Chemistry Unit 2 prt 2

• Gases have mass


  More air increases mass.

  Gas has less density than solids or liquids
• It is easy to compress gases


  When squeezing gas, the volume will be reduced
• Gases fill their containers completely 


  Nowhere is there an absence of air. Air is distributed throughout the space and is not grouped in only one part.
• Different gases can move through each other quite rapidly


  Gases diffuse easily through each other. Ex: Smelling food outside your room
• The pressure of gas depends on its temperature 


  The higher the temperature of gas the higher the pressure.

  The lower the temperature of gas the lower the pressure
• Gas properties are explained by a kinetic-molecular model that describes the behavior of the submicroscopic particles that make up a gas.
• Kinetic Molecular Theory (KMT)

  1. A gas consists of very small particles (atoms or molecules), each of which has mass
  2. The distance separating gas particles are relatively large.
  3. Gas particles are always in constant, rapid, and random motion
  4. Collisions of gas particles occur with each other or with walls of elastic
  5. The average kinetic energy of gas particles depends only on the temperature of gas.
  6. Gas particles extert no force on one another.
• Postulate 1 of KMT: A gas consists of very small particles (atoms or molecules) each of which has mass.
• Postulate 2 of KMT: The distance between gas particles are relatively large compared to the size of individual particles.
• Postulate 3 of KMT: Gas particles are always in constant, rapid, and random motion.
• Elastic Collision


  No loss of kinetic energy in the system as a result of collisions
• Postulate 4 of KMT: Collisions of particles occur with each other or with walls of elastic. Exert pressure on containers caused by collisions of particles.
• Postulate 5 of KMT: The average kinetic energy of gas particles depends only on the temperature of gas. Gas particles have a higher kinetic energy at a higher temperature. Gas particles have a lower kinetic energy at a lower temperature. (No intermolecular forces)
• Postulate 6 of KMT: Gas particles exert no force on one another. Attentive forces between gas particles are so weak that the model assumes them to be zero. Gas particles do not slow down and condense into liquid because they exert only very weak attractive forces upon each other.
• The 4 measurable quantities to describe a gas

  1. Amount of gas particles (n)
  2. Volume (mL, L, or Cm^3)
  3. Temperature (kelvin/K)
  4. Pressure (torr, atm, psi, mmHg, Pascal, Kpascal)
• Pressure is defined as the amount of force acting on an object per unit area. It can also be thought of as the weight of air above a certain point.
• Pressure

  Every time a particle collides with a wall, it exerts an outward force on the wall. The outward force spread over the area of the container is pressure.
• Gas is heated > particles move faster > gas will collide with walls more >exert more pressure
• What instrument is used to measure atmospheric pressure? 


  Barometer
• How does the atmosphere exert pressure?

  The air has mass and is attracted by Earth's gravity. The force of the air attraction to gravity produces force.
• Temperature conversion

  • Energy of gas particles depends on their temperature
  • Temperature of gas is usually measured with a thermometer marked in degree celsius
  • ALL temperature involving gas must be converted from celsius to kelvin
  • Kelvin temperature scale has NO negative temperatures
• Kelvin

  • ALL temperature involving gas must be converted from celsius to kelvin
  • Kelvin temperature scale has NO negative temperatures
  • Kelvin scale is used in gas law problems because pressure and volume of a gas depend on the kinetic energy or motion of particles
  • The kelvin scale is proportional to KE of the particles, 0 K (absolute zero) means ZERO kinetic energy
  • In theory, absolute zero means no particles move
  • 0 K is the lowest possible energy state
  • 0 degree C does not mean that the KE of particles is 0, it is simply the freezing temperature of water
• Temperature conversion for C to Kelvin

  Tof kelvin= T of C + 273
• Pressure vs. Number of Particles

  With more particles there will be more collisions and a greater pressure.

  
• Pressure vs. Number of particles

  With more particles there will be more collisions and a greater pressure.

  
• $p^1$= Starting pressure

  $p^2$=Final pressure

  $v^1$=Starting volume

  $v^2$=final volume
• Pressure vs. Temperature (Gay Lussac)

  • Temperature and pressure at a constant volume and number of particles
  • Temperature must be in Kelvin
  • Law= T^ P^
  • As temperature increases, pressure increases. As temperature decreases, pressure decreases. (Direct relationship)
  • Formula: $p^1/t^1=$$p^2/t^2$

  
• Volume vs. Temperature (Charles law)

  • Relates temperature and volume at a constant pressure and number of particles
  • Temperature must be in kelvin
  • Absolute zero is theoretically minimum temperature that a gas can reach
  • Law= T^ V^
  • As temperature increases, volume increases (direct relationship)
  • Formula: $v^1/t^1=$$v^2/t^2$

  
• Pressure vs. Volume (Boyle's law)

  • Relates pressure and volume at a constant temperature and number of gas particles.
  • Law= P^ V
  • As pressure increases, volume decreases As volume increases, pressure decrease (Inverse relationship)
  • Formula: $p^1 v^1 =$$p^2 v^2$

  
• Boyle's law formula: $p^1 v^1 =$$p^2 v^2$

  Need: Pressure and volume
• Gay Lussac's law formula: $p^1/t^1=$$p^2/t^2$

  Need: Pressure and Temperature
• Charles' Law formula: $v^1/t^1=$$v^2/t^2$

  Need: Volume and temperature
• Combined gas law: $p^1 v^1/t^1=$$p^2 v^2/t^2$
• R=Gas constant
• STP


  Standard temperature = 0 c

  Standard pressure = 1 atm
• Ideal gas law: $pv/nt=$$R$