Rate & equilibrium

Outline:•Rate•Reactions & collision theory•Graphs w/ activation energy of endo & exo•4 factors that affect rates of reaction•Read chapter 17•Students should take notes & copy diagrams (might have space after vocab)

Sample notes

• What is rate?• What factors affect rate?• What is collision theory? • Samples of exothermic and endothermic graphs of reaction rate

Lab/demosZinc in HCl, 2

concentrations, Zn, different surface areas,

matchesWHEN is it done?

Catalyst demo (shows activity complex*)

Heat 300 ml ofA to 80C then add 100 mlH202 observe then add 30 ml of catalyst CoCl2

Surface area bottle

What is rate?

• Describe these rates:– When we light a match– We put zinc in HCl (2 different concentrations)

• How do we know when the reaction is done?

Rate of reaction

•can be determined by measuring the rate at which reactants are used up or the rate at which products are formed.

• A would be increasing rate: likeexplosive (gun powder)• B is a constant rate (like how soaps work)• C is slowing down, like what refrigerators would do• KEY: Chemists work on controlling rates.

Discuss rates at various points.

Collision theory• Reactants have to strike each other with sufficient energy and in the correct configuration in order for the reaction to occur.

• Kicker will share an example of students at a dance.

• Reactants must hit with:– 1. sufficient energy– 2 correct config. Or orientation

• In order for a reaction to progress.

Consider a simple reaction involving a collision between two molecules -

ethene, CH2=CH2, and hydrogen chloride, HCl.

These react to give chloroethane.As a result of the collision between the two molecules, the double bond between the two carbons is converted into a single bond. A hydrogen atom gets attached to one of the carbons and a chlorine atom to the other.

During a reaction

• An intermediate particle is formed. It is neither reactants nor products. This happens when there is enough energy & proper orientation of the reactants. This is called an activated complex. This is an intermediate that does not stick around long.

See catalyst demo & color change!

Discuss activation

energySee page 597 graph.

What causes paper to burn?

Kicker will burn some paper and discuss the graph it would make.

Wave it in the air, rub it like two sticks, then use a heat source

Activation energy

The activation barrier must be crossed before reactants are converted to products. The activated complex is a temporary arrangement of particles that has sufficient energy to become either reactant or products.

∆T∆T

Class Question

This is an exothermic reaction. The products have less energy than the reactants. But it took a lot of activation energy to get it going. Most of these reactions are self sustaining as they have enough energy to keep going.

This is an endothermic reaction. The products have more energy than the reactants. These reactions are not self-sustaining because not enough energy is released to keep the reaction going. Endothermic reactions need a constant supply of energy to keep going.

Some examples are ice melting, evaporation, photosynthesis

Photosynthesis

• CO2 + H20 + light --> C6H12O6 + O2

SAMPLE QUIZ ?s

What do you have at A, B, & C. What is D? Is this exo or endo?

I get this, but how can we control the rate of the reaction?

4 methods of increasing the rate of

reaction.• Temperature• Catalyst• Surface area• Concentration.

Temperature

• If temp. increases, kinetic energy increases and so do the number of collisions.– If temperature decreases, the opposite is true

• A 10 C increase in temp will approximately double the rate of reaction

• A 30 C increase will cause an increase in rate of 8 times faster. (note that it is exponential)

Catalyst• This is a substance which changes the rate, without undergoing any permanent chemical change itself. It does this by lowering the activation energy by allowing a a different path for the reaction to occur.

Write this reaction

• The rate of the decomposition of hydrogen peroxide (dihydrogen dioxide) into water and oxygen gas can be increased by adding the catalyst manganese dioxide. (Put the catalyst above the arrow)

Video of how this catalyst works.

Kicker will draw another example

Which of these could use the help of a

catalyst?

Summary

Some reactions are simply faster because of the nature of the

substances.• Ions in solution can react faster

• AgNO3 + Cl- --> AgCl (s)

• Covalent with covalent are usually slow because you have to break tough bonds before other bonds can form.

• N2 + H2 -->NH3

• Br2(l) + C6H11 (aq) --> C6H11Br + HBr

Assignment

Do pg 3 NOWAssign pg 4 & 5 in packet Read pg 595-600 & 626Read Iodine Clock Lab in packet pg 6 (get ONLY 80 ml each A & B)WE will DEMO temp.

Assignment

• You need to read equilibrium pages in our book

• Pg 601-604 & 612-619*ignore math for now, we’ll do that later

• DO pg 628 # 4, 5, 6, 8, 9 & study for a quiz

Reversible Reactions & equilibrium

Lecture reversible reactions, equilibrium & shifts.BE SURE YOU HAVE READ PG 601-604

Use the worksheet as notes

Equilibrium Ch 17Review rate… How is it measured?

2Zn + 2HCl --> H2 + 2ZnCl

Collision theoryFactors affecting rate

1.gas given off -

Mg + 2HCl McCl2 + H2(g)

2.insoluble product is formed -

AgNO3(aq) + KCl(aq) KNO3(aq) + AgCl (s)

3.molecular product formed -

HCl(aq) + NaOH(aq) NaCl(aq) + HOH (L)

DO YOU REMEMBER double displacement when there was no reaction.

Most reactions are irreversible, that is, they go to completion.

