Question

How do you do gas stoichiometry problems at STP?

Answer 1

Hint:As we know that at standard temperature and pressure, 1 mole of gas will occupy a volume of 22.4 L. This relation can be used to convert the between the terms mass, volume and number of moles.

Complete step by step answer:The gas stoichiometry problem gives a relation between the number of moles of the reactant and product in a chemical reaction. It involves the chemical reaction which produces gases.
The ideal gas law and balanced chemical equation is used to calculate the number of moles, calculate the amount in volume and mass.
The stoichiometry calculation which involves gases helps to convert between the mass, number of moles, volume of gases.
The relation used is that at standard temperature and pressure (STP), 1 mole of gas will occupy a volume of 22.4 L.
Example: $4N{H}_3(g)+7O_2(g)\to 4N{O}_2(g)+6H_{2}O(l)$
Here we have to calculate the volume of $N{O}_2$ produced from the combustion of 100 g of $N{H}_3$where the reaction takes place at standard pressure and temperature.
From the periodic table, we can determine the molar mass of ammonia with is 17 g/mol and so the stoichiometric calculation is done as shown below.
$\Rightarrow (100gN{H}_3)\times \left({\displaystyle \frac{1molN{H}_3}{17g}}\right)\times \left({\displaystyle \frac{4molN{O}_2}{4molN{H}_3}}\right)\times \left({\displaystyle \frac{22.4L}{1molN{O}_2}}\right)$
$\Rightarrow 132LN{O}_2$
As the reaction is taking place at STP, the volume 22.4 L can be related to the 1 mol $N{O}_2$.

Note:
The stoichiometry of the reaction is based on the principle of the law of conservation of energy which states that the mass of the reactant must be equal to the mass of the product. This assumption is used to solve unknown quantities of reactants and products.