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Unit 13 Kinetics & Equilibrium Page 1 of 14
Chemistry – Kinetics, Entropy, Equilibrium, LeChatelier’s Principle, K,
Unit 13 Quiz: Unit 13 Test: Final Project:
VOCABULARY:
1 Chemical equilibrium 2 equilibrium constant 3 Reversible reaction 4 catalyst
5 Le Chatelier’s principle 6 entropy 7 activated complex 8 Chemical kinetic
9 Activation energy 10 collision theory 11 enthalpy 12. Heat of reaction
OBJECTIVES:
Understand how to measure temperature and heat (including units)
Be able to list what affects reaction rate.
Be able to explain the collision theory
Describe enthalpy and entropy.
Be able to label a reaction mechanism, determining if the reaction is endothermic or exothermic
Understand how a catalyst affects reaction rates and a reaction mechanism.
Be able to describe a reversible reaction.
Be able to apply Le Chatlier’s principle to a system in equilibrium.
Be able to write the equilibrium expression and the equilibrium constant, K.
Be able to complete simple calculations for the value of K
Understand what information the value of K conveys
Heat of reaction
Read pgs 514 – 521 and answer the following questions:
1. What is heat of reaction?
2. How is a thermochemical equation different from a regular equation?
3. What is enthalpy?
4. What is the symbol for enthalpy?
5. What is the sign on ∆H for an exothermic reaction?
6. What is the sign on ∆H for an endothermic reaction?
Section 17-2 Driving force of reactions
Read pgs 526-530 and answer the following questions:
1. Do reactions tend to go toward lower energy or higher energy states?
2. What is entropy? Its symbol?
3. Do processes in nature go toward more order or more disorder (lower entropy or higher entropy)?
4. Which has the most entropy solids, liquids or gases?
5. On pg 530 do # 8
Unit 13 Kinetics & Equilibrium Page 2 of 14
On Entropy sheet below OMIT # 8
Unit 13 Kinetics & Equilibrium Page 3 of 14
CHAPTER 17 - The Reaction Process Read info below and then answer the questions that follow.
Different reactions occur at different rates.
A reaction that goes to __completion proceeds until all of one of the reactants is used up and the
reaction stops. A reaction that can occur in both directions is called a __reversible reaction__ and
will eventually reach equilibrium.
A __reaction mechanism___is the step by step sequence of reactions by which the overall
chemical change occurs.
The slowest step, which will determine the rate is called the __rate determining step___
The set of assumptions regarding collisions and reactions is known as the collision theory. The
change in concentration of reactants per unit time is called the reaction rate.
The area of chemistry that deals with reaction rates is known as ___kinetics__
We can use knowledge of reaction rates to determine whether we will have more reactants or more
products at equilibrium.
Reaction rate depends on five things:
1. Nature of reactants (ex. State- s,l,or g; size of particles; bond type/strength)
2.surface area 4. concentration
3.temperature 5. catalyst
The nature of the reactants and concentration will determine the kind of reaction that occurs. For a
reaction to occur between substances their particles must collide and these collisions must result in
interactions (this is known as the collision theory). Reaction rate is proportional to the number of
effective collisions. When an effective collision occurs, the particles may form an activated complex.
The energy required to form this is called activation energy. The nature of the reactants refers to
their complexity and the number of bonds that must be broken and reformed in the course of a
reaction. The larger the surface area, the faster the reaction rate because a larger surface area will lead
to more particles colliding effectively.
Temperature also effects rate. Higher temperature usually produce faster rxns. At higher
temperatures, particles have more kinetic energy and are more likely to collide effectively. The last
thing that affects rate is a catalyst, which increases reaction rate without being permanently changed.
A catalyst lowers the activation energy for a reaction (by providing an alternate pathway for the
reaction). An inhibitor slows reaction rate by preventing it from reacting.
Rate laws relate reaction rate to concentration of reactants; this will be covered in AP Chemistry!
Unit 13 Kinetics & Equilibrium Page 4 of 14
Questions:
1. List and explain (use the idea of collisions in your explanation) the 5 factors that affect reaction rate (you
should know these for the test!)
