Gas Stoichiometry Calculations: Step-by-Step Guide with Examples

📚 Quick Study Guide

• ⚖️ Gas stoichiometry involves using balanced chemical equations to determine the amounts of gaseous reactants and products.
• 🌡️ The ideal gas law, $PV = nRT$, is essential. Where $P$ is pressure, $V$ is volume, $n$ is the number of moles, $R$ is the ideal gas constant, and $T$ is temperature (in Kelvin).
• 🔢 Remember to convert temperature to Kelvin: $K = °C + 273.15$.
• 🧪 Standard Temperature and Pressure (STP) is $0°C$ (273.15 K) and 1 atm. At STP, 1 mole of any gas occupies 22.4 L (molar volume).
• ⚗️ Dalton's Law of Partial Pressures: The total pressure of a mixture of gases is the sum of the partial pressures of each individual gas: $P_{total} = P_1 + P_2 + ... + P_n$.
• 💡 When dealing with gas stoichiometry, always start by balancing the chemical equation.

Practice Quiz

1. What volume of oxygen gas ($O_2$) is required to completely combust 10.0 L of methane gas ($CH_4$) at STP, given the following balanced equation?

   $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$

   1. 5.0 L
   2. 10.0 L
   3. 20.0 L
   4. 30.0 L

2. If 5.0 L of nitrogen gas ($N_2$) reacts with excess hydrogen gas ($H_2$) at 300 K and 2.0 atm, what volume of ammonia ($NH_3$) is produced, assuming the reaction goes to completion?

   $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$

   1. 2.5 L
   2. 5.0 L
   3. 10.0 L
   4. 15.0 L

3. How many grams of $CO_2$ are produced from the complete combustion of 11.2 L of $C_2H_2$ at STP?

   $2C_2H_2(g) + 5O_2(g) \rightarrow 4CO_2(g) + 2H_2O(g)$

   1. 22 g
   2. 44 g
   3. 88 g
   4. 176 g

4. A container holds 2.0 g of $H_2$ gas and 32.0 g of $O_2$ gas. The total pressure in the container is 3.0 atm. What is the partial pressure of $H_2$?

   1. 0.5 atm
   2. 1.0 atm
   3. 2.0 atm
   4. 2.5 atm

5. What mass of potassium chlorate ($KClO_3$) must be decomposed to produce 4.8 L of oxygen gas at STP?

   $2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$

   1. 6.1 g
   2. 12.2 g
   3. 18.3 g
   4. 24.4 g

6. If 10.0 L of hydrogen sulfide gas ($H_2S$) is burned in excess oxygen at 25°C and 1 atm, what volume of sulfur dioxide ($SO_2$) is produced?

   $2H_2S(g) + 3O_2(g) \rightarrow 2SO_2(g) + 2H_2O(g)$

   1. 5.0 L
   2. 10.0 L
   3. 15.0 L
   4. 20.0 L

7. What is the density of methane gas ($CH_4$) at 27°C and 2 atm?

   1. 0.65 g/L
   2. 1.31 g/L
   3. 2.61 g/L
   4. 3.22 g/L