AP Chemistry Questions: Ideal Gas Law and Stoichiometry

📚 Quick Study Guide

• ⚛️ The Ideal Gas Law: $PV = nRT$, where:
  • $P$ = Pressure (atm, kPa)
  • $V$ = Volume (L)
  • $n$ = Number of moles
  • $R$ = Ideal gas constant (0.0821 L atm / (mol K) or 8.314 L kPa / (mol K))
  • $T$ = Temperature (K)
• 🌡️ Temperature Conversion: Always use Kelvin in gas law calculations. $K = °C + 273.15$
• ⚖️ Stoichiometry: The quantitative relationship between reactants and products in a chemical reaction.
  • Use mole ratios from balanced equations.
  • Convert mass to moles using molar mass.
• 💨 Standard Temperature and Pressure (STP): 0°C (273.15 K) and 1 atm. At STP, 1 mole of any ideal gas occupies 22.4 L.
• 💡 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. $P_{total} = P_1 + P_2 + ... + P_n$

🧪 Practice Quiz

1. A gas occupies 10.0 L at STP. How many moles of gas are present?
   1. 0.224 mol
   2. 0.446 mol
   3. 2.24 mol
   4. 4.46 mol
2. What volume will 2.0 moles of an ideal gas occupy at 27°C and 2.0 atm?
   1. 11.2 L
   2. 22.4 L
   3. 24.6 L
   4. 33.6 L
3. If 4.0 g of hydrogen gas ($H_2$) reacts completely with oxygen to form water, how many grams of water ($H_2O$) are produced? (Molar mass of $H_2 = 2.0 g/mol$, $H_2O = 18.0 g/mol$)
   1. 9.0 g
   2. 18.0 g
   3. 36.0 g
   4. 72.0 g
4. A container holds a mixture of nitrogen gas ($N_2$) at a partial pressure of 300 mmHg and oxygen gas ($O_2$) at a partial pressure of 400 mmHg. What is the total pressure in the container?
   1. 100 mmHg
   2. 350 mmHg
   3. 700 mmHg
   4. 1200 mmHg
5. What is the density of methane gas ($CH_4$) at STP? (Molar mass of $CH_4 = 16.0 g/mol$)
   1. 0.714 g/L
   2. 0.800 g/L
   3. 1.42 g/L
   4. 1.60 g/L
6. If 5.0 L of a gas at 2.0 atm and 27°C is compressed to 2.5 L and cooled to -23°C, what is the final pressure?
   1. 1.0 atm
   2. 2.0 atm
   3. 3.6 atm
   4. 4.0 atm
7. How many liters of oxygen gas ($O_2$) are required to completely react with 10.0 L of hydrogen gas ($H_2$) to form water, assuming both gases are at the same temperature and pressure? $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$
   1. 2.5 L
   2. 5.0 L
   3. 10.0 L
   4. 20.0 L