1111Spontaneous Process• A process is spontaneous if it occurs

without outside intervention, it happens on its own.

• Spontaneous processes can be fast or slow!

• Examples of Spontaneous Processes:–a ball rolls downhill, but the ball never

spontaneously rolls uphill–steel rusts, but the rust never spontaneously

forms iron and oxygen

–Water spontaneously freezes at temperatures below 0o C

2222Entropy, SEntropy, S• ENTROPY (S) is a measurement of

the change in RANDOMNESS or DISORDER of the particles in a chemical reaction.

• Spontaneous reactions will always move toward an increase in Entropy (Increase in randomness) Why is this?

• Because things are more likely to occur in a random order than in an organized arranged order.

33332nd Law of 2nd Law of

ThermodynamicsThermodynamics• The second law states that the disorder in The second law states that the disorder in

the universe is always increasing. As the universe is always increasing. As disorder increasing, energy is transferred disorder increasing, energy is transferred to less usable forms. So…

• If ∆S > 0, entropy is increasing, the particles are becoming more chaotic.

• If ∆S < 0, entropy is decreasing, the particles are becoming more organized.

4444Which is more likely? • Which kind of card hand are you more

likely to be dealt?

Random cards Or a Royal Flush

• It is more likely that you will get a collection of random cards rather than an ordered hand.

5555Probability of Disorder• If you never clean your room, will your

stuff become more organized or more chaotic?

• This is the natural progression in the universe!

• If there is no outside force, Entropy will increase!

6666Factors that affect Entropy• There are several factors that determine the

randomness or disorder of compounds and molecules.

• 1) States of Matter / Temperature

• 2) Atom and Molecular Complexity

• 3) Amount of a compound

• 4) Mixing Compounds

• Think about situations that have the greatest amount of particle movement.

• An increase in movement is an indicator for increased entropy and more randomness!!!

7777State of Matter• Solids have the least entropy due to a more

organized and structured shape.

• Gases have the greatest entropy due to an undefined shape and lots of kinetic energy.

• Ssolid < Sliquid << Sgas

• Increase temperature, Increase Entropy.

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• Entropy increases when you increase atomic complexity

• Increases in the number of protons, electrons, neutrons, increases entropy.

- Increase in molecular complexity generally leads to increase in S.

- The more complex the molecule, the more likely it is to be disorganized and random.

Factors affecting Factors affecting Entropy, SEntropy, S

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- Increasing the amount of a compound will cause the entropy to increase.

- Larger molar quantities have more disorder than smaller molar quantities. Look for the coefficients!

• Entropy increases when a pure liquid or solid is dissolved in a solvent.

• Breaking a solid up into smaller pieces leads to a less organized structure, and more kinetic energy.

Factors affecting Factors affecting Entropy, SEntropy, S

10101010 Practice Problems #1• For each, circle which has a greater entropy (S)

• A) Hg (l) or Hg (s)

• B) C2H4 (g) or C2H6(g)

• C) 1.0 mol of H2 (g) or 2.0 mol of H2(g)

• D) NaCl (s) or NaCl (aq)

• E) NH3(g) or Ne(g)

Predict if entropy is increasing or decreasing:

1) solid sugar is added to water

2) iodine vapor condenses onto a cold surface forming crystals

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Consider the reaction:___H2(g) + ___O2(g) ---> ___H2O(l)

• Would we expect entropy to increase or decrease? Be sure to balance the reaction

∆So = 2(H2O) - [2 (H2) + (O2)]

*Get ∆S values from your chart!*

∆So = 2(69.91) - [2(130.6) + (205.0)]

∆So = - 326.38 J/mol

Calculating ∆S for a Reaction

∆∆SSoo = S = Soo (products) - (products) - SSoo (reactants) (reactants)∆∆SSoo = S = Soo (products) - (products) - SSoo (reactants) (reactants)

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• ∆So = - 326.38 J/mol.K – Negative ∆S means the entropy is decreasing, and the particles are becoming more organized.

• 2 H2(g) + 1 O2(g) ---> 2 H2O(l)

• Entropy decreases, it becomes more organized because 3 moles of gases produced 2 mol of liquid.

• Lots of Motion (Disorder) More organized.

Calculating ∆S for a Calculating ∆S for a ReactionReaction

∆∆SSoo = S = Soo (products) - (products) - SSoo (reactants) (reactants)∆∆SSoo = S = Soo (products) - (products) - SSoo (reactants) (reactants)

13131313Practice Problem #2

• Calculate S at standard conditions

__NiS(s) + __O2(g) --> __SO2(g) + __NiO(s)

*Predict if you think S will be positive or negative

Substance So(J/mol.K)

SO2 248

NiO 38

O2 205NiS 53

14141414Practice Problem #3• Calculate S for__Al2O3(s)+__H2(g) __Al(s) + __ H2O(g)

*Predict if you think S will be positive or negative

Substance So(J/K.mol)

Al2O3(s) ??

H2(g) ???

Al(s) ??

H2O(g) ???

15151515

1 Al2O3(s)+ 3 H2(g) 2 Al(s) + 3 H2O(g)

• Why is enthalpy large and positive?–H2O is nonlinear and triatomic

»H2O is larger and is more complex

–H2 is linear and diatomic

»H2 is smaller and less complex

• The more complex the molecule, the higher the S