic mass of each atom in the substance times its subscript and adding the resulting answers.


   Molar mass of = (1)(14.007) + 3(1.008) = 17.031 g/mol


   Molar mass of = (2)(18.998) = 37.996 g/mol


Therefore,


   1 mole = 17.031 grams


   1 mole = 37.996 grams


Step 2: Determine the mole ratio between and .


The mole ratio between two substances is equal to the ratio between the coefficients of the substances. According the reaction above, the coefficient for is 2 and the coefficient for is 5. 


Therefore, the mole ratio between and is:


   2 moles = 5 moles


Step 3: Perform the stoichiometry calculation.


The stoichiometry calculation will take the general form of:


  given amount  x   mole conversion factor  x  mole ratio  x   mole conversion factor


Therefore, 


   66.6 g x (1 mol/17.031) x (5 mol /2 mol ) x (37.996 g/1mol) = 371 g


*Notice that the conversion factors and mole ratio are oriented such that all units and substances cancel out except grams of .

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