Lecture Notes: Combined Gas Law

Overview

• The video covers the combined gas law, including:
  • When to use it.
  • Ensuring units are consistent.
  • Correct mathematical approaches.

When to Use the Combined Gas Law

• Initial and Final Conditions: Use when you have both initial and final conditions of a gas.
• Problem Example:
  • Initial Volume: 2.3 L
  • Initial Pressure: 1.3 ATM
  • Asked to find final volume when pressure is increased to 4.7 ATM.
  • Constant Temperature: Ignore temperature in this scenario.

Application of Boyle's Law

• Steps:
  • Substitute given values into the equation.
  • Isolate V2 by dividing both sides by 4.7 ATM.
  • Cancel out units of ATM, leaving liters.
  • Result: V2 = 0.64 L

Key Point

• Constant Conditions: When a variable is held constant, it can be omitted from the combined gas law.

Example Problem with Temperature

• Variables Given:
  • Volume
  • Temperature
  • Pressure remains constant (omit it).
• Temperature Conversion:
  • Convert Celsius to Kelvin by adding 273.
  • Always work with Kelvin for gas laws.
• Solving Process:
  • Set up equation.
  • Solve for V2 by multiplying and dividing correctly.
  • Result: V2 = 3.13 L

Another Example

• Initial Conditions:
  • Units in Celsius and mmHg need conversion.
• Conversion Steps:
  • Celsius to Kelvin: Add 273.15.
  • mmHg to Atmospheres: Divide by 760 (conversion factor: 1 ATM = 760 mmHg).
  • Ensure all units are consistent.
• Calculations:
  • Solve for V2 using the consistent units.
  • Result: V2 = 8.6 L

Important Reminders

• Consistency in Units: Ensure all variables are in the same units for successful calculations.
• Kelvin: Always convert temperatures to Kelvin when dealing with gas laws.