1. Chem in a ZipLoc Post-Lab Questions

2. Question #1
PHYSICAL CHANGES
CHEMICAL CHANGES
Color Change
Gas production
Temperature change (either hot or cold)
New odor
Dissolving

3. Gas is trapped in the bag Vs. candle demo
Question #2
Imagine that you had measured the total mass of the bag (reactants and contents) prior to mixing. Would you expect the overall mass to increase, decrease, or remain the same after the reaction is complete?
STAY THE SAME!
Gas is trapped in the bag
Vs. candle demo

4. Question #3 Cl2, H2, O2, CO2 Will go out DEADLY (mustard gas) explode
What gas do you think was being produced inside the bag? The reactants were Baking Soda (NaHCO3) and calcium chloride (CaCl2). Can you think of a diagnostic test that could be used to determine the identity of the gas?
Cl2, H2, O2, CO2
Will go out
DEADLY (mustard gas)
explode
burn brighter and larger

5. Question #4 Baking soda → COLD Calcium Chloride → HOT EXO → outside
Did either reaction feel hot or cold? Which one? What does the prefix exo and endo mean?
Baking soda → COLD
Calcium Chloride → HOT
EXO → outside
ENDO → inside

6. Thermochem Notes #2: Exo/Endo & Entropy
WCHS Chemistry

7. System vs. Surroundings
System - The chemicals or reaction
Surroundings - the container and everything else outside of the system.
***** Be careful in your explanations!! → What you state as system vs. surroundings affects your answer!

8. Reaction or Process Exothermic Releases energy in the form of heat
Be careful! May not always feel hot!
Examples:
Fire

9. Exothermic Reaction or Process
LOSS OF ENERGY
Reactants have more energy than products (lose energy)

10. Reaction or Process Endothermic Absorbs energy from the surroundings
Be careful! May not always feel “cold”!
Examples:
Baking soda in water
Ice pack

11. Endothermic Reaction or Process
ADDITION OF ENERGY
Products have more energy than reactants (gain energy)

12. Entropy “Disorder” Measure of the randomness/disorder of a system
The more disordered, the greater the entropy
Symbol for Entropy = S
Ex → If your room is very messy = very disordered = large amount of entropy

13. Entropy Levels
CRYSTAL
SOLID
LIQUID
AQUEOUS SOLUTION
GAS
LOW ENTROPY
HIGH ENTROPY
Nature tends to favor reactions/processes that have MORE ENTROPY! (=are more disordered)
“Spontaneous” → A process that occurs without any ongoing outside intervention.

14. Examples of Spontaneous Processes
Burning a Candle
Energy is released so…
EXOTHERMIC
INCREASING ENTROPY
AND becoming more disordered, so…
CRYSTAL
SOLID
LIQUID
AQUEOUS SOLUTION
GAS
Ice cube melting
Energy is absorbed →
ENDOTHERMIC
INCREASING ENTROPY
BUT → becoming more disordered so

15. INCREASE IN ENTROPY (more disordered)
Spontaneity
Two factors that contribute to spontaneity:
EXOTHERMIC PROCESS
INCREASE IN ENTROPY (more disordered)
Sometimes they work together, but sometimes they don’t!

16. Heat Pack Example
Why is the process that the heat pack (NaC2H3O2) goes through considered spontaneous?
NaC2H3O2(l) → NaC2H3O2(s)
Energy is released, so…
EXOTHERMIC
DECREASING ENTROPY
Becoming less disordered, so…
CRYSTAL
SOLID
LIQUID
AQUEOUS SOLUTION
GAS

17. Ammonium Nitrate Example
We put solid Ammonium Nitrate (NH4NO3) in water, and it dissolved (= spontaneous)
NH4NO3(s) → NH4NO3(aq)
Energy is absorbed so…
ENDOTHERMIC
INCREASING ENTROPY
Becoming more disordered so…
CRYSTAL
SOLID
LIQUID
AQUEOUS SOLUTION
GAS

18. Freezing Water How about putting liquid water in the freezer?
H2O(l) → H2O(s)
Becoming less disordered so…
DECREASING ENTROPY
Energy is released, so…
EXOTHERMIC