Question

2C8H18+25O2=16CO2+18H2O

How many moles of CO2 are emitted into the atmosphere when 23.1 g of C8H18 is burned?

2. Given the following chemical equation, determine how many grams of N2 are produced by 9.13 g of H2O2 and 5.57 g of N2H4.

2H2O2+N2H4=4H2O+N2

Answer 1

Q.1

Given :

Mass of C8H18 = 23.1 g

Reaction :

2C8H18+25O2-->16CO2+18H2O

The reaction is balanced.

We use reaction stoichiometry to find moles of CO2. For that we consider mole ractio between CO2 with the species whose moles are know. Here mass of C8H18 is given. By using mass we get its moles.

Mole ratio CO2 : C8H18 = 16 : 2 or 8:1

Now #moles of C8H18 = Mass in g / Molar mass of C8H18

= 23.1 g / 114.2302 g per mol                   (Molar mass of C8H18 = 114.2302 g per mol )

= 0.203 mol C8H18

We use mole ratio to get moles of CO2 :

# moles of CO2 = #moles of C8H18 * 8 mol CO2 / 1 mol C8H18

= 1.62 mol CO2

So 1.62 mol CO2 will go in atmosphere when 23.1 g C8H18 is burnt.

Q 2 )

Given :

Mass of H2O2 = 9.13 g

Mass of N2H4 = 5.57 g

Solution:
2H2O2+N2H4-->4H2O+N2
The given reaction is balanced.

Lets calculate moles of both H2O2 and N2H4

# moles of H2O2 = 9.13 g / 34.0138 g per mol

= 0.2684 mol H2O2

#mol N2H4 = 5.57 g / 32.0456 g per mol

=0.1738 mol N2N4

Now if moles of more than one reactants are given then we have to find limiting reactant. The reaction which reacts completely in the reaction and so product formation is completely depends upon the amount of limiting reactant.

From the reaction stoichiometry ,

1 mol N2H4 needs 2 mol H2O2 so, to react 0.1738 mol N2H4 how many moles of H2O2 are required.

# moles of H2O2 required to react with N2H4

= 0.1738 mol N2H4 * 2 mol H2O2 / 1 mol N2H4

= 0.3476 mol H2O2

But actually moles of H2O2 are less than the required.

So H2O2 is limiting reactant.

Lets use moles of H2O2 to find mass of N2.

Mole ratio of H2O2: N2 is 2:1

#moles of N2 = 0.2684 mol H2O2 * 1 mol N2 / 2 mol H2O2

= 0.1342 mol N2

Mass of N2 in g = 0.1342 g N2 * Molar mass of N2

=0.1342 g * 28.014 g per mol

=3.76 g N2

So Mass of N2 produced = 3.76 g