Ombey

• Gas


  • One of the four fundamental states of matter (the others being solid, liquid, and plasma)
  • A fluid (such as air) that has neither independent shape nor volume but tends to expand indefinitely
• Properties of Gases


  • A gas is highly compressible
  • A gas expands as temperature increases
  • A gas flows easily
  • A gas has lower density than solids and liquids
  • Gases are miscible
• Kinetic Molecular Theory of Gases

  • Developed by Rudolf Clausius, James Maxwell, and Ludwig Boltzmann
  • Helps us to understand the behavior of gases at the molecular level
• Kinetic Molecular Theory of Gases

  1. A gas consists of very small particles

  2. The particles are in constant, random, straight-line motion

  3. The gas particles are separated by distances much larger than their size

  4. The attractive forces between particles are negligible, and the particles act independently of one another

  5. The gas particles collide with each other and with the walls of the container in a perfectly elastic manner

  6. The average kinetic energy of the gas particles is proportional to the absolute temperature (kelvin)
• The particles of gas move at an average speed of around 500 m/s at standard conditions. These particles undergo more than a billion collisions every second, and the average distance between collisions is approximately 5x10-8 m or 0.00000005 m.
• Pressure (P)


  • Defined as force per unit area
  • Pressure is the result of the collision of gas particles with the walls of the container

  
• Units of Pressure

  • Pascal (Pa)
  • millimeter mercury (mmHg)
  • atmosphere (atm)
  • pounds per square inch (psi)
  • torr

  
• 101,325 Pa = 1 atm = 760 mmHg = 760 torr = 14.7 psi
• Atmospheric Pressure


  • The pressure exerted by the gas molecules in the air
  • The average atmospheric pressure at sea level is also called standard atmospheric pressure with a value of 1 atmosphere (1 atm)
• Practice Math: Converting Pressure Units

  472 mmHg = ? atm, Pa, torr
• Temperature (T)


  • The SI unit for temperature is Kelvin (K) and known as the absolute temperature scale
  • The kelvin scale was proposed by William Thomson, an English physicist also known as Lord Kelvin
  • The absolute temperature scale is 0 K although no one has created such conditions. It is predicted that all particles will stop from moving and will exert zero pressure at the said temperature.

  
• Temperature Conversion Formulas

  1. K = °C + 273.15

  2. °C = (°F – 32) / 1.8

  3. °F = 1.8 (°C) + 32
• Temperature is the measure of the kinetic energy of the gas particles.
• Standard Temperature and Pressure (STP)

  Standard Temperature = 0 °C

  Standard Pressure = 1 atm
• Practice Math: Converting Temperature to Kelvin

  87 °C

  330 °F
• Volume (V)


  • Defined as the space occupied by the gas particles
  • The volume of the gas is equal to the volume of the container in which the gas is placed
• Units of Volume


  • liters (L)

  milliliters (mL)

  m3

  cm3

  ft3
• Amount of Gas


  • The addition of gas increases the amount of gas in a container and the pressure inside it becomes higher
  • The usual way of measuring the amount of gas is by mass (grams)
  • The mass of the gas in grams must be changed to moles (n)
• Practice Math: Calculating Moles of Gas

  88.0 g CO2

  22.0 G H2

  13.6 g NH3
• Gas Laws


  Relationships between pressure, volume and temperature of a sample of gas

  
• Boyle's Law


  Pressure is inversely proportional to volume such that, when pressure is doubled, the volume of the gas decreases to half its original value

  
• Boyle's Law states that: For a given amount of any gas (n)and with temperature (T) held constant, the volume of the gas varies inversely with pressure.

  
• Boyle's Law Sample Problems

  A sample of nitrogen gas (N2) has a volume of 12 L and a pressure of 760 mmHg. When the gas is released, it gives 32 L of nitrogen. If the temperature is the same, what is the new pressure of nitrogen?

  A gas tank holds 20 L of oxygen (O2) at a pressure of 15 atm. How many liters will the gas occupy if the pressure is changed to 0.800 atm at constant temperature?

  
• Practice Math: Boyle's Law

  A sample of methane (CH4) has a volume of 75 mL at a pressure of 0.90 atm. What is the volume of the gas at each of the following pressures if there is no change in temperature?

  0.45 atm

  520 mmHg

  
• Charles' Law


  At constant pressure and amount of gas, the volume of a gas increases with every increase in temperature. Also, volume decreases as temperature decreases.

  
• Real Life Applications of Charles' Law

  • Hot Air Balloon

  Dented Ping-Pong balls back to normal shape

  Air inside tires while travelling

  Jogging during cold mornings

  Baking breads and cakes

  Gasoline-powered automobiles
• Charles' Law Sample Problems

  An inflated balloon with a volume of 0.75 L at 30°C was placed inside the freezer where temperature is -10°C. Find out what will happen to the volume of the balloon if the pressure remains constant.

  A cylinder with a movable piston contains 250 cm3 air at 10°C. If the pressure is kept constant, at what temperature would you expect the volume to be 150 cm3?

  
• Gay-Lussac's Law


  At constant volume and amount of gas, the pressure of the gas is directly proportional to its temperature.

  
• Real-life Applications of Gay-Lussac's Law

  • Firing a bullet

  Pressure Cooker
• Gay-Lussac's Law Sample Problems

  A certain light bulb containing argon has a pressure of 1.20 atm at 18°C. If it will be heated to 85°C at a constant volume, what will be the resulting pressure?

  At 20°C a confined ammonia gas has a pressure of 2.50 atm. At what temperature would its pressure be equal to 760 mmHg?

  The helium tank has a pressure of 650 torr at 25°C. What will be the pressure if the temperature is tripled?

  
• Combined Gas Law


  • Combination of Boyle's and Charles' Laws which describes the pressure-volume-temperature relationships of a constant amount of gas
  • Useful for studying the effect of the changes in two of the variables – pressure, volume, or temperature – on the third as long as the amount of gas remains the same

  
• Combined Gas Law Sample Problem

  A 20.0 mL bubble is released from a tank at a pressure of 4.00 atm and a temperature of 10.0°C. What will be the volume of the bubble when it reaches the water surface, where the pressure is 1.00atm and the temperature is 19°C?

  
• Real Life Applications of Combined Gas Law

  • Storage of gas tanks in cool places

  Avoiding spray cans containing volatile substances to flames

  Proper disposal of containers of volatile substances

  The increase of air volume and pressure in automobile tires when travelling long distances