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Name: _______________________ Date: ______________

Unit 8: Chemical Kinetics Regents Chemistry

Aim: ______________________________________________________________

Do Now: a) Using your glossary, define chemical kinetics:

_______________________________________________________________________

_______________________________________________________________________

b) Sort the phrases on the SmartBoard into the two columns below.

Remember: Every chemical reaction, whether endothermic or exothermic, requires BOTH an INPUT and an OUTPUT of energy!

Gummy Bear Demonstration:

__________________________________________

Endothermic Rxns Exothermic Rxns

Sketch of Representative

Endothermic Potential Energy Diagram

Sketch of Representative

Exothermic Potential Energy Diagram

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Practice: Write out the chemical equation for each of the following rxns.

Determine whether each is endothermic or exothermic. Draw a sketch of the

correct potential energy diagram.

1. Methane gas, CH4, undergoes a combustion reaction to form the products of complete

combustion, carbon dioxide and water vapor. (Recall another reactant necessary for

combustion!) Chemical Equation:

Potential Energy Diagram Sketch

Endothermic or Exothermic?

Type of Chemical Reaction:

2. Water is decomposed into its elements by the process of electrolysis.

Chemical Equation:

Potential Energy Diagram Sketch

Endothermic or Exothermic?

Type of Chemical Reaction:

3. Zinc metal reacts with aqueous hydrogen chloride, HCl (also known as hydrochloric acid). The

products of this reaction are aqueous zinc chloride and hydrogen gas, which bubbles out of the

solution. The flask that the reaction occurs in gets very hot. Chemical Equation:

Potential Energy Diagram Sketch

Endothermic or Exothermic?

Type of Chemical Reaction:

4. Iron metal combines with oxygen to form rust, or iron III oxide. Energy is released. Chemical Equation:

Potential Energy Diagram Sketch

Endothermic or Exothermic?

Type of Chemical Reaction:

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Name: ____________________ Date: _________________ Period: ______

Do Now: Practice Interpreting Graphs & Diagrams Directions: Answer the questions that follow based on the graphs below, which show the energy

changes that occur during chemical reactions.

1. Label each graph as either endothermic or exothermic.

2. Compare the energy of the reactants (PER or HR) to the energy of the products

(PEP or HP) for each g raph.

3. In the exothermic graph, the reactants are hydrogen and oxygen molecules, and the

product is water. Write the thermochemical equation for this reaction.

In the endothermic graph, the reactant is water and the products are hydrogen and

oxygen molecules. Write the thermochemical equation for this reaction.

1.

2.

3.

4. Both graphs have a peak in the middle of the graph. Highlight this peak. The double-

headed arrow beneath the peak shows the difference in energy between the reactants

and the peak. This difference is called the activation energy. Highlight this as well.

a. Which graph has a higher activation energy? ___________________________

b. Explain why. ____________________________________________________

5. Infer: What do you think would happen in a reaction if there was not enough activation

energy available to cross the activation energy peak? __________________________

Which diagram below represents this situation? ______________________________

Diagram A Diagram B

1.

2.

3.

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Reviewing Potential Energy Diagrams

a) Fill in the blanks using the word bank below.

1. _____________measures the heat content.

2. ________________________ is the amount of stored energy at the start of the reaction.

3. ________________________ is the amount of stored energy at the end of the reaction.

4. The minimum amount of energy needed to initiate effective collisions is known as the

___________________________.

5. The _________________________ measures the heat content or change of enthalpy in the

chemical system.

Formula: ___________________________________

6. Highest point on the potential energy diagram that describes the unstable formation of the reacting

particles before an effective collision is known as the _________________________

7. ________________________________ describes the amount of stored energy at the activated

complex.

Word Bank: Activated Complex

P.E. of reactants

P.E. of products

Heat of reaction

Activation energy (Ea)

P.E. of the activated complex

∆H = Hproducts – Hreactants

Enthalpy

b) Label the Potential Energy Diagram Below:

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Name Date

Practice Reading and Drawing Potential Energy Diagrams

1. Answer the following questions based on the potential energy diagram shown here:

a. Does the graph represent an endothermic or exothermic

reaction? _______________

b. Label the potential energy of the reactants and products, the

activation energy of the forward reaction, ∆H, and the activated

complex.

c. Determine the heat of reaction, ∆H, (enthalpy change) for

this reaction. _______________

d. Determine the activation energy, Ea, for this reaction.