A.
B.
C.
D.
E.
2. Given: A. hot tea or ice tea and B. sugar cubes or powdered sugar – what combination would dissolve
together the fastest – why? Use the collision theory in your answer.
3. When have you learned about catalysts before? (think Bio) Give an example of a catalyst
4. If we are reacting zinc metal with hydrochloric acid – which would react the quickest – 1.0 M HCl or 2.0 M
HCl – why? (use the collision theory in your answer)
Energy diagram important parts!
__________________________________________________________________________________________________________
At the top of the curve is the ___________________________________________________ – this is also where the
activated complex is located (where the reactants are being changed to the products.
A ______________________________ will lower the activation energy making the reaction occur more quickly.
__________________________________________________________________________________________________________
To find the H (heat of reaction) the difference in the enthalpy of the products – reactants is found. If
the products have more enthalpy – the H is + and the reaction is endothermic (heat was gained). If
the reactants have more enthalpy – the H is – (negative) and the reaction is exothermic (heat was
released).
Unit 13 Kinetics & Equilibrium Page 5 of 14
1. Is the forward reaction exo or endothermic?_______
2. What is the PE for the reactants (of the forward rxn)?___
3. What is the PE for the products (of the forward rxn)?____
4. What is the activation energy of the forward rxn?____
5. What is the activation energy for the reverse rxn? ____
6. What is the heat of reaction (ΔH) for the forward rxn?___
7. What is the PE of the activated complex? _____
8. Draw a dotted line to indicate the addition of a catalyst.
Unit 13 Kinetics & Equilibrium Page 6 of 14
Unit 13 Kinetics & Equilibrium Page 7 of 14
Chemical Equilibrium Read pages 372-373 and pgs 553-555
Reversible reaction : _______________________________________________
Chemical equilibrium: ___________________________________________
_______________________________________________________________________
Dynamic state: reactions are continually happening .
Ex: physical equilibrium: rate of water evaporating and condensing
is equal – so the overall amount of water (in a closed system) does not change.
Equilibrium constant: K or Keq or Kc
K = [products]coefficients brackets in chemistry represent concentration
[reactants]coefficients
Why use K?
K = 1 ______________________________________________________________________________
K< 1 ______________________________________________________________________________
K> 1 ______________________________________________________________________________
Very Important:
K includes only gases and aqueous solutions; liquids and solids do not have a concentration
Graphs representing equilibrium:
For the first graph together:
A. Label the reactant(s) and the product(s)
B. Write an equation for the rxn
C. label where equilibrium is reached.
D. are there more reactants or products at equilibrium?
E. What type of value would you expect for K?
********For graph # 2 : answer the same questions as above A - E
Unit 13 Kinetics & Equilibrium Page 8 of 14
Example 1: Write the equilibrium expression for: N2 (g) + O2 (g) 2 NO (g)
Calculate the value for K if [N2] = .32, [O2] = 1.1 and [NO] = 2.1
You try: Given: 2 HF (g) F2 (g) + H2 (g)
A. Write the K expression
B. Calculate the value of K if [HF] = 6.2 [F2] = 3.1 and [H2] = 2.2
C. Do you have more reactants or products?
PRACTICE/You try:
1. Write the expression for the equilibrium constant for each of the following reactions and then calculate the
value of the equilibrium constant for those with values listed .
A. 2 CO(g) + O2 (g) 2 CO2 (g) B. CaCO3(g) CaO(g) + CO2(g)
C. 2 SO2(g) + O2(g) 2 SO3(g) D. H2(g) + Cl2(g) 2 HCl(g)
[SO2] = 0.001 [O2] = 0.002 [SO3] = 0.003 [H2] = [Cl2] = [HCl] = 1.0 x10-2 (all the same)
E.. N2(g) + 3 H2(g) 2 NH3(g)
[N2] = .044 [H2] = 0.12 [NH3] = 0.0034
Acids, Bases, and water
There are different Ks for different substances. Ka is used for acids (substances that begin with H) Kb is
used for bases – (substances that contain OH-). We will study acids and bases next chapter. Ksp is used
for insoluble solids (ppts) and Kw is used for aqueous solutions.
