Chemistry Unit 2 prt 2

• Gas is fluid
• Gases have mass


  Gas has less density than solid or liquid.
• It is easy to compress gases


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


  Nowhere is there a absence of air. Air is distributed throughout the container. It does not stay grouped in one part of the balloon.
• Different gases can move through each other quite rapidly

  The movement of one substance to another is called diffusion. Gases diffuse easily through each other.
• The pressure of gas depends on its temperature

  The higher the temperature of gas, the higher the pressure. It is a direct relationship.
• Kinetic molecular theory (KMT)- Postulates are only for ideal gases
• 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.
• 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.
• Elastic Collision- No loss of kinetic energy in the system as a result of collisions
• 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


  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.
• 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.
• 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.
• Ideal gas law: pv/nt=R
• STP

  Standard temperature = 0 c

  Standard pressure = 1 atm
• R=Gas constant
• 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
• C to K

  Tof kelvin= T of C + 273
• Pressure vs. number of particles (n)


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

  
• Pressure vs. Number of particles (n)

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

  
• 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)

  
• 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)

  
• 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)

  
• Combined gas law: p1 v1 / t1 = p2 v2 / t2
• Boyle's law: p1 v1= p2 v2
• Charles' law= v1 / t1 = v2 / t2
• Gay Lussac's law: P1 / T1 = P2 / T2
• Gas has no forces of attraction/repulsion
• Absolute zero- The minimum temperature a gas can reach.
• If gas pressure decreases, then the collisions decrease depending on the temperature.