______________

e. How much energy is released or absorbed during the reaction?

____________________________

f. How much energy is required for this reaction to occur? ___________________________

2. Sketch a potential energy curve that is represented by the following values of ∆H and Ea: ∆H = -100 kJ and Ea = 20 kJ

You may make up appropriate values for the y-axis (potential energy). Is the curve endothermic or exothermic? ___________

3. Sketch a potential energy diagram for a general reaction A + B C + D iven that ∆H = 10 kJ and Ea = +40 kJ. You may make up appropriate values for the y-axis (potential energy). Is the curve endothermic or exothermic? ___________

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Name: ____________________ Date: _________________ Period: ______

Collisions Drive Reactions

Collision Theory Background Information:

In order for a reaction to occur, particles of the reactant must collide. Not

every collision will do. The colliding particles must approach each other at the

proper angle, the proper amount of energy and appropriate speed in order for a

reaction to occur. Such a collision is called an effective collision.

The greater the rate of effective collisions is, the greater the reaction rate is.

If all the particles shown on the reactant side of a balanced equation had to collide in order for a

reaction to occur, the reaction would not take place. As a result, chemical reactions occur by a series of

intermediate steps between the initial reactants and final products, each of which probably involves a

collision of only two particles.

This series of steps is called a reaction mechanism. The slowest step of the reaction mechanism is

called the rate-determining step.

Answer the questions below based on the reading above and on your knowledge of chemistry.

1. You are playing pool. You line up your cue, pull back, and shoot. Complete the following statement:

“Nothing will happen at all if the cue ball _________________________________.”

2. How is this similar to the requirements for the molecules of reactants to react with each other?

________________________________________________________________

________________________________________________________________

3. Examine the picture at right. Why isn’t the procedure pictured a good way to chop down a tree?

_______________________________________________________

How is this similar to the requirements for a chemical reaction to occur?

_______________________________________________________

_______________________________________________________

_______________________________________________________

4. Hydrogen gas and iodine vapor combine to form hydrogen iodide gas, as

shown in the equation: H2 + I

2 → 2 HI

Draw a diagram to show an orientation for the reactant molecules that WOULD produce an

effective collision and an orientation that would

NOT produce an effective collision. Orientation for Effective Collision Orientation for Ineffective Collision

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Collision Theory: How Do Reactions Occur?

Reactions only occur when there are EFFECTIVE COLLISIONS between reacting particles.

Effective Collisions Require:

1. ________________________________________________________

2. ________________________________________________________

3. ________________________________________________________

Practice Regents Questions

1. What is required for a chemical reaction to occur?

a. standard temperature and pressure

b. a catalyst added to the reaction system

c. effective collisions between reactant particles

d. an equal number of moles of reactants and products

2. A reaction is most likely to occur when reactant particles collide with

a. proper energy, only

b. proper orientation, only

c. both proper energy and proper orientation

d. neither proper energy nor proper orientation

3. Two reactant particles collide with proper orientation. The collision will be effective if

the particles have

a. high activation energy

b. high ionization energy

c. sufficient kinetic energy

d. sufficient potential energy

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Name: _______________________ Date: ______________

Aim:

What factors affect the rate of a chemical reaction?

Do Now: A “rate” is a measure of how much something changes within a

specified amount of time.

1. What units can be used to measure each of the following rates?

a. Car speed: ________ per _________

b. Plant growth: ________ per _________

c. Rusting: ________ per _________

2. Which of the above has the fastest reaction rate? ______________

3. Which of the above takes the longest reaction time? _________________

4. Based on the diagram below, is the rate of conversion of reactant to product

constant throughout the reaction? ____ How can you tell? ____________

_________________________________________________________

_________________________________________________________

Factors Affecting Rate of Reaction

1. __________________

2. __________________

3. __________________

4. __________________

5. __________________

(6. __________________)

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Name: ________________ Chemical Kinetics

Aim: _________________________________________________

Do Now: Which reaction rate factor does each diagram below represent?