Kw = dissociation constant for water Does not include H2O because it is a pure liquid with no concentration!
Example: H2O(l) H+1(aq) + OH-1(aq)
Kw = [H+] [OH-]
Unit 13 Kinetics & Equilibrium Page 9 of 14
Extra PRACTICE/You try: Write the K for the following equations, calculate the value and predict if
there are more products or reactants at equilibrium
Equation K expression and math work K value More products
or reactants
2H2S(g) 2H2 (g) + S2 (g)
[H2S] = 0.25, [H2] = 0.88, [S2] = 0.44
2H2S(g) 2H2(g) + S2 (g)
[H2S] =0.18, [H2 ] = 0.014
[S2] = 0.035
2N2O5(g) 4NO2(g) + O2 (g)
[N2O5] = 0.50, [NO2] = 0.80, [O2] = 0.20.
Le Chatelier’s Principle A system at equilibrium will shift to adjust to changes to stay at equilibrium.
Conditions:
1. Concentration: A. Increase/add shifts away (to consume excess)
B. Decrease/Remove shifts towards (to replace)
2. Pressure: A. Increase shifts to side with less gaseous moles
B. Decrease shifts to side with more gaseous moles
3. Temperature: – depends on if rxn is exothermic or endothermic
Temperature is the only condition that changes the value of K
4. catalyst – does not produce a shift – rxn speeds up in both directions!
Example: Predict the shift when PCl5 (g) PCl3 (g) + Cl2 (g) exothermic
A. add PCl5
B. Remove PCl5
C. Increase P
D. Decrease T
E. Add Cl2
You try: 2CO (g) + O2 (g) 2 CO2 (g) + 167 kJ
A. Add CO2 C. Decrease pressure
B. Remove O2 D. Decrease temperature
Unit 13 Kinetics & Equilibrium Page 10 of 14
Le Chatlelier’s principle practice!
Given: 12.6 kJ + H2 (g) + I2(g) 2 HI (g)
Stress Shift [H2] [I2] [HI] K
1. Add H2 xxxxxx
2. Add I2 xxxxx
3. Add HI xxxxx
4. Remove H2 xxxxx
5. Remove I2 xxxxx
6. Remove HI xxxxx
7. Increase Temp
8. Decrease Temp
9. Increase Pressure
10. Decrease Pressure
Unit 13 Kinetics & Equilibrium Page 11 of 14
Review Sheet
1. List the 5 factors that affect reaction rate.
2. Processes in nature go toward: higher or lower energy
3. Processes in nature go toward higher or lower disorder (entropy)
4. SKIP!
For the following match the correct symbol and definition:
5. H A. Celsius Temperature
6. T B. Free Energy E. Kelvin Temperature
7. S C. entropy F. enthalpy D. reaction rate
9. Which has more entropy an ice cube or liquid water?
10. Does dissolving salt in water cause an increase or
decrease in entropy?
Use the graph below to answer the following questions:
11. Which letter represents the relative energy of the
activated complex?
12. Which letter represents the energy of the reactants?
products?
13. Which letter represents the difference in energy between
reactants and products?
14. Which letter represents the activation energy for the
reverse uncatalyzed reaction?
15. Is this reaction endothermic or exothermic?
16. Which letter represents the activation energy of the
forward catalyzed rxn?
