CHEM125                                                                                                      Fall, 2003

Hourly Exam # 4                                                                                             Dunnivant

 

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I have neither given nor received aid on this exam.  

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R = 0.08206 L-atm/K-mol

PV=nRT

Molecular weights:      Na = 22.99      N = 14.00       

Specific heat of water = 4.184 J/gK

q = specific heat * grams * DK

heat of evaporation for water = 40.7 kJ/mol

 

NOTES:

Show all work for partial credit.   Significant figures will be graded throughout the exam.

 

  1. (10 pts) Rank the following in terms of increasing strength.

 

Ion-dipole                          Induced dipole-induced dipole

Hydrogen bonding            Dipole-dipole

Induced dipole-dipole

 

Low intermolecular strength

 

 


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High intermolecular strength

 

 

 

  1. You have a beaker of water that you want to cool by evaporating some of the water.  (a) (8 pts) If you evaporate 100 g of the water by blowing dry He gas through it, how much energy is removed?

 

 

      (b) (8 pts) How many grams of water can you cool from 50 to 30 degrees C using the energy you removed in part a?  Show all work for partial credit including equations.

 

 

      ( c) (4 pts) Where does the energy come from to evaporate the water in part a?

 

 

  1. (5 pts) Explain the difference between intermolecular and intramolecular forces.

 

 

  1. (5 pts) Name the two intermolecular forces involved in the following:

 

dissolving NaCl in water   ______________________________

 

 

dissolving O2 in water _____________________________

 

 

in liquid I2   __________________________________

 

 

between DDT (a non-polar pesticide) and water ______________________

 

 

between DDT and lipid deposits in our bodies  ______________________

 

 

  1. (15pts) Sodium azide is used to rapidly create gas to fill the air bags in your cars.  Using the following reaction, determine how much (grams) NaN3(s) is needed to fill the air bag if 32.0 L of N2 is needed.  Show all work and setup of the problem for partial credit.  Assume 25.0oC and 1.00 atm total of pressure.

 

NaN3(s)  ˆ  Na(s)  + N2(g)

 

 

  1. (5 pts) Using kinetic molecular theory, explain the origin of pressure in a filled balloon.  (Exactly where does the force in the pressure come from?)

 

 

  1. (5 pts) Explain the difference between diffusion and effusion.

 

 

 

  1. (10 pts) Using the following figure (IGNORE Ethylene Glycol for ALL questions):

 

File written by Adobe Photoshop¨ 4.0
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


a)     which compound has the strongest intermolecular forces?

 

                

 

b)    which compounds can undergo hydrogen bonding?

 

 

 

(c )  at what pressure will each compound boil?

 

(d)  what could you do to lower the boiling point?

 

(e)   what does each line represent?

 

 

  1. (5 pts) Explain the difference between cohesive and adhesive forces.

 

  1. (5 pts) Explain how surfactants lower the surface tension of water.  Feel free to make a drawing.

 

  1. (10 pts)  Using the figure on the following page, answer the following:

a)     What does the line from A to D represent?

b)    If you are at point B, and apply pressure, what phase of H2O will you create?

c)     Where does sublimation occur?