1. _____________________________

In terms of collision theory, increasing ______________ will ______________

the rate of reaction because _______________________________________

_____________________________________________________________

_____________________________________________________________

2. _____________________________

In terms of collision theory, increasing ______________ will ______________

the rate of reaction because _______________________________________

_____________________________________________________________

_____________________________________________________________

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3. _____________________________

In terms of collision theory, increasing ______________ (which is the same as

decreasing __________________) will ______________ the rate of reaction

because ______________________________________________________

_____________________________________________________________

4. _____________________________

Pressure only affects the _____________ state of matter, because ______ and

________ are not compressible.

In terms of collision theory, increasing ______________ on a gaseous sample

(which is the essentially increasing __________________) will

______________ the rate of reaction because _________________________

_____________________________________________________________

Larger particles, less surface area,

fewer frequent effective collisions

Smaller particles, greater surface area,

more frequent effective collisions

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5. _____________________________

a) Which metal would react most vigorously with water?

Na(s) Fr(s) Ca(s) Sr(s) Li(s)

_______________________________________

_______________________________________

_______________________________________

b) Which substance would react fastest?

C6H12O6(s) C3H8(g) NaCl(s) NaCl(aq)

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

6. Presence of a Catalyst

Draw the effect of a catalyst on the potential diagram below:

Define “catalyst” using your glossary:

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

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Practice Regents Questions Collision Theory & Factors Affecting Rxn Rate

1. For a reaction at equilibrium, which change can increase the rates of the forward and

reverse reactions?

a) a decrease in the concentration of the reactants

b) a decrease in the surface area of the products

c) an increase in the temperature of the system

d) an increase in the activation energy of the forward reaction

2. Which statement explains why increasing the temperature increases the rate of a

chemical reaction, while other conditions remain the same?

a) The reacting particles have less energy and collide less frequently.

b) The reacting particles have less energy and collide more frequently.

c) The reacting particles have more energy and collide less frequently.

d) The reacting particles have more energy and collide more frequently.

3. A 5.0-gram sample of zinc and a 50.-milliliter sample of hydrochloric acid are used in a

chemical reaction. Which combination of these samples has the fastest reaction rate?

a) a zinc strip and 1.0 M HCl(aq)

b) a zinc strip and 3.0 M HCl(aq)

c) zinc powder and 1.0 M HCl(aq)

d) zinc powder and 3.0 M HCl(aq)

4. If the pressure on gaseous reactants is increased, the rate of reaction is increased

because there is an increase in the

a) activation energy

b) volume

c) concentration

d) heat of reaction

5. Given the reaction: CuSO4(s) ↔ Cu2+(aq) + SO2–

(aq)

The CuSO4(s) dissolves more rapidly when it is powdered because the increased surface

area due to powdering permits

a) increased solvent contact

b) increased solute solubility

c) the equilibrium to shift to the left

d) the equilibrium to shift to the right

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6. Which statement explains why the speed of some chemical reactions is increased when

the surface area of the reactant is increased?

a) This change increases the density of the reactant particles.

b) This change increases the concentration of the reactant.

c) This change exposes more reactant particles to a possible collision.

d) This change alters the electrical conductivity of the reactant particles.

7. For a given chemical reaction, the addition of a catalyst provides a different reaction

pathway that

a) decreases the reaction rate and has a higher activation energy

b) decreases the reaction rate and has a lower activation energy

c) increases the reaction rate and has a higher activation energy

d) increases the reaction rate and has a lower activation energy

8. Which potential energy diagram represents the change in potential energy that occurs

when a catalyst is added to a chemical reaction?

a) b)

c) d)

9. If a catalyst is added to a system at equilibrium and the temperature and pressure

remain constant, there will be no effect on the

a) rate of the forward reaction

b) rate of the reverse reaction

c) activation energy of the reaction

d) heat of reaction

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Name: _______________________ Date: ______________ Pd: ___ Chemical Kinetics

Aim: What are two characteristics of a spontaneous reaction?

Two factors are favored in nature to make a reaction occur spontaneously:

1. ___________________________________________________

2. ___________________________________________________

1.THE DRIVE TOWARD MINIMAL POTENTIAL ENERGY (ENTHALPY, ∆H)

Spontaneous Reactions

represent a drive toward ___________ potential energy & ____________ stability. Potential Energy Diagram Sketch Endothermic or Exothermic? ∆H Value

Practice Regents Questions:

1. Given the reaction at STP whereby solid NaOH(s) dissociates into its ions, the heat of

reaction (∆H) is

a. negative and the reaction is spontaneous

b. negative and the reaction is not spontaneous

c. positive and the reaction is spontaneous

d. positive and the reaction is not spontaneous

2. According to Reference Table I, which gas is formed from its elements by a spontaneous

reaction?

a. NO(g)

b. NO2(g)

c. CO2(g) d. C2H2(g)

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2.THE DRIVE TOWARD MAXIMUM DISORDER (ENTROPY)

Spontaneous reactions represent a drive toward maximum disorder. Entropy is a measure of the _______________ or ________________ of a system.

