SCH 3U - Gas Stoichiometry, Part 2

Recall that, according to Avogadro’s Law, n ∝ V.  This means that in some stoichiometric calculations, we can set up volume ratios instead of mole ratios.  It makes these types of calculations quick and simple.

ex.  Gaseous water can be produced by the reaction of hydrogen gas with oxygen gas at STP conditions.  If 4.5 L of oxygen gas is reacted with 9.5 L of hydrogen gas, what volume of water is produced?

2H₂(g)             +             O₂(g)            →             2H₂O(g)

STP                                STP                              STP

V = 9.5 L                        V = 4.5 L                       V = ?

CF = 9.5/2                     CF = 4.5/1                 V_H2O/2 = V_O2/1

= 4.75                                  = 4.5                       V_H2O = 2 (4.5 L)

   XS                                    LIM                                   = 9.0 L

There are a couple of stipulations that must be met to carry out your stoichiometric calculations this way:

1. The conditions must remain the same throughout the reaction. For instance, in the reaction above, both reactants and products are found under STP conditions. 
2. The substances, for which you are doing calculations, must be in the gas state.

Homework:

1.  The gas ethane, C₂H₆, burns in oxygen to form carbon dioxide and water.

(a)   What volume of carbon dioxide will be formed from 10 L of ethane, all at STP?

(b)   If 14 L of ethane and 14 L of oxygen are brought together and ignited, what will be the total volume of products measured at STP?  Assume water is in the gaseous state.

2.  Calculate the volume of nitrogen dioxide gas produced when 0.813 L of nitrogen (III) oxide reacts with excess oxygen gas.  The reaction occurs at 250°C and 160 kPa.

3.   Acetylene burns in oxygen, according to the equation, 2C₂H₂(g)  +  5O₂(g)  →  4CO₂(g)  +  2 H₂O(g).

(a)   At STP, what volume of oxygen gas will react completely with 44.8 L of acetylene?

(b)   What volume of carbon dioxide gas is produced when 22.4 L of acetylene reacts at STP?

 
Answers: