THERMODYNAMICS

MARILYN L. MAYFIELD            LINDBLOOM TECH. H.S.
                               6130 S. WOLCOTT
                               CHICAGO, IL 60636
                               1-312-471-8700

BEHAVIORAL OBJECTIVES:
     THE STUDENTS SHOULD BE ABLE TO DEFINE AND GIVE AN EXAMPLE OF: AN ENDOTHERMIC 
AND AN EXOTHERMIC REACTION; ENTROPY AND THE EFFECTS OF ITS INCREASE; FREE ENERGY 
AND THE EFFECTS OF ITS CHANGE BEING NEGATIVE, POSITIVE, OR NEUTRAL. 
 
MATERIALS:
    1. TWO ROUND BOTTOM FLASKS WITH TWO SOLID STOPPERS AND TWO ONE-HOLED 
STOPPERS CONNECTED BY A SHORT PIECE OF HOLLOW GLASS TUBING; CONCENTRATED AMMONIA 
WATER; UNIVERSAL INDICATOR PAPER OR RED LITMUS PAPER. 
    2. .1 MOLE EACH OF: AMMONIUM NITRATE, SODIUM HYDROXIDE, SUCROSE, AND LITHIUM 
ACETATE; 10ML GRADUATED CYLINDER; FOUR TEST TUBES; THERMOMETER. 
    3. STRIPS OF ZN AND CU; SOLUTIONS OF ZINC SULFATE AND COPPER SULFATE; TWO 
BEAKERS. 
    4. A SET FOR EVERY TWO OR THREE STUDENTS OF: 3.2 GRAMS OF BARIUM HYDROXIDE 
HYDRATE; 1.7 AMMONIUM NITRATE; ONE TEST TUBE WITH STOPPER; SMALL BEAKER; STRIP OF 
INDICATOR PAPER. 
  
STRATEGIES:
    1. MOISTEN INDICATOR PAPER AND STICK TO THE BOTTOM OF BOTH FLASKS. ADD A FEW 
DROPS OF AMMONIA TO ONE FLASK THEN TEST THE VAPOR WITH A MOISTENED STRIP OF PAPER. 
ATTACH THE FLASKS TO RING STANDS, CONNECT THEM WITH THE STOPPER AND TUBE ASSEMBLY 
AND ALLOW AMMONIA TO DIFFUSE WHILE THE NEXT PART IS DONE. STUDENTS REPORT ANY 
CHANGE OBSERVED. 
    2. HAVE A STUDENT ASSISTANT RECORD THE TEMPERATURE CHANGE AS EACH SUBSTANCE 
DISSOLVES. ALL TEMPERATURES INCREASE OR DECREASE IN DISSOLVING EXCEPT LITHIUM 
ACETATE WHICH STAYS THE SAME. THIS LEADS TO A DISCUSSION OF THE DISSOLVING 
PROCESSES WHICH ARE RESPONSIBLE FOR THE CHANGES. 
    3. THE EQUATIONS ARE WRITTEN ON THE BOARD AND THE CORRESPONDING MATERIALS 
MIXED IN BEAKERS FOR: 
    COPPER + ZINC SULFATE  AND  ZINC + COPPER SULFATE
AFTER THE HANDS-ON PART STUDENTS OBSERVE BEAKERS AND COMPLETE THE EQUATIONS. 
    4. THE STUDENTS ARE GIVEN TWO SEPARATE CONTAINERS OF SOLIDS LABELED #1 AND #2. 
WHEN TOLD TO, THEY MIX THEM, STOPPER, SHAKE AND OBSERVE. IN ONE OR TWO MINUTES THE 
TEST TUBE GETS VERY COLD. THEY ARE TOLD TO TEST FOR GAS AS I DID WITH THE PAPER TO 
SEE IF AMMONIA IS PRESENT. 
    5. AFTER THE HANDS-ON PART ALL OBSERVATIONS ARE DISCUSSED. THEY EXPECT THE 
AMMONIA TO DIFFUSE. WHEN WE GET TO THE EQUATION FOR THE FREE ENERGY CHANGE WE USE 
THIS AS AN EXAMPLE FOR SPONTANEOUS CHANGES BEING ASSOCIATED WITH AN INCREASE IN 
ENTROPY. 
    THE DIFFERENT TEMPERATURE CHANGES IN DISSOLVING ALLOWS FOR A THOROUGH 
DISCUSSION OF THE ENERGY INVOLVED IN BONDS FORMING AND BREAKING. 
    THE FACT THAT AN EQUATION COULD BE WRITTEN FOR A REACTION THAT DID NOT OCCUR 
CONVEYS THE IDEA THAT THERE MUST BE A "DRIVING FORCE". 
    THE EXTREME DECREASE IN TEMPERATURE AND FORMATION OF A LIQUID {WATER} AND A 
GAS FROM TWO SOLIDS LEADS TO THE QUESTION OF WHY REACTIONS OCCUR AS THEY DO. 
    THE EQUATION : FREE ENERGY CHANGE = ENTHALPY CHANGE - TEMPERATURE [ENTROPY 
CHANGE] IS INTRODUCED, ENTHALPY AND ENTROPY ARE DISCUSSED FROM THE PREVIOUS 
OBSERVATIONS IN ORDER TO EXPLAIN THE EQUATION. 
    THE HANDS-ON IS A BEAUTIFUL EXAMPLE OF HOW THIS WORKS. IN ORDER FOR THE 
REACTION TO BE SPONTANEOUS THE CHANGE IN FREE ENERGY MUST BE NEGATIVE. EVEN THOUGH 
2
THE CHANGE IN ENTHALPY IS POSITIVE, THE INCREASE IN # MOLES AND THE CHANGES FROM 
SOLID TO LIQUID AND GAS MAKES SUCH A LARGE INCREASE IN ENTROPY THAT THE 
TEMPERATURE [ENTROPY CHANGE] TERM PREDOMINATES AND THE CHANGE IN FREE ENERGY IS 
NEGATIVE MAKING THE REACTION SPONTANEOUS. 
    INFORMATION FROM THE STANDARD HEAT OF FORMATION AND ENTROPY TABLES ARE USED TO 
CALCULATE THE CHANGE IN FREE ENERGY VALUE.