Spontaneous reactions favor ______________ entropy.

Positive ∆S represents an _____________ in entropy.

Describing Entropy (∆S) 1. Temperature

At higher temperatures, kinetic energy and randomness (entropy) ______________.

Ex: Which has higher entropy: CO2 at 27oC or CO2 at 80oC?

2. Phases of Matter

Most entropy Least entropy

___________ > ___________ > ___________ > ___________

Ex: For each phase change below, is entropy positive or negative?

Phase Change Entropy increase or decrease? Sign of ∆S: (+) or (-)

(g) (aq)

(s) (aq)

(l) (g)

(s) (l)

3. Type of Matter (Mixtures vs. Pure Substances)

Mixtures have ___________ entropy than pure substances.

Ex: Which has higher entropy: NaCl(s) or NaCl(aq)?

4. Type of Matter (Free Elements vs. Compounds)

Compounds have _________ entropy than the free elements of which they’re composed.

Ex: In terms of valence electrons, explain why sodium atom and chlorine atom have higher entropy than sodium chloride compound. ______________________________________________________________

5. Organization of Matter (# of Moles of Reactants & Products)

The side of the equation with the ___________ number of ____________ has the

greater amount of entropy.

Ex:

2CO(g) + O2(g) CO2(g) ∆S = ____

CaCO3(s) CaO(s) + CO2(g) ∆S = ____

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Review: Analyzing the Entropy of Different Reactions

Entropy is the degree of randomness in a substance. The symbol for change in entropy is ∆S.

Solids are very ordered and have low entropy. Liquids and aqueous ions have more entropy

because they move about more freely, and gases have the highest amount of entropy.

According to the Second Law of Thermodynamics, nature is always proceeding to a state of

higher entropy. When ∆S (entropy) is positive, entropy is increasing and the products have a

greater degree of randomness/disorder than do the reactants. Likewise, when ∆S (entropy) is

negative, entropy is decreasing and the products occupy less randomness or disorder.

Determine whether the following reactions show an increase or decrease in entropy. Also, indicate

whether the ∆S would be positive (+) or negative (-).

Chemical Reaction Entropy

(Increase/Decrease) ∆S

(+ or -)

Reason (#1-5 from notes)

1. 2KClO3(s) 2KCl(s) + 3O2(g)

2. H2O(l) H2O(s)

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

4. NaCl(s) Na+(aq) + Cl-(aq)

5. C(s) + O2(g) CO2(g)

6. 2N2O5(g) 4NO2(g) + O2(g)

7. KCl(s) KCl(l)

8. 2Al(s) + 3I2(s) 2AlI3(s)

9. 2NO(g) N2(g) + O2(g)

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Using your knowledge of chemistry and Reference Table I, answer the following questions:

1. Which requires less effort to maintain:

[ messy room / organized room ]

[ orderly classroom / chaotic classroom]

[ raked pile of leaves / scattered leaves ]

2. Based on the exercise on the previous page, a(n) [ increase / decrease ] in entropy is favored

for most chemical or physical changes.

3. Take a look at Table I. What is mostly favored, [ endothermic / exothermic ] reactins.

Therefore, in nature, an [ endothermic / exothermic ] reaction is favored.

4. To summarize, reactions tend to proceed towards [ lesser / greater ] enthalpy (∆H),

and [ lesser / greater ] entropy (∆S). This results in a [ spontaneous / non-spontaneous ]

chemical reaction.

5. Which term is defined as a measure of the disorder of a system?

(1) heat (2) entropy (3) kinetic energy (4) activation energy

6. Which of the following processes has a negative ∆𝑆?

(1) evaporating 50 grams of a liquid

(2) raising the temperature of water from 250K to 383K

(3) freezing 75 mL of a liquid

(4) none of the above

7. A reaction will be spontaneous if it results in products that have

(1) lower potential energy and less randomness

(2) lower potential energy and more randomness

(3) greater potential energy and less randomness

(4) greater potential energy and more randomness

8. Which statement describes this phase change?

C6H4Cl2(s) + energy → C6H4Cl2(g)

(1) It is endothermic, and entropy decreases.

