KINETICS and EQUILIBRIUMKINETICS and EQUILIBRIUM

I. Factors that Affect the Rate of Reaction (5)II. Heat of Reaction, ∆HIII. Spontaneous ReactionsIV. Equilibrium

Chapter 7

KINETICS refers to the rate and mechanism of reactions.

COLLISION THEORYCOLLISION THEORY

Factors that Affect the Rate of a Reaction

1. concentration of reactants(pressure for gases)

2. temperature3. surface area4. nature of reactants

– ionic compounds react quickly

5. catalyst– increase rate of reaction by lowering the

ACTIVATION ENERGY

• Every substance has potential energy/ heat content.• ∆H, the heat of reaction, is the amount of heat released or absorbed in a

chemical reaction.

∆H = Hproducts – Hreactants

EXOTHERMIC REACTION• heat is released; products have less P.E. (heat) than reactants • ∆H is NEGATIVE; feels HOT/WARM

ENDOTHERMIC REACTION• heat is absorbed, products have more P.E. (heat) than reactants• ∆H is POSITIVE; feels COLD

HEAT OF REACTION, ∆HHEAT OF REACTION, ∆H

reactants products

Given the reaction at 25°C:

Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (aq)

The rate of this reaction can be increased by using 5.0 grams of powdered zinc instead of a 5.0-gram strip of zinc because powdered zinc has

A catalyst increases the rate of a chemical reaction by

DO NOW

(d) more zinc atoms(b) lower concentration

(c) more surface area(a) lower kinetic energy

raising the concentration of the reactants(d)

raising the temperature of the reactants(c)

lowering the potential energy of the products(b)

lowering the activation energy of the reaction (a)

Explain your answers!

Reaction # 1

2H2 + O2 2H2O + 571.6 KJ

Reaction # 2

N2 + O2 + 182.6 KJ 2NO

HEAT OF REACTION, ∆HHEAT OF REACTION, ∆H

reactants products

heat

heat

reactants products + heat

reactants + heat products

exothermic

endothermic

A hot pack contains chemicals that can be activated to produce heat.

A cold pack contains chemicals that feel cold when activated.

1) Based on energy flow, state the type of chemical change that occurs in a hot pack.

2) A cold pack is placed on an injured leg. Indicate the direction of the flow between the leg and the cold pack.

3) What is the Law of Conservation of Energy? – Describe how this law applies to the chemical reaction that

occurs in the hot pack.

4) Identify a reactant in Table I that, when mixed with water, can be used for a cold pack.

A + B C + heatEXOTHERMIC∆H is NEGATIVE.

A. PE of reactantsB. PE of productsC. PE of activated

complexD. activation energy

(for forward reaction, Eact)

E. Heat of Reaction, ∆H, Enthalpy

F. activation energy for reverse reaction

POTENTIAL ENERGY DIAGRAMSPOTENTIAL ENERGY DIAGRAMS

Reaction Coordinate

reactants

productsAB

C

D

E

F

transition stateactivated complex

POTENTIAL ENERGY DIAGRAMSPOTENTIAL ENERGY DIAGRAMS

A

C + heat A + BENDOTHERMIC∆H is POSITIVE.

A. PE of reactantsB. PE of productsC. PE of activated

complexD. activation energy

(for forward reaction, Eact)

E. Heat of Reaction, ∆H, Enthalpy

F. activation energy for reverse reaction

B

C

D

reactants

products

transition stateactivated complex

E

F

PE DIAGRAMS with PE DIAGRAMS with CATALYSTCATALYST

SPONTANEOUS REACTIONSSPONTANEOUS REACTIONS

What makes a reaction SPONTANEOUS?

NOT SPONTANEOU

S

ENTROPY

ENTHALPY

depends on the temperatureSPONTANEOUS

decreasing

exothermic

increasing

s → l → g

more

randomness

increasing

endothermic

decreasing

g → l → s

lessrandomness

endothermic

decreasing

g → l → s

lessrandomness

exothermic

increasing

s → l → g

morerandomness

1) What does each arrow represent?

2) Which numbered quantities would change if a catalyst were added?

3) Show how the PE diagram would look if a catalyst were added.

DO NOW

Given the following equation, which

statement is true?

N2(g) + 3H2(g) 2NH3(g) – 91.8 kJ

The sign of ∆H is negative, and the reaction is endothermic.

(d)

The sign of ∆H is negative, and the reaction is exothermic.

(c)

The sign of ∆H is positive, and the reaction is endothermic.

(b)

The sign of ∆H is positive, and the reaction is exothermic.

(a)

1) The letter B represents which chemical formula(s) in the equation?

2) If 682.2 kJ are absorbed, how many moles of C2H2(g) are produced?

3) Describe how the PE diagram will change if a catalyst is added.

1) Is the reaction exothermic or endothermic? Explain.

2) Identify each of the numbered arrows on the graph.

• PE of reactants• PE of products• PE of activated complex• activation energy• heat of reaction• Eact of reverse reaction

3) Which numbered quantities would change if a catalyst were added?

E.C.

QUIZ

reactants absorb and release energy

A. PHYSICAL EQUILIBRIUM1. phase equilibrium2. solution equilibrium

(saturated solution)

B. CHEMICAL EQUILIBRIUMwhen the rates of the forward and reverse reactions are equal in a chemical reaction

(The forward and reverse reactions occur at the same rate.)

The concentrations of the reactants and products remain CONSTANT (but are not necessarily equal).

dynamic equilibriumN2 + 3H2 2NH3 + heat

EQUILIBRIUMEQUILIBRIUM

forwardreverse

When a system at equilibrium is subjected to a stress (disturbed), the equilibrium will shift in the direction that relieves the stress/ re-establishes the equilibrium.

