Kinetic Molecular Theory - Answer Keys

 

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  1. What are the postulates of the kinetic molecular theory?

    1.  Particles are assumes to have a V = 0
    2.  Particles are in constant motion
    3.  Particles do not interact (no attraction)
    4.  (KE)avg is directly proportional to temperature

    2.  

     

  2. From this information under what conditions would real gases behave similarly to ideal gases?

    High temperature and low pressure are the conditions that allow a real gas to most closely approximate ideal gas behavior.

    3.  

     

  3. What is the equation for Average Kinetic Energy?

    (KE)avg = 3/2 RT
    1. What does kinetic energy describe?

      The energy of motion.
    2. How does temperature effect kinetic energy?

      The higher the temperature the higher the kinetic energy.

     

     

  4. What is the equation for the root mean square velocity?

                                              μrms = (3RT/M)1/2
    1. How does mass affect the velocity?

      The greater the mass – the slower moving the particle.

    2. How does temperature affect the velocity?

      An increase in temperature results in an increase in velocity.

     

     

  5. Consider:

      6.  

    1. If the plot represents the velocity distribution of 1.0 L of H2 (g) versus 1.0 L of Ar (g) at STP, which plot corresponds to each gas?
       
      Plot A represents Ar (g)
      Plot B represents H2 (g)

      2.  

    2. If the plots correspond to the velocity distribution of 1.0 L of O2 (g) at 273K and 1273K, which plot corresponds to each temperature?

      Plot A represents movement at 273K
      Plot B represents movement at 1273 K.

      3.  

    3. Under which temperature condition would the O2 (g) behave most ideally?

      The higher temperature – 1273 K.

     

     

  6. What is diffusion?

    Diffusion is the movement of a substance from higher concentration to lower concentration.

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  7. What is effusion?

    Effusion is the passage of a gas through a tiny hole into an evacuated chamber.                  

    8.  

     

  8. What is Graham’s Law?

    Compares the rate of effusion of 2 gases.

    Rate of effusion gas1 = (M2)1/2
    Rate of effusion gas2    (M1)1/2

    9.  

     

  9. It took 5.3 minutes for 1.0 L of helium to effuse through a porous barrier.  How long will it take for 1.0L of chlorine gas to effuse under identical conditions?

    22.2 minutes

    10.  

     

  10. Consider the following equations


    How would the following affect number of collisions and length of mean free path?

    1. Increase in mass?

      Fewer collisions.
      No change to length of mean free path.
    2. Increase in diameter of particle?

      More collisions.
      Smaller mean free path.
    3. Increase concentration of gas?

      More collisions.
      Decreased mean free path.

     

     

  11. What is the Van Der Waal’s Equation?

    [Pobserved + a (n/V)2] (V –nb) = nRT
    1. What is it correcting for?

      Pressure is corrected because particles do interact with each other.
      Volume corrected because the actual volume is smaller than ideal volume. 
    2. What does the variable “a” have to do with?

      I always remember this variable by thinking “a” is for attraction.
      The greater the attraction between particles the greater the value of “a”.
    3. What does the variable “b” have to do with?

      I always remember this variable by thinking “b” is for big.
      The larger the particles the greater the value of “b”.

     

     

  12. Would He(g) or H2O(g) have a greater value of “a”?

    H2O

    13.  

     

  13. Would He(g) or Xe(g) have a smaller value of “b”?

    He.

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