REVIEW SHEET Equilibrium
PRACTICE: N2 (g) + 3 H2 (g) 2 NH3 (g)
1. Write the Keq for the above reaction and determine its value, if [N2] = .3, [H2] = 1.7 and [NH3] = 0.7
2. Are there more products or reactants at equilibrium?
3. Given: 2 NO3 (g) 2 NO2 (g) + O2 (g) + 30 kJ
How would the system shift if:
A. more Nitrogen dioxide is added
B. Which of the above changes would affect the value of the equilibrium constant?
C. Some of the nitrogen trioxide is removed?
D. The pressure is decreased?
E. How would the concentration of nitrogen dioxide be affected by B?
F. The temperature is increased?
Unit 13 Kinetics & Equilibrium Page 12 of 14
Unit 13 Kinetics & Equilibrium Page 13 of 14
Le Chatelier’s lab Do NOT write on this sheet
In this experiment, you will investigate what happens when the conditions of equilibrium are changed. The
equilibrium you will be investigating can be described by the following equation:
CuCl4-(aq) Cu2+(aq) + 4Cl-(aq) + heat
Green blue colorless
Materials: 1.5 M CuCl2 .05 M AgNO3 salt solution small test tubes well-
plates safety glasses test tube rack
Procedure
Caution: You must wear safety glasses at all times during this experiment.
Part A: How do temperature changes affect the equilibrium?
1. Place 1-3ml of 1.5 M copper(II) chloride, CuCl2, in a clean, labeled test tube. Place another 1- 3 mL of
1.5 M CuCl2 in a second and third test tube.
2. Place one of the tubes in a test tube rack or empty beaker. This will be used as a reference for
comparison.
3. Heat the second tube of copper (II) chloride solution in a boiling water bath for several minutes.
Carefully record any observations you make. (Be sure to compare it to the reference solution.)
4. Cool the second tube of copper (II) chloride solution in an ice water bath for several minutes. Carefully
record any observations you make. (Be sure to compare it to the reference solution.)
5. Look at the equation for the equilibrium. Try to identify the substances that have increased in
concentration and the substances that have decreased in concentration
6. Remove the tubes and place them in your test tube rack or in an empty beaker. Unplug the hot plate
but leave hot and cold water for the next class!
Part B:
How do concentration changes affect the equilibrium?
1. Make sure your well plate is clean. In each of two wells, place 3 drops of room temperature copper (II)
chloride solution. One well will be used as a reference to compare with the other. Put a piece of white paper
under the well plate to make it easier to see.
Caution: When using pipettes, leave the pipette for each solution in the test tube with the solution
so they do not get mixed-up.
2. Add 2 drops of sodium chloride solution, a drop at a time, to one of the wells. (This increases the
concentration of chloride ions, Cl-.) Carefully record your observations.
3. Now add one drop of silver nitrate solution to same well that you added the sodium chloride solution
to. (This decreases the concentration of chloride ions because the white solid that forms is silver
chloride, AgCl .) Carefully record your observations.
4. Look at the equation for the equilibrium. Try to identify the substances that have increased in
concentration and the substances that have decreased in concentration.
5. Clean up by rinsing off the well plate – dump the CuCl2 that was cooled or heated back into the original
beaker (do not dump the well plate chemicals into the original beaker).
6. Unplug hot plate but leave hot water on the plate. Leave ice water for next class!
Unit 13 Kinetics & Equilibrium Page 14 of 14
Le Chatelier’s lab Answer sheet Name:___________________________
Data table: Copy the equation (including colors) :
Change observations Shift (left or right?)
1. heating solution
2. cooling solution
3. adding NaCl
4. adding AgNO3 (removing Cl-1 )
Questions:
1. Which way did the system shift when it was heated? _______________
2. how do you know?___________________________
3. Which way did the system shift when it was cooled?______________________
4. How do you know?____________________________
5. What happened to the concentration of the Cl- when heat was added? _____________
6. What happened to the concentration of the Cl- when heat was removed? _____________
7. Which way did the system shift when NaCl was added?_____________
8. Why did this shift occur?____________________________________
9. Which way did the system shift when AgNO3 was added?______________
10. Why did this shift occur?________________________
11. Predict the shift that would occur if Cu2+ was added __________________
Why?______________________________________________
12. Predict the shift that would occur if the pressure was decreased____________
13. Why would this occur?__________________
Test review
14. A. Write the K expression for the equation: 2SO 3 (g)⇌2SO 2 (g)+O 2 (g)
B Calculate the value of K if [SO3] = 4.2 [SO2] = 1.2 and [O2] = 1.4 Show work!