Equilibrium is the

• State at which the concentration of all reactants and products remain constant.– See pg 602

These equilibrium rxns. Are reversible

A + B C + D

A + B C + D is forward rxn

C + D A + B is reverse rxn

If A + B is forming C + D as fast as C + D is forming A + B, the reaction is at equilibrium. The rate forward and backward is equal.

• NOTHING SAYS THAT THE CONCENTRATIONS ARE EQUAL THOUGH!

Demo… shake clear--->blue

– WHAT AM I DOING TO MAKE IT GO?– As we agitate it it becomes oxygenated. This shows reversibility

At equilibrium,

• it appears as if nothing is happening, but reactants are still forming products and products are forming reactants at the same rate.

• NOTE: The concentration of P & R are not necessarily equal. Long arrow points to where you have more.

See diagram 603

See worksheet graphs– Graphically. See pg.– Look carefully at the axis.– Why do some come down? (green & purple)?

Test Tube & Straw Device

• When are we at equilibrium?

• PG 602: EQUILIBRIUM: a dynamic state where the concentrations of the R and P remain constant over time, as long as conditions are not changed. (such as pressure, temp, # particles)

Which do we have more of?

• H20 + HC2H3O2 H3O + + C2H3O2 -1

• H20 + HClO4 H3O + + ClO4 -1

• Discuss INDUSTRY. This is only 78.2% complete, What if I want to make more

• H2 + I2 2HI

Homo Vs Hetero

• Homogenous all the same state of matter

• Heterogeneous P & R are in different states of matter.

• Just and FYI in case you hear about these in your reading.

Le Chateleir’s principle.

IF STRESS IS APPLIED TO A SYSTEM IN DYNAMIC EQUILIBRIUM, THE SYSTEM CHANGES TO RELIEVE THE STRESS.

“Things move in the direction that relieves the stress”

or

“the system rolls with the punches”

Shifts (see worksheet)

• Concentration (soln. &gases only)

• More, concentrated will shift to make more.

• See Pg 612-613• Removing a product always pulls the reaction toward the product.

• “Removing something, pulls it that way!”

Temperature (soln & gases)

A + B + heat C endothermic in the forward direction

A + B C + heat exothermic in the forward direction

Adding heat favors the endothermic reaction. WHY?

DEMO

•2NO2 (g) N2O4 (g) + heat

•N2O4 is clear

•The reverse reaction is endothermic.

• LET’S TRY COOLING IT, HEATING IT

Pressure and volume (for gases only)

2A(g) + B(g) 2C(g)

• A change in pressure affects only a system that has an unequal number of moles of gaseous reactants and products.

• If you have more pressure the system will adjust to take up less space. (pg 617)

Increase pressure

In the Haber process (pg 612)

N2(g) + 3H2 (g) 2NH3 (g) + heat

1. Adding heat will do what?2. Adding pressure?3. Removing pressure?4. Removing product?5. Adding reactant?

Try worksheet examples

Try these

• Pg 615 ex 17.4 then exercise #17.4

• Pg 617 ex 17.5 pg 618 exercise 17.5

• Pg 619 ex 17.6 exercise 17.6

LAB

• This is on page 13 & 14 of your packet

Keq lecture pg 605-610, 620-

• Keq is a value the tells us which direction a eversible reaction is favored. Toward products or toward reactants.

• USE HANDOUT first in packet, then see ppt.)– Book probs.pg 628… 18-21, 38-42, 65, 68, 59

– Know what Keq values mean!– Be able to write expressions & do calculations for Keq. (look ahead at Ksp)

Solids(s) & liquids(l) are NOT included.

• PRACTICE: 1. Calculate the Keq for this reaction given the concentrations at a constant temperature are as follows:

[NO2] = 8.8 M[NO] = 1.2 M [O2] = 1.6 M

2NO(g)+O2 (g) ⇌2NO2 (g)

• PRACTICE: 2. write the equilibrium equation for this reaction:

2Na(s)+CuCl2 (aq) ⇌ Cu (s)+ 2NaCl

(aq)

• PRACTICE: 3. Calculate Keq for the above reaction (practice 2) if the concentrations are as follows: [CuCl2] = 0.050M & [NaCl] = 0.50M

2Na(s)+CuCl2 (aq) ⇌ Cu (s)+ 2NaCl (aq)

SO WHAT DO Keq VALUES MEAN?• Recall that the equations for Keq is a fraction.

So, if the value of Keq > 1 (greater than 1), then that means the numerator is larger than the denominator. So which direction would be favored in the reaction? ___________ (product or reactant?)

• Keq >1 favors products of forward reaction

• Keq<1 favors reverse reaction (reactants)

YOU TRY THIS ONE

WORK THRU PRACTICES IN PACKET

How does as shift affect Keq

• Shifts in pressure or quantities do NOT change Keq

• Shifts as a result of temp change do affect Keq

Book probs.• Pg 606 17.1• Pg 610 17.3• Pg 611 1, 2 & 5• Pg 619 17.6

You may see this. . . Ksp

(pg 622) • This the the constant of solubility we write these the same way.

AssignmentWorksheets & BOOK QUESTIONS on your own paper to turn in tomorrow!

Practices in packetPg 629..: 18-21, 29, 31, 32, 33, 34, 38-42, 65, 68, (59 challenge)

Work on problems

• Remainder of Quick reviews by tomorrow

• Rate /equilibrium quiz • Still: Nuclear information