1. Entropy

2. Definition of Entropy
Entropy is a measure of the disorder of a substance.
Low entropy: highly ordered (crystalline solid)
Low entropy: low temperatures
High entropy: high temperature, gases

3. Examples of High Entropy
Gases have more entropy than liquids and solids
Mixtures (solutions) more than pure substances
Chemical changes that lead to more moles of products than reactants
Chemical changes that produce moles of gases – especially explosions!

4. TNT

5. Why is entropy important?
Processes that lead to lower energy (exothermic) are more likely to happen in our universe.
Endothermic processes can also happen spontaneously if they lead to higher levels of disorder (entropy)
Examples:
- ice melts above 273 K
- KNO3 dissolves even though the ions absorb energy from the water

6. Which sample has the lowest entropy?
1 mole of KNO3(l)
1 mole of KNO3(s)
1 mole of H2O(l)
1 mole of H2O(g)

7. In terms of energy and entropy, systems in nature tend to undergo changes toward
higher energy and higher entropy
higher energy and lower entropy
lower energy and higher entropy
lower energy and lower entropy

8. A reaction must be spontaneous if it is
exothermic and there is an increase in entropy
exothermic and there is a decrease in entropy
endothermic and there is an increase in entropy
endothermic and there is a decrease in entropy

9. Which 10-milliliter sample of water has the greatest degree of disorder?
H2O(g) at 120°C
H2O() at 80°C
H2O() at 20°C
H2O(s) at 0°C

10. Which list of the phases of H2O is arranged in order of increasing entropy?
ice, steam, and liquid water
ice, liquid water, and steam
steam, liquid water, and ice
steam, ice, and liquid water

11. Given the change of phase: CO2(g) → CO2(s) As CO2(g) changes to CO2(s), the entropy of the system
decreases
increases
remains the same

12. Which process is accompanied by a decrease in entropy?
boiling of water
condensing of water vapor
subliming of iodine
melting of ice

13. Which of these changes produces the greatest increase in entropy?
CaCO3(s) → CaO(s) + CO2(g)
2 Mg(s) + O2(g) → 2 MgO(s)
H2O(g) → H2O(l)
CO2(g) → CO2(s)

22. What is the activation energy for the catalyzed reaction in the forward direction?
What is the activation energy for the uncatalyzed reaction in the reverse direction?
What is the potential energy of the products?