Predicting the Volume of a Gaseous Product

Using a combination of stoichiometry and the ideal gas equation, we can calculate the volume of gas that we expect to be produced in a chemical reaction. We first use stoichiometry to determine the number of moles produced, and then apply the ideal gas equation to determine what volume will be occupied by that number of moles under the specified conditions. 

Sample Problem 11.10 shows how to predict the volume of a gaseous product. 

The air bags in cars are inflated when a collision triggers the explosive, highly exothermic decomposition of sodium azide (NaN,)  

A typical driver-side air bag contains about 50 g of NaN3. Determine the volume of Nt gas that would be generated by the decomposition of 50.0 g of sodium azide at 85°C and 1 atm. 

Strategy Convert the given mass of NaNs to moles, use the ratio of the coefficients from the balanced chemical equation to detennine the conesponding number of moles of Nt produced, and then use the ideal gas equation to detennine the volume of that number of moles at the specified temperarnre and pressure. 

Practice Problem A The chemical equation for the metabolic breakdown of glucose (C HisOg) is the same as that for the combustion of glucose [M4 Section 3.3—Bringing Chemistry to Life box]  

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In other words, one mole of NG produces 7.25 molar volumes of gas (since a molar volume is the volume of one mole of gas). These molar volumes at 0°C and latm form an actual volume of 7.25 x 22.4 = 162.4 liters of gas (provided the products H20 and C02 are in gaseous form). Thus, volume of the products of explosion can be predicted for any quantity of explosive. Further, by employing Charles Law for perfect gases, the volume of the products of explosion may be calculated for any given temperature. Therefore,... 

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