(2) It is endothermic, and entropy increases.

(3) It is exothermic, and entropy decreases.

(4) It is exothermic, and entropy increases.

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Name: _______________________ Date: ______________ Pd: ___ Chemical Kinetics

Aim: How do enthalpy and entropy determine reaction spontaneity? Whether a reaction proceeds spontaneously or not depends on the balance between two natural

tendencies:

[1] The drive toward greater stability (reduced potential energy), i.e. (-)∆H;

[2] The drive toward less organization (increased entropy), i.e. (+)∆S

High entropy is favored by increased temperature. The Gibbs free energy change (∆G) predicts whether

or not a reaction is spontaneous. It takes into acount the change in enthalpy and the change in entropy.

The Gibbs free energy change is the difference between the energy change (∆H) and the product

of the absolute or Kelvin temperature (T) and the entropy change (∆S), according to the equation

below:

For a system at equilibrium, ∆G = 0. In order for a system to change spontaneously, the resulting ∆G

must be negative. If the drive toward lower energy and higher entropy cannot be satisfied at the same

time, the type of change that will be favored will depend on the temperature. At low temperatures, the

term T∆S will be small, and ∆H will have the greatest effect on the free energy. At high temperatures,

the term T∆S will be large, and ∆S will have the greatest effect on the free energy.

Based on the reading above, fill in the table below and answer the questions that follow

Reaction Conditions Is the reaction spontaneous? [-∆G]

(Always, Never, At High Temps, or At Low Temps) Temperature ∆H ∆S

High + -

High + +

High - -

High - +

Low + -

Low + +

Low - -

Low - +

Try This:

1. The entropy change for the following reaction at 298 K is 3.0 J/mol·K, and the enthalpy change is –394

kJ/mol. Calculate the Gibbs free energy change and determine whether the reaction will occur spontaneously.

C(s) + O2(g) CO2(g)

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Transition State Theory What is the Activated Complex (a.k.a. The Transition State)?

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During any chemical reaction, particles (atoms, molecules, and/or ions) are rearranged to form

new substances by breaking old bonds and forming new bonds. Bond breaking requires energy,

while bond making releases energy. Even exothermic reactions, such as burning wood, need energy to get started to break existing bonds in reacting particles. The energy required to

initiate a chemical reaction is called activation energy. Activation energy comes from the

collisions between reacting molecules, as well as additional input of energy from sources such as

a spark, a match, or other heat source and is used to form an unstable, high-energy activated complex. The high-energy activated complex is so unstable, it quickly falls apart to form the

products. Because the activated complex lasts only a short time, it is also called a transition

state complex. According to transition state theory, during a chemical reaction, intermediate

products, known as the activated complex, form that exist for only brief periods of time while

the atoms rearrange themselves.

Answer the questions below based on the reading above and on your knowledge of

chemistry.

1. Why is it necessary to supply energy in the form of a spark to ignite the gasoline in an

automobile engine if gasoline releases energy when it burns?

_______________________________________________________________________

2. According to collision theory, where does the activation energy during a reaction come from?

_______________________________________________________________________

3. According to transition state theory, what is activation energy used for?

_______________________________________________________________________

_______________________________________________________________________

4. What is an activated complex?

_______________________________________________________________________

_______________________________________________________________________

a) Why does it last only a short time?

__________________________________________

b) Why it is it considered unstable?

____________________________________________

____________________________________________

______________________________________

c) What forms from the activated complex?

__________________________________________

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d) How does the potential energy of the activated complex compare to that of the

reactant or the product?

__________________________________________________________________

__________________________________________________________________

Practice Regents Questions

1. A piece of Mg(s) ribbon is held in a Bunsen burner flame and begins to burn according to

the equation: 2Mg(s) + O2 (g) → 2MgO(s). The reaction begins because the reactants

a. are activated by heat from the Bunsen burner flame

b. are activated by heat from the burning magnesium

c. underwent an increase in entropy

d. underwent a decrease in entropy

2. The energy needed to start a chemical reaction is called

a. potential energy

b. kinetic energy

c. activation energy

d. ionization energy

3. In the potential energy diagram below, which letter represents the potential energy of

the activated complex? _____