Gas Stoichiometry and Partial Pressures

Grade 11 · Chemistry

Semester 1 | Period 2 | Week 9

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Subject: Chemistry

Semester: 1

Period: 2

Week: 9

School Name:
Teacher’s Name:
Subject: Chemistry
Grade Level: Grade 11
Week & Period: Week 9, Period II
Date:

Topic: Gas Stoichiometry and Partial Pressures
Sub-topic:

  • Gas Stoichiometry
  • Molar Mass of Gases
  • Dalton’s Law of Partial Pressures

Learning Objectives
By the end of the lesson, learners should be able to:

  1. Apply stoichiometric principles to gas reactions
  2. Calculate the molar mass of a gas
  3. State and apply Dalton’s Law of Partial Pressures
  4. Solve problems involving gases collected over water

Previous Knowledge
Students understand the basic gas laws and the Ideal Gas Equation.

Instructional Materials

  • Balance scale and sample containers
  • Burette, gas syringe
  • Table of molar masses
  • Chart of common gas reactions

Anticipation (Warm-Up) – 5 minutes
Ask:

  • "How can we find the mass of an unknown gas sample?"
  • "What happens when two gases mix in the same container?"

Building Knowledge (Main Lesson) – 25 minutes

  1. Gas Stoichiometry: Apply stoichiometric relationships to gas reactions. Use volume ratios at STP (Standard Temperature and Pressure: 0°C, 1 atm) where 1 mole = 22.4 L.
  2. Molar Mass of a Gas: Use the ideal gas law to derive the molar mass (M = mRT/PV). Demonstrate with a known sample.
  3. Dalton’s Law of Partial Pressures: The total pressure of a mixture of gases equals the sum of the partial pressures of the component gases. Equation: P_total = P1 + P2 + P3 + ...
  4. Gas Collection Over Water: Adjust total pressure by subtracting water vapor pressure.

Learners’ Activities

  • Solve stoichiometric problems involving volumes and mass
  • Use the molar mass formula to calculate unknown gas identity
  • Perform calculations with Dalton’s Law, adjusting for water vapor

Consolidation (Review and Assessment) – 10 minutes

  • Quick quiz on gas law applications
  • Ask learners to explain how to calculate molar mass using experimental data
  • Pose: “How do you find the pressure of dry gas collected over water?”

Homework / Assignment:

  1. A reaction produces 44.8L of CO2 at STP. How many moles is this?
  2. A gas weighs 5.6g and occupies 4L at 273K and 1 atm. Find its molar mass.
  3. A mixture contains oxygen and nitrogen. If their partial pressures are 300mmHg and 450mmHg respectively, what is the total pressure?

Notes – Detailed and Explained
Gas Stoichiometry involves using balanced chemical equations and gas laws to predict the amount of gas involved in a reaction, either by volume or mass.

Molar Mass of a Gas can be found by rearranging the ideal gas law to M = mRT/PV. This allows us to determine the identity of a gas sample.

Dalton’s Law of Partial Pressures is used to calculate the total pressure in a gas mixture. Each gas exerts a part of the total pressure based on its quantity. When gases are collected over water, the vapor pressure of water must be subtracted from the total.

Expanded Notes / Instructions:

  • Reinforce molar volume at STP for quick estimates
  • Use Dalton’s Law with real gas collection lab data if available
  • Emphasize balancing equations in stoichiometric calculations

Inclusive / Differentiation

  • Sample gas data for hands-on calculation
  • Step-by-step guides for molar mass problems
  • Group problem-solving challenges for peer support

Teacher’s Reflection (Post-Lesson Questions)

  • Were students able to apply stoichiometry to gases?
  • Did they grasp the adjustment for vapor pressure?
  • Which learners need more examples to master Dalton’s Law?