HW 11-12 Entropy (S)- A measure of Randomness or Disorder Concept of Entropy helps us understand the natural direction of processes

Entropy and the Second Law of Thermodynamics – “The Universe Tends Towards Maximum Disorder” For any spontaneous process, the entropy of the universe increases

Spontaneous Processes Process that occurs without outside intervention “i.e. something happens on its own” Processes that are spontaneous in one direction are nonspontaneous in the reverse direction. Energy has to be added to make a nonspontaneous process go. Spontaneous ≠ Fast

ENTROPY AS TIME’S ARROW Concept of Spontaneous vs Nonspontaneous: Which clip represents what actually happens in our universe? ENTROPY AS TIME’S ARROW Link to breaking glass forward and reverse Link to diffusion of food coloring I Link to diffusion of fooding coloring 2 Link to nuclear explosion 1 Link to nuclear explosion reverse

Concept of Spontaneous 1) Dinner plate and shatters into many irregular pieces. 2) Over a couple of weeks, your room cleans itself; clothes fold themselves and migrate to drawers. 3) A rock rolls itself up a cliff and balances on a ledge. 4) The random motion of N2 and O2 molecules of an entire classroom of air end up in one corner of the room leaving the students in a vacuum. YES! NO! NO! NO!

Entropy, S Concept of Entropy is related to number possible arrangements of atoms or molecules A spontaneous change increases entropy by increasing the number of possible positions particles can occupy

↑Microstates, ↑ Entropy Atom = 1 microstate

↑Microstates, ↑ Entropy Atom = 1 microstate 3 microstates(entropy increasing)

↑Microstates, ↑ Entropy Atom = 1 microstate 3 microstates(entropy increasing)

↑Microstates, ↑ Entropy Atom = 1 microstate 3 microstates(entropy increasing)

↑Microstates, ↑ Entropy Atom = 1 microstate 3 microstates(entropy increasing) 5 microstates (entropy increasing)

Concept of microstates or arrangements, which has more possible ways to arrange things? 1) Socks folded together with their matched partner placed in top drawer of your dresser vs individual socks hanging from the lamp and desk chair, under your bed, in your bed.

Concept of microstates or arrangements, which has more possible ways to arrange things? 1) Socks folded together with their matched partner placed in top drawer of your dresser vs individual socks hanging from the lamp and desk chair, under your bed, in your bed.

Increasing Temperature (kinetic energy of molecules) increases Entropy Link to Gases Phet If temperature is increased (at constant pressure) gases will expand. Greater volume occupied → Greater # of possible positions = greater Entropy

Which has higher entropy (more possible positions for ions), solid NaCl or NaCl dissolved in water? ANS: NaCl dissolved in water has greater entropy. Separated ions can occupy many more positions. NaCl(s) → NaCl(aq) ; ∆S = +

Concept of microstates or arrangements, which has more possible ways to arrange things? 1) Atoms in the solid phase vs atoms in the liquid phase vs atoms in the gas phase

Entropy and Phases of Matter Entropy Gas >> Entropy Liquid > Entropy of Solid

Entropy, S ∆S = change in entropy ∆S = +, entropy increasing (more arrangements of particles possible) ∆S = -, entropy is decreasing, (fewer arrangements of particles possible)

Predicting Entropy Changes 1) H2O (l) → H2O (s) H2O (s) → H2O (l) ∆S = - ∆S = + Reverse direction process, reverse sign – true for both H and S

Predicting Entropy Changes 2) CO2 (s) → CO2 (g) ∆S = +

Ba(OH)2∙ 8 H2O(s) + 2 NH4SCN(s) → Ba(SCN)2(aq) + NH3(g) + 10 H2O (l) ∆S = +