Download Introduction to Entropy - key

AP Chemistry
Entropy Activity
Page 1 of 5
How does the organization of atoms and molecules affect chemical states?
Name:
Key
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Model I: The Deck of Cards analogy
Imagine a brand new deck of cards sitting by itself in a large room. The deck has never been used, except
that it has been removed from its box. It has not been shuffled, but is still in the factory shipped order,
which is:
Hearts, Clubs, Diamonds, Spades
Ace to King within each suit
Definition: The state of a deck of cards refers to the order of cards within the deck. We will call the
factory order an ordered state, that is, the cards from each suit are all together and in order from ace to
king.
Questions
1. In card games, what is the purpose of shuffling the deck before playing?
The purpose of shuffling the deck before playing is to randomized the order of the cards in
the deck.
2. In a randomly shuffled deck of cards
(a) Are there a large number or small number of ordered states?
There are a small number of ordered states in a randomly shuffled deck of
cards.
(b) Are there a large number or small number of disordered states?
There are a large number of disordered states in a randomly shuffled deck of
cards.
3. After shuffling, is the observed order (or state) more likely to be an ordered state, or a disordered
state?
It is more likely that the observed order of the deck will be a disordered state.
4. Form this into a generalization – why does the order of cards in a shuffled deck always come out
disordered? Use a complete sentence.
The process of randomizing the cards by shuffling provides a sequence of cards that are
random in distribution.
5. Are you more or less likely to have ordered states in a blackjack dealers “shoe” – a device that
can contain six or more decks of cards, all shuffled together?
There would be fewer ordered states in a blackjack dealers shoe because there would be
more cards to randomly place at any one position in the deck.
AP Chemistry
Entropy Activity
Page 2 of 5
How does the organization of atoms and molecules affect chemical states?
Information
Entropy (abbreviated “S”) is a measure of the number of states a system can have. However, because the
more states a system can have means that it is more like to be found in a disordered state, we often just
say that entropy is a measure of disorder. (Notice that entropy is related to disorder, not order).
If a change occurs which leads to a more disordered system, the change in entropy (ΔS) is positive. If the
system becomes more ordered, the ΔS is negative.
Questions
6.
Which of these has the highest entropy: an ordered deck or a shuffled deck?
A shuffled deck is more like to be found in a disordered state and, therefore, has the higher
entropy.
7.
Rank the following from least to greatest entropy.
(a) Legos scattered on the floor, legos mixed together in a bucket, legos assembled
together
Least entropy: Legos assembled together; next: Legos mixed in a bucket; most
entropy: Legos scattered on the floor.
(b) A bag of marbles, the same marbles spilled on a floor, the same marbles sitting in a
straight line, the same marbles in a straight line organized by color
Least entropy: marbles organized by color; next: marbles in a straight line;
next: bag of marbles; most entropy: marbles spilled on the floor.
8. If a person spills a bag of marbles, if this a positive or negative change in entropy (ΔS)?
Spilling a bag of marbles is an increase in entropy which means that ∆S is +.
9.
If a person organizes a desk, is this a positive or a negative ΔS (change in entropy) for the desk?
Organizing a desk in a decrease in entropy which means that ∆S is –.
 Model
 Stop;II:
check
your answers
Kessler.
Predicting
the with
SignDr.
of ΔS
AP Chemistry
Entropy Activity
Page 3 of 5
How does the organization of atoms and molecules affect chemical states?
Solid water
Liquid water
Gaseous Water
Definition: For any substance, its state is a description of the position and speeds of the atoms in that
substance.
Questions
10. Draw in representations for the solid, liquid and gaseous water.
11. What do you know about how molecules of H2O can move in a solid versus a liquid versus a gas?
Molecules of H2O move slower in a solid than they do in a liquid; the solid is at a lower
temperature. Molecules of H2O also don’t have as much freedom of movement in a solid as
they do in a gas.
12. In which state of matter, solid, liquid, or gas can the molecules have the most numbers of possible
positions and speeds, in other words, which phase can water have the most chemical states?
Gaseous water has the most chemical states.
13. In terms of entropy, write the phases of matter in proper order from most to least entropic.
gas
>
liquid
>
solid
14. In the transition from liquid to gas, is the system increasing or decreasing in entropy? Is this a
positive or a negative change?
The system is increasing entropy (∆S is +) in the transition from liquid to gas.
15. In the transition from solid to liquid, is the system increasing or decreasing in entropy? Is this a
positive or a negative change?
The system is increasing entropy (∆S is +) in the transition from solid to liquid.
16. Is sublimation (solid to gas) a positive or negative change in entropy?
The system is increasing entropy (∆S is +) in the transition from solid to gas.
AP Chemistry
Entropy Activity
Page 4 of 5
How does the organization of atoms and molecules affect chemical states?
17. If you increase the temperature of a solid, does its entropy increase, decrease or remain the same?
Justify your answer in terms of the definition of chemical state given above.
If you increase the temperature of a solid, the entropy of the solid increases because there is
a wider range of available positions and speeds.
18. If you have a reaction that changes one mole of gas into two moles of gas, will the entropy of the
system increase, decrease or remain the same? Justify your answer in terms of the definition of
chemical state given above.
If you have a reaction that changes one mole of gas into two moles of gas, the entropy of the
system increases because there are twice the number of particles in the system and there is a
wider range of available positions and speeds.
  Stop; check your answers with Dr. Kessler.
AP Chemistry
Entropy Activity
Page 5 of 5
How does the organization of atoms and molecules affect chemical states?
Exercises
1. Fill in the chart below:
Sign of ΔS
Sign of ΔH
Evaporation
+
+
Condensation
–
–
Sublimation (solid to gas)
+
+
Deposition (gas to solid)
–
–
Melting
+
+
Freezing
–
–
Decomposition to atoms
+
+
Formation of a compound
from atoms
–
–
Change
1. A hot piece of metal is dropped into a cool glass of water. What is the sign of ΔS for the metal?
What is the sign of ΔS for the water?
∆Smetal is –. ∆Swater is +.
2. Determine for each of the following reactions if ΔS is positive, negative, or approximately zero.
(a) CaCO3 (s) → CaO (s) + O2 (g)
∆S ~ +
(b) 2 NO2 (g) → N2O4 (g)
∆S ~ –
(c) Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)
∆S ~ 0 or slight +
(d) CF4 (g) + 2 Br2 (l) → CBr4 (l) + 2 F2 (g)
∆S ~ +
(e) KClO4 (s) → KCl (s) + 2 O2 (g)
∆S ~ +
(f) 6 CO2 (g) + 6 H2O (l) → C6H12O6 (s) + 6 O2(g)
∆S ~ –
(g) 2 H2O2 (l) → 2H2O (l) + O2 (g)
∆S ~ +
(h) NaCl (s) + H2O (l) → Na+ (aq) + Cl– (aq)
∆S ~ +
(Solid sodium chloride dissolves in water)