Lycoming College                                                                                                               Write name on back,

Chem 110, 2002                                                Exam II                                                                    upper right

1.   Matching:  match the items in the right column by writing in the CAPITAL letter of a selection from the items in the left. 

      A.   =                                                               _____  T, P 

      B.   LEO                                                                 _____  (S.H.)(m)(DT)

      C.   q + w =                                                             _____  1.00 atm

      D.  DH_rxn  =                                                            _____  P, V

      E.   PV =                                                                _____  GER

      F.   Boyle                                                                _____ 

      G.   q_­cal  =                                                                _____  0.08206 

      H.  760 Torr =                                                        _____  nRT

      I.     =                                                            _____   - 

      J.    Gay-Lussac                                                      _____  

      K.  K  =                                                                 _____   + 273

      L.   R =                                                                   _____ DU

2.   a.   What is the difference between an electrolyte and a non-electrolyte, and how does the Arrhenius theory account for this?

b.       What is the difference between a strong electrolyte and a weak electrolyte.  Cite an example of each, and explain how the Arrhenius theory accounts for the difference.

3.   When aqueous solutions of Hg(NO₃)₂ and NaI are mixed, an orange precipitate forms.  Given that all Na⁺ compounds are soluble, deduce and write balanced molecular, ionic, and net ionic equations representing the observed reaction.

      Molecular:

      Ionic:

      Net Ionic:

4.   Consider the following reaction (unbalanced) that takes place in acidic solution:

            Cr₂O₇^2- _(aq)      +     Cl^1- _(aq)    +     H¹⁺_(aq)      à      Cr³⁺_(aq)    +     Cl_{2 (g)}    +    H₂O

      a.   Assign oxidation numbers to

            each oxygen in Cr₂O₇^{2- -}    _____        

            each chromium in Cr₂O₇^2-                            _____                                       each chromium in Cr³⁺ _____

            each chlorine in Cl^1-            _____          each chlorine in Cl₂           _____

            hydrogen in H¹⁺                       _____          each hydrogen in H₂O      _____

                                                                        each oxygen in H₂O         _____

      b.   In this reaction, which element gets oxidized?_____  Which element gets reduced? ______

Which substance is the oxidizing agent?  ________

c.       Balance the equation

            ___ Cr₂O₇^2- _(aq) +     ___ Cl^1- _(aq)    +     ___H¹⁺_(aq)      à   ___ Cr³⁺_(aq)    +  ___ Cl_{2 (g)}    +   ___H₂O   

5.   If a particular system gives off 643 J of heat and does work equivalent to 246 J, what is its overall DU?

6.   Consider two 5.00 L containers, one holding Cl_2(g) and the other holding CH_4(g), each at the same temperature and pressure.  When compared to the Cl_2, would the CH₄ have a larger, smaller, or same

a.       number of moles of gas? ______________

b.       total mass of gas? _____________

c.       average translational kinetic energy? ____________

d.       average molecular speed? _____________

                Calculate below the numerical value for this relative rate of diffusion of CH₄ compared to Cl₂:

      e.   If the temperature of either container were increased, and the volume could expand or contract so as to keep pressure constant, what would happen to the volume of the gas in that container, and WHY?  Explain in terms of kinetic-molecular theory.

7.   If 2.4 L of gas at 740 Torr is increased to 5.6 L while its temperature is increased from 100  to 200 , what would be the new pressure of the gas?

8.   A piece of unknown metal having a mass of 15.3 g is taken from an oven at 116 ºC and immersed in 95.5 mL of water (S.H. = 4.184 J g^-1 ºC^-1;  d = 1.00 g/mL) at 23.9 ºC in a calorimeter cup.  The water temperature rises and levels off at 42.4 ºC.  What is the specific heat of the metal?

9.   In a lab experiment, 2.72 g of a metal reacts with excess hydrochloric acid to produce hydrogen gas, H2.

      a.   If 1,040 mL of hydrogen are collected by water displacement at a barometric pressure of 761 Torr and a temperature of 23 °C, calculate the moles of H2 collected. 

                              (Vapor pressure of water at 23 °C = 21 Torr)

      b.   Given that 2.75 g of metal were reacted, calculate the molar mass of the metal, assuming the reaction followed this equation:   M(s)   +   2 HCl(aq)  à  H₂(g)   +   MCl₂(aq)         

10.  Consider the following reaction:

                              5 C _(s)    +    2 SO_{2 (g)}      à     CS_{2 (l)}   +    4 CO _(g)           DH  =  ?

      a.   Given the information below, calculate DH for the reaction as written.

.

      b.   Based on your answer to 10.a., is the reaction endothermic or exothermic? ___________

      c.   Based on your answer to 10.a., how much heat is involved in the reaction of 30.0 g of carbon with sufficient SO₂?

11.   Determine the enthalpy change for the oxidation of ammonia:

                        4  NH3    +    5  O2    4  NO    +    6  H2O          DH  =  ?

      from the following data:

                        N2        +     O2    2 NO                                     DH  =  + 180.5 kJ

                        N2        +   3 H2    2 NH3                                   DH  =  –   99.2 kJ

                        2  H2    +      O2    2  H2O                                  DH  =  – 571.6 kJ