List at least four observations that would indicate a chemical reaction is taking place.

Color Change Energy change (heat/light) )

Production of a solid Production of a gas

Do reactions only procede forward (R → P) or can they go also go in reverse (P → R)? Reversible reaction Link to phet reversible REACTIONS CAN GO IN BOTH THE FORWARD AND REVERSE DIRECTIONS! Link to Chemical Oscillator

Link to Rings of Color NO! ALL CHEMICAL REACTIONS IN A CLOSED SYSTEM WILL EVENTUALLY REACH CHEMICAL EQUILIBRIUM Link to Briggs-Rausher

NO Color CHANGES NO Temperature CHANGE NO solid or gases products appearing

Reaction Simulation Activity: Partner Activity, 1 cup of beans between two partners R P Overall Rxn Rate = Difference between forward rate (R → P) and reverse rate (back rate, P → R). Equation for rate: Rate = k[N], where k = rate constant and N is # of reacting particles. We will simulate a reaction with a forward rate constant k = ½ and a back rate, k = ¼. Forward Rate: Rate = ½[N] Reverse Rate: Rate = ¼[N]

Table #1: Round #1 Reactant Person: Rate = ½[40] = Product Person: Rate = ¼[0] = Reactant person transfer 20 to product person; product person transfer zero back; Each partner count total and record results in outcome. 20 0

TABLE 1 R R P P # OF BEANS # TRANSFERRED # OF BEANS # TRANSFERRED INITIAL ST TRANSFER OUTCOME

Table #1: Round #2 Reactant Person: Rate = ½[20] = Product Person: Rate = ¼[20] = Reactant person transfer 10 to product person; product person transfer 5 back; Each partner count total and record results in outcome. Work through rounds 3 & 4 on your own. Round fractions. Example #1: 15 ÷ 2 = 7.5 → 8 Example #2: 25 ÷ 4 = 6.25 →

TABLE 1 R R P P # OF BEANS # TRANSFERRED # OF BEANS # TRANSFERRED INITIAL ST TRANSFER OUTCOME ND TRANSFER OUTCOME RD TRANSFER OUTCOME TH TRANSFER OUTCOME

TABLE 2 R R P P # OF BEANS # TRANSFERRED # OF BEANS # TRANSFERRED INITIAL ST TRANSFER OUTCOME ND TRANSFER OUTCOME RD TRANSFER OUTCOME TH TRANSFER OUTCOME

Questions (After 4 th transfer) 1) Compare # beans transferred R → P to R ← P. 2) Compare forward and back rates: 3) Is outcome changing? 4) Ratio of P/R in table 1 and table 2 5) Term for forward rate = back rate and [R] and[P] are constant: # is EQUAL; Table #1 7:7 ; Table #2: 10:10 NO; Table #1 13:27 ; Table #2: 20:40 RATIO P/R FOR BOTH ≈ 2. Table #1 27/13 ; Table #2: 40/20 EQUILIBRIUM

Table #1 Graph: #Beans vs. outcomes # BEANS INITIAL 1 ST OUT 2 ND OUT 3RD OUT4TH OUT EQUILIBRIUM

Table #1 Graph: #Transferred vs. transfer step # TRANS 1 ST Trans 2 ND Trans 3 RD Trans4 th Transfer EQUILIBRIUM

Chemical Equilibrium

NET Concentrations of Reactants and Products are constant (not changing) Forward Rate = Reverse Rate No visible changes taking place

Dynamic Equilibrium – at equilibrium the forward and backward reactions are still taking place but at equal rates Link to phet reversible

NO 2 ↔ N 2 O 4 Link to NO2 equilibrium McGraw Hill

At what point (A,B, or C) has chemical equilibrium been reached? C B A

C B A

At point A, which is faster the forward or reverse reactions? At which point has chemical equilibrium been reached? A B C

A B C

HW 11-3, p. 543, #3-12 (WB, p. 100) 3) How do chemists envision reactions taking place in terms of a collision model For reactions? Give an example of a simple reaction and how you might envision the reaction taking place by means of collisions between molecules.

Summary OF Collision Theory RXN RATE = RXN RATE = # of collisions x fraction with correct energy x fraction with correct orientation

HW 11-3, p. 543, #3-12 (WB, p. 100) 4) What does the symbol Ea stand for and what does it represent in terms of a chemical reaction? Ans: Ea = Activation Energy; the minimum amount of energy needed to initiate a chemical reaction.

HW 11-3, p. 543, #3-12 (WB, p. 100) 5) A catalyst works by providing an alternative pathway by which the reaction may take place with reaction having a lower than the pathway followed when the catalyst is not present. 6) What are enzymes and why are they important? Ans: Enzymes are proteins which catalyze chemical reactions in cells. Without enzymes, the chemical reactions needed to sustain life would be too slow. Activation Energy

HW 11-3, p. 543, #3-12 (WB, p. 100) 7) How does equilibrium represent a balancing of opposing processes? Give an example of an “equilibrium” encountered in everyday life, showing how the opposing processes oppose each other. Possible Answer: If population of a town is 100,000 at the beginning and end of a year, best explanation is an equal # of people moved in and out of town, not that no one moved in or out during an entire year.

HW 11-3, p. 543, #3-12 (WB, p. 100) 8) How do chemists define a state of chemical equilibrium? 9) What does the use of a double arrow, indicate about a chemical reaction? Ans: Reaction is reversible. Reactants and products are interconverted back and forth. NET Concentrations of Reactants and Products are constant (not changing) Forward Rate = Reverse Rate No visible changes taking place

HW 11-3, p. 543, #3-12 (WB, p. 100) 11) What does it mean to say that a chemical or physical equilibrium is dynamic? Answer: The forward and reverse reactions are still taking place, but at equal rates.

12) For the reaction H 2 O + CO ↔ H 2 + CO 2. What is the significance of the portion of the plot where the two main curves join together to form a single curve as time increases? H 2 O + CO → H 2 + CO 2 H 2 + CO 2 → H 2 O + CO