CHEM_100                                                                            2012

 

 

 

ASSIGNMENT # 2                Due to October 31

 

 

REDOX REACTIONS and THERMOCHEMISTRY

 

 

 

  1. {10} Rules for Assigning an Oxidation Number (O.N.). Complete the table

 

1. For an atom in its elemental form (Na, O2 etc.): O.N. = 

 

2. For a monoatomic ion (i.e., Fe3+):                                    O.N. =

 

3. For Group 1A (1) in all compounds                                O.N. =  

 

4. For Group 2A (2) in all compounds                                O.N.=

 

5. For hydrogen in combination with nonmetals                O.N. =

 

                           in combination with metals                        O.N.=  

 

6. For fluorine in all compounds                                          O.N. =

7. For oxygen in peroxides                                                   O.N.=

 

                        in all other compounds (except with F)       O.N.=

 

8. For group 7A (17) in combination with metals,

 nonmetals (except with O), and other halogens

 lower in the group                                                                O.N.=

 

 

  1. {10} Identify oxidation number for N and S in the following:

(a)        NO3-          b) NO2-       c) NH3               d)  N2O5                e)NO            f)NO2   

(g) N2O3                h) S8             i) SO42-

 

 

 

  1. {10} Identify the oxidizing agent (the one which is taking electrons)  and reducing agent (the one which is loosing electrons) in each of the following:

 

(a) 2Al (s) + 3 H2SO4 (aq) à Al2(SO4)3(aq) + 3 H2 (g)

 (b) PbO (s) + CO(g) à Pb (s) + CO2 (g)

 (c) 2H2 (g) + O2 (g) à 2H2O (g)

(d) 5CO(g) + I2O5 (s) à I2 (s) + 5 CO2 (g)

 (e) 2Na (s) + 2H2O (l) à 2NaOH (aq)  + H2 (g)

 

  1. {20} Balance the following equations using the method of half-reactions (9 scores). Identify the oxidizing and reducing agents (1 score). Show your work!

(a)  SO32-(aq)  +  MnO4- (aq)  à SO42- (aq)  +   Mn2+ (aq)     (acidic solution)

                       

(b) MnO4- (aq)  +  Br- (aq)  à  MnO2 (s)  +  BrO3-(aq)  (basic solution)

  

 

THERMOCHEMISTRY

5. {10} When 1 mole of nitroglycerine decomposes, it causes a violent explosion and releases 5.72 x103 kJ of heat.

C3H5(NO3 )3 (l) à 3 CO2(g)  +  5/2 H2O (g)  +1/4O2(g)    + 3/2 N2 (g)

(a)   {2} Is the reaction exothermic or endothermic? Write a thermochemical equation (ΔH should be included).

(b)   {3} Draw an enthalpy diagram for it.

(c)    {5} How much heat will be released when 1kg of nitroglycerine decomposes?

  1. {5} For which system ΔE is always negative?

(a)               absorbs heat and does work

(b)               gives off heat and does work

(c)                absorbs heat and has work done on it

(d)               gives off heat  and has work done on it

 

  1. {5} Of the following, which one is not a state function?

(a)   H

(b)   E

(c)    q

(d)   T

(e)    P

 

Hess’s Law

  1.  {10} Calculate the enthalpy of the rxn:

N2 + 2O2     à  2NO2

Using the following data:

2NO à N2   +   O2       ΔH = -180 kJ

2NO + O2 à 2NO2                ΔH = -112 kJ

 

 

9.  {20}. Determine the enthalpy change for the oxidation of ammonia:

4NH3 (g)   +  5 O2 (g)  à  4 NO(g)   + 6 H2O(g)          ΔH = ???

 

from the following data:

 

N2 (g)   + 3 H2 (g) à  2 NH3 (g)       ΔH = -99.22 kJ

N2 (g)   + O2 (g) à  2 NO (g)       ΔH = +180.5 kJ

2H2 (g)   + O2 (g) à  2 H2O (l)       ΔH = -571.6 kJ

H2O (g)  à H2O (l)                            ΔH = -44.01 kJ

 

(hint: watch for physical state of water!}