Tabulations of chemical elements differing in their organization from the traditional seen periodic system
Answer: 72 grams of
are needed to completely burn 19.7 g 
Explanation:
According to avogadro's law, 1 mole of every substance weighs equal to molecular mass and contains avogadro's number
of particles.
To calculate the number of moles, we use the equation:

Putting in the values we get:


According to stoichiometry:
1 mole of
requires 5 moles of oxygen
0.45 moles of
require=
moles of oxygen
Mass of 
72 grams of
are needed to completely burn 19.7 g 
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The first step is to balance the equation:
<span>C3H8 + 5O2 ---> 3CO2 + 4H2O
Check the balance
element left side right side
C 3 3
H 8 4*2 = 8
O 5*2=10 3*2 + 4 = 10
Then you have the molar ratios:
3 mol C3H8 : 5 mol O2 : 3 mol CO2 : 4 mol H2O
Now you have 40 moles of O2 so you make the proportion:
40.0 mol O2 * [3 mol CO2 / 5 mol O2] = 24.0 mol CO2.
Answer: option D. 24.0 mol CO2
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