Gas Laws Objectives

Gas Laws

• Gas pressure changes with volume, temperature, and amount of gas molecules
• To determine gas pressure changes, identify the variables that are changing (volume, temperature, or amount of gas molecules)
• Standard Temperature and Pressure (STP) is 1 atm and 0°C
• Temperature must be in Kelvin (K) for gas law problems, which is obtained by adding 273 to the Celsius temperature

Pressure and Amount of Gas

• Pressure increases when more gas molecules are added to a container because more molecules collide with the container walls, increasing the pressure
• Pressure and amount of gas are directly related
• Besides increasing the amount of gas, two other ways to increase the pressure of a gas are decreasing the volume of the container and increasing the temperature

Temperature and Volume

• The volume of a flexible container increases when the temperature of a gas increases as the pressure remains constant because the gas molecules gain kinetic energy and move faster, occupying more space
• Temperature and volume are directly related
• The volume of a gas can be calculated at different temperatures using the gas laws

Pressure and Volume

• The pressure decreases when the volume of a flexible container is increased and the temperature remains constant because the gas molecules have more space to move, reducing the pressure
• Pressure and volume are inversely related
• The volume of a gas can be calculated at different pressures using the gas laws

Gas Stoichiometry

• 150.0 mL of oxygen at 0.989 atm and 22.0°C can be calculated to find its volume at STP
• The number of moles of a gas can be calculated using the ideal gas law
• The volume of a gas can be calculated using the ideal gas law

Phase Diagrams

• A phase diagram shows the states of matter and phase changes of a substance at different temperatures and pressures
• A triple point graph shows the equilibrium lines of a substance and the states of matter at different temperatures and pressures
• The parts of a phase change diagram include:
  • Solid phase
  • Liquid phase
  • Gas phase
  • Melting point
  • Freezing point
  • Condensation
  • Vaporization
  • Sublimation
  • Deposition
• During the liquid phase, the temperature is increasing
• During vaporization, the substance's temperature remains constant
• Condensation involves a change from gas to liquid
• The region of the graph showing liquid and gas phases existing at equilibrium is called the dew point
• The phase or state of matter at segment CD is liquid
• The temperature labeled T2 is the temperature at which the substance boils
• The region of the graph where molecules have the highest average kinetic energy is the gas phase