Gas Laws

• Matter


  Anything that has mass and volume
• Mass


  The amount of matter contained in an object, usually expressed in grams (g) or kilograms (kg)
• Volume


  The amount of space an object occupies, usually expressed in milliliters (mL) or liters (L)
• Temperature


  The hotness or coldness of a material, can be expressed in Celsius, Kelvin, and Fahrenheit
• Pressure


  Force per unit area, calculated using the formula P = F/A where P is pressure in newtons per square meter, F is force in newtons, and A is area in square meters
• Kinetic Molecular Theory of Gases


  • It is a model used to describe the behavior of gases
  • It explains how macroscopic properties, such as pressure and temperature, are related to the behavior of molecules
  • It is derived from the kinetic molecular theory of matter which describes the three states of matter based on the motion of their atoms
• Gases


  • Composed of molecules that move in constant random motion
  • Gas molecules are not visible to the human eye but the effects of their movements can be detected
• Assumptions of the Kinetic Molecular Theory of Gases

  • Molecules have no definite volume, but they have a definite mass
  • Gas molecules are very small and very far apart from one another, causing them to take the shape of their container
  • Each molecule moves in a straight line until it collides with another molecule or the walls of the container
  • The collision between the molecules is completely elastic
  • There is no attractive force among the molecules or between the molecules and the wall of the container
  • The average kinetic energy of the gas molecules depends only on the temperature of the gas
• Ideal gas


  A gas that follows all the assumptions of the kinetic molecular theory
• Real gas


  A gas that has molecules that occupy space and interact with one another, unlike ideal gases, real gases cannot be compressed indefinitely
• At low pressures, the gas molecules are far apart that the attractive force between them is negligible. Real gases behave as ideally
• At high temperatures, the gas molecules have higher average kinetic energy. They move faster and expand. As a result, they are far apart from one another, making the attractive force between them negligible. At high temperatures, real gases behave ideally
• Gases made up of smaller molecules are more compressible than larger molecules
• At low pressure and high temperature, a real gas behaves like an ideal gas. At high pressure and low temperature, attractive intermolecular forces are no longer negligible, and thus the ideal-gas model no longer applies
• In order for a gas to be ideal, its behavior must follow the Kinetic-Molecular Theory whereas the Non-Ideal Gases will deviate from this theory due to real world conditions
• SI unit for pressure

  Pa (Pascal), 1 Pa = 1 N/m^2, Standard atmospheric pressure = 1 atm = 101,325 Pa
• Boyle's Law


  The pressure (P) and volume (V) of a confined gas are inversely proportional to one another, given that the temperature (T) of the system is held constant
• Boyle's Law


  • Robert Boyle used a J-shaped tube containing mercury and a gas trapped at the close end of the tube which is under constant atmospheric pressure of 1 atm (or 760 torr). He then tried increasing the pressure by another 760 torr by adding 760 mm of Hg. The amount of gas trapped then decreased to about half
• Boyle's Law


  1. Given: V1 = 500 ml, V2 = 450 ml, P1 = 760 torr, P2 = ?

  2. Given: V1 = 0.80 L, V2 = ?, P1 = 1.2 atm, P2 = 6 atm
• Charles's Law


  The temperature (T) and the volume (V) of a confined gas are directly proportional, given that the pressure (P) of the system is held constant. Temperature should always be expressed in Kelvin
• Charles's Law


  • Charles's Law can be demonstrated using hot air balloons. In its deflated form, the balloon contains gas of the same kind as the surrounding air. When the heat source inside the balloon (near the bottom) is ignited, the air will expand, and the balloon will inflate
• Charles's Law


  1. Given: V1 = 600 ml, V2 = ?, T1 = 27 °C or 300.15 K, T2 = 77 °C or 350.15 K

  2. Given: V1 = 100 L, V2 = 120 L, T1 = 25 °C or 298.15 K, T2 = ?
• Gay-Lussac's Law


  The pressure (P) of a given mass of gas is directly proportional with the absolute temperature (T) of the gas, when the volume is kept constant. Temperature should always be expressed in Kelvin
• Gay-Lussac's Law


  1. Given: P1 = 6 atm, P2 = ?, T1 = 27 °C or 300.15 K, T2 = 77 °C or 350.15 K

  2. Given: P1 = 3 atm, P2 = ?, T1 = 25 °C or 298.15 K, T2 = 845 °C or 1118.15 K
• Combined Gas Law


  Given: V1 = 8.33 L, V2 = 5.72 L, P1 = 1.82 atm, P2 = ?, T1 = 286 K, T2 = 355 K
• Ideal Gas Law


  P = absolute pressure in ATM, V = volume in L, n = number of moles of gas, R = universal gas constant of 0.08206 L•atm/mol•K, T = temperature in Kelvin
• Ideal Gas Law


  1. Given: P = 3 atm, V = 6.2 L, n = ?, R = 0.08206 L•atm/mol•K, T = 37 °C or 310.15 K

  2. Given: P = ?, V = 6.65 L, n = 0.80 mol, R = 0.08206 L•atm/mol•K, T = 300 K