+ Catalyst What does “reversible” mean? Give examples of a reversible physical or chemical process.  Objectives  I can define chemical equilibrium and identify systems that are in chemical equilibrium.  I can investigate factors that shift chemical equilibrium..  Agenda  Catalyst  Exit Slip and HW review  Demonstration & simulation: Equilibrium  Exit Slip  Take out your HW!

+ Exit Slip Review (1) Chemical reaction rate may be measured by the (disappearance/production) of reactants or the (disappearance/production) or products. (2) C 3 H 8 (g) + 5 O 2 (g)  3 CO H 2 O(g) All of the following are acceptable methods of measuring the rate of the above reaction EXCEPT a) the rate of consumption of C 3 H 8 b) the rate of production of O 2 c) the rate of production of CO 2 d) the rate of production of H 2 O

+ Exit Slip Review (3) The following reaction rate expression contains 3 mistakes. Circle and correct the mistakes. 2 Na + 2 H 2 O → 2 NaOH + H 2 rate = - Δ [Na] = - Δ [H 2 O] = Δ [NaOH] = Δ [H 2 ] 2 Δ t 2 Δ t 2 Δ t 2 Δ t (4) As the reaction in #3 proceeds, what will happen to the amount of reactants? The amount of reactants will decrease.

+ (5) Hydrogen gas (H 2 ) is produced in the reaction of magnesium (Mg) and hydrochloric acid (HCl): Mg(s) + 2HCl(aq)  H 2 (g) + MgCl 2 (aq) Which will slow the rate at which H 2 is produced? a) using one chunk of Mg instead of powder b) increasing the concentration of HCl c) heating the HCl to 30 o C d) decreasing the pressure on H 2 (6) List at least three factors that affect reaction rate: temperature, reactant concentration, pressure (gas), surface area

+ (7) A student observes the reaction of zinc metal (Zn) and hydrochloric acid (HCl) under various conditions. When 6.0 M HCl is used instead of 1.0 M HCl, there is increased bubbling. This can be explained by an increase in ___________ at a higher molarity. a) energy of the HCl molecules b) collisions between HCl and zinc c) surface area of the zinc atoms d) activation energy of HCl (8) How does increasing temperature affect the reaction rate? Why? Increasing temperature increases the reaction rate because there are more collisions with enough energy to start a reaction.

+ Exit Slip 8c Review (1) Catalysts speed up chemical reactions by (a) providing more energy for the reactants. (b) being used up to create more products. (c) lowering the activation energy. (d) lowering the difference in potential energy between reactants and products. (2) Hydrogen peroxide naturally breaks down into water and oxygen gas over time. Manganese dioxide can be used to lower the energy of activation needed for this reaction to take place, and, thus, increase the rate of reaction. What type of substance is manganese dioxide? (a) a catalyst (c) an enhancer (b) an inhibiter (d) a reactant

+ (3) Which arrow represents the part of the reaction most likely to be affected by the addition of a catalyst? (a) A(c) C (b) B(d) D (4) See diagram. Activation Energy

+ 8a, 8b, and 8c Make Up Assignments For 8a and 8b: Turn in your completed and well-written HW assignment -- pp. 597 #1, 7, 12, 14, 18, pp. 598 #26, 29 For 8c: pp # 5, 8-11 – answer and justify answers.

+ Start Up: Think Box Take 1 minute to write as many things as you can think of in the box at the top of your Notes Day 3 worksheet. When you think of the word EQUILIBRIUM, what do you think of?

+ Definition of equilibrium Using the scenarios we just wrote down, what is a possible definition of equilibrium. Put it in your own words, write down how YOU would define equilibrium… Your definition does not have to sound scientific Equilibrium is the exact balancing of two processes, one of which is opposite of the other. Equilibrium implies “balance” or “steadiness”

+ What is chemical equilibrium? Chemical equilibrium is a state of balance in which the rate of a forward reaction equals the rate of the reverse reaction and the concentrations of the products and reactants remain unchanged.

+ Completion Reaction vs. Reversible Reaction Completion ReactionReversible Reaction When a chemical equation only has one arrow (  ) we say that reaction goes “to completion” Example: NaCl  Na + + Cl - All of the NaCl breaks up into ions Some chemical equations have two arrows in them:   Ex: H 2 SO 4  2H + + SO 4 2- Forward reaction: Reverse Reaction: If an equation has a double arrow it has reached equilibrium!

+ White Board Practice Instructions: Write your answer on your white board. When Ms. Boon says go, hold up your white board.

+ White Board Practice PCl 5  PCl 3 + Cl 2 Is this a completion reaction or a reversible reaction? How do you know?

+ White Board Practice PCl 5  PCl 3 + Cl 2 Write the forward reaction: Write the reverse reaction:

+ White Board Practice 2 H 2 (g) + O 2 (g) → 2 H 2 O (l) Is this a completion reaction or a reversible reaction? How do you know? Label the reactants and the products.

+ Demonstrations! Listen and watch carefully during the demonstrations. Answer the questions on your worksheet as we go.

+ But what does that mean? Imagine two escalators moving people up and down in between floors of a department store and there are 100 people on each floor. Do the math: How is the number of people changing if 5 people per minute are always going UP to the next floor and 10 people per minute are always going DOWN to the floor below? What are the numbers after 3 minutes?

+ Summing it Up! At Equilibrium… HCl + NaOH  H 2 O + NaCl At equilibrium the concentrations of products and reactants are not changing The forward reaction is happening at the same time as the reverse reaction We say that the forward rate is the same as the reverse rate This means the amounts of products and reactants stays the same

+ Exit Slip Expectations: You will work silently and independently. When you are done, cover your exit slip with your handouts. Tools: You may use all your notes, worksheets, and flash cards. You may use your own calculator. What do I turn in? You will turn in your exit slip only. Homework: pp problems pp. 501 #1-3, 6, 7 Intro to LeChatelier: read pp answer questions: (1) Define Le Chatelier’s principle. (2) Explain how changing reactant or product concentration changes equilibrium. (3) Explain how increasing temperature affects equilibrium of an endothermic reaction and exothermic reaction. (4) When does changing pressure affect equilibrium?

+ Exit Slip Part 1: Write at least 5 sentences explaining what chemical equilibrium is. Use examples from class. Use the key terms: reversible reaction, completion reaction, and chemical equilibrium. Part 2: Grade your level of understanding of the current unit on a scale of 1 – 4. 4 is the highest.