SELF TEST UNIT 9 – Thermodynamics and Kinetics 2007

Part I: Matching

            Match the letters in Column B with the numbers in Column A.  Mark the appropriate letters on the Scantron form for the corresponding number.

Column A                                            Column B

1.  exothermic                           a. total energy in a chemical reaction available to do work

2.      endothermic                       b. reaction characterized by release of heat to surroundings

3.   exergonic                            c. measure of a chemical substance’s internal potential energy

4.   endergonic                          d. measure of randomness or disorder of a system

5.   heat capacity                      e. reaction characterized by absorption of heat into the system

6.   calorimetry                         ab. Adding up the energies of components of a reaction produces the total energy change for the reaction.

7.  Gibbs free energy                ac. Study of heat in reactions particularly useful in determining energy content of foods.

8.  enthalpy                               ad. Characterizes a reaction that is spontaneous

9.  entropy                                ae. Characterizes a reaction that is non-spontaneous

10.  Hess’ Law                         bc. A measure of the amount of energy needed to raise the temperature of one gram of a substance by 1oC

Part II: Multiple Choice

            Choose the best answer and fill that letter in on the Scantron sheet by the appropriate number.

11.  Combustion is a common chemical reaction that is used in our lives and in our bodies.  This type of reaction is always:  (a) endothermic.  (b) exothermic.  (c) isothermic.   (d) none of these.

12.  When a reaction has DH < 0,  (a) “H” of the products > “H” of reactants.  (b) the reaction is exothermic.  (c) heat is like a reactant.  (d) all of these.

Use the following equation to answer questions 13-16:

C2H4(g) +  3O2(g)  ŕ 2CO2(g) + 2H2O(g) + 1400 kJ

13.  How much heat is involved in the reaction when 0.10 mol of C2H4 completely reacts?   (a) 1400 kJ  (b) 140 kJ  (c) 14 kJ  (d) 700 kJ

14.  When 280 kJ of heat is produced how many moles of another component would also be involved? (a) 0.30 mol CO2 (b) 0.40 mol H2O  (c) 0.20 mol O2  (d) 5.0 mol C2H4

15.  The above reaction:  (a) would produce heat.  (b) feel cold to the touch.  (c) is non-spontaneous.  (d) has a positive DH.

16.  For the above spontaneous reaction:  (a) DGo > 0.  (b) DGo <0.  (c) DGo = 0. (d) DGo can’t be estimated.

17.  Which of the following correctly relates DHrxn and qsurr in calorimetry problems?
(a) DHrxn = qsurr.  (b) DHrxn = 1/qsurr.  (c) DHrxn = 4.184 qsurr.  (d) DHrxn = — qsurr.

18.  Exothermic reactions are:  (a) always spontaneous.  (b) usually spontaneous. 
(c) usually not spontaneous.  (d) never spontaneous.

19.  Whenever the products have more disorder than the reactants,  (a) DH < 0. 
(b) DH > 0.  (c) DS > 0.  (d) DS < 0.

20.  A reaction is always spontaneous when:  (a) DH is positive and DS is negative.
(b) DH is positive and DS is positive.  (c) DH is negative and DS is negative.
(d) DH is negative and DS is positive.

21.  A reaction is spontaneous at high temperatures and not spontaneous at low temperatures when:  (a) DH is positive and DS is negative.
(b) DH is positive and DS is positive.  (c) DH is negative and DS is negative.
(d) DH is negative and DS is positive.

22.  DG is equal to:  (a) DH + TDS.  (b) DH - TDS.  (c) DS + TDH.  (d) DS - TDH

23.  If DG for a reaction is positive, the reaction:  (a) is not spontaneous.  (b) is spontaneous.  (c) is at equilibrium.  (d) may or may not be spontaneous.

Part III: Problems

24.  When 6.0 g of water are formed according to the equation, how much heat was involved? 
2H2(g) + O2(g) ŕ 2H2O(g)  DH = - 484 kJ

25.  A chemical reaction occurs in calorimeter in an acid solution.  The temperature of 40.0 grams of the water solution increases from 35.5oC to 75.8oC.
  (a) Is the chemical reaction endothermic or exothermic?  Explain.

        (b)  Calculate the heat energy that the water gained. if Cp = 4.184 J/goC.

   (c)  If the chemical reaction took place between 0.50 grams of Mg placed in 40.0 mL of an HCl solution.  Calculate DH  in kJ/mole for this reaction based on this quantity of Magnesium metal.

26.  For a certain change, the value of DH is –28.9 kJ, and the value of DS is +0.355 kJ/K.  Assuming that the temperature is 305 K, calculate the value of DG.  Is the change spontaneous?  Explain why or why not.

27.   Predict whether DS will be negative or positive for the following reactions and explain the reason for your answer.

(a)  CO2(g) ŕ  CO2(s)

(b)  NH3(g)  +  HCl(g) ŕ  NH4Cl(s)

(c)  A beaker of water is warmed from 20oC to 80oC.

28.  For the following reactions, predict the sign of DH, DS and DG.  Explain your prediction.

(a)  Ag+(aq)  +  Cl- (aq) ŕ AgCl(s)  (spontaneous)

(b)  NH4NO3(s)  ŕ  NH4+(aq)  + NO3-(aq)  (reaction occurs and feels cold)

CHECK YOUR ANSWERS