STRESSES

1. change in concentration

2. change in pressure (gases)

3. change in temperature

– The addition of heat increases the rates of the forward and reverse reactions.

– However, it will favor the ENDOTHERMIC reaction more.– The removal of heat favors the EXOTHERMIC reaction.

4. catalysts– speed up both the forward and reverse reactions (at the same rate)– produce no change in concentration

LE CHATELIER’S PRINCIPLELE CHATELIER’S PRINCIPLE

increase conc. of A

increase conc. of D

decrease conc. of B

decrease conc. of C

increase pressure

decrease pressure

increase temp.

decrease temp.

catalyst

AA(s)(s) + 2B + 2B(g)(g) CC(s) (s) + D+ D(g) (g) + heat+ heat stress

volume of gas must decrease

volume of gas must increase

NO SHIFT NO SHIFT

LE CHATELIER’S PRINCIPLELE CHATELIER’S PRINCIPLE

The rates of both the forward and reverse reactions are increased by the same amount.

NO SHIFTadd a catalyst

more heat/ energy needs to be produced to make up for the loss

towards heat/ energy

exothermic reaction is favoreddecrease temperature of system

extra heat/ energy must be used up

away from heat/ energy

exothermic reaction is favoredincrease temperature of system

for gas: pressure decrease = volume increase

towards more moles of gas

decrease pressure of system

for gas: pressure increase = volume decrease

towards fewer moles of gas

increase pressure of system

need to produce more of substance to make up for what was removed

towards substancedecrease concentration of a substance

extra concentration needs to be used up

away from substanceincrease concentration of a substance

WHY?SHIFTSTRESS

H2(g) + Cl2(g) 2HCl(g)

1. When the concentration of H2 is increased, what happens to the concentrations of Cl2 and HCl? Explain.

2. When the concentration of HCl is decreased, what happens to the concentrations of H2 and Cl2? Explain.

3. How does an increase in pressure affect this equilibrium? Explain.

4. How does a decrease in pressure affect this equilibrium? Explain.

DO NOW

activated complex

reactants

products

N2(g) + 3H2(g) 2NH3(g) + 22.0 kcal

10. Decrease press.

9. Increase press.

8. Decrease temp

7. Increase temp

6. Remove NH3

5. Remove H2

4. Remove N2

3. Add NH3

2. Add H2

1. Add N2

[NH3][H2][N2]ShiftStress

N2(g) + 3H2(g) 2NH3(g) + 22.0 kcal

10. Decrease press.

9. Increase press.

8. Decrease temp

7. Increase temp

6. Remove NH3

5. Remove H2

4. Remove N2

3. Add NH3

2. Add H2

1. Add N2

[NH3][H2][N2]ShiftStress_____

_____

_____

_____

_____

_____

CO2 is added

CO is added

O2 is added

CO is removed

O2 is added

pressure is increased

pressure is decreased

temp. is increased

temp. is decreased

catalyst is added

2CO2CO2(s)2(s) + heat + heat 2CO2CO(s) (s) + O+ O2(g)2(g)stress

2CO2CO(g)(g) + O + O22 2CO 2CO2(g)2(g)

Describe the effects of the following stresses on the system in equilibrium.

1) concentration of CO is increased2) concentration of O2 is decreased3) pressure is decreased4) pressure is increased

Which way will the equilibrium shift?

DO NOW

Given the reaction:

N2(g) + O2(g) + 182.6 kJ 2NO(g)

Which change would cause an immediate increase in the rate of the forward reaction?

(1) increasing the concentration of NO(g)

(2) increasing the concentration of N2(g)

(3) decreasing the reaction temperature

(4) decreasing the reaction pressure

DO NOW

2POCl2POCl3(g)3(g) + energy + energy 2PCl 2PCl3(g) 3(g) + O+ O2(g)2(g)

Which changes occur when O2(g) is added to the system?

1) The equilibrium shifts right and [PCl3] increases.2) The equilibrium shifts right and [PCl3] decreases.3) The equilibrium shifts left and [PCl3] increases.4) The equilibrium shifts left and [PCl3] decreases

DO NOW

12.6 kcal + H2(g) + I2(g) 2HI

10. Decrease press.

9. Increase press.

8. Decrease temp

7. Increase temp

6. Remove HI

5. Remove I2

4. Remove H2

3. Add HI

2. Add I2

1. Add H2

[HI][I2][H2]ShiftStress

12.6 kcal + H2(g) + I2(g) 2HI

10. Decrease press.

9. Increase press.

8. Decrease temp

7. Increase temp

6. Remove HI

5. Remove I2

4. Remove H2

3. Add HI

2. Add I2

1. Add H2

[HI][I2][H2]ShiftStress_____

_____

_____

_____

_____

_____

=

=

NO CHANGE

REMAINS THE SAME

BaSO4(s) Ba2+(aq) + SO4

2-(aq)

AgBr(s) Ag+(aq) + Br(aq)

COMMON ION EFFECTCOMMON ION EFFECT

Add so42-…cuso4…nacl

equilibrium cannot be established

1) a GAS is formed, which leaves the system

2) an unionized product, like WATER, is formed

3) an insoluble product, a PRECIPITATE, is formed

H2CO3 H2O + CO2 ↑

HCl + NaOH NaCl + H2O

NaCl + AgNO3 NaNO3 + AgCl ↓

REACTIONS that go to REACTIONS that go to COMPLETIONCOMPLETION

Carla the chemistry student has landed her first job working for a manufacturer of ammonia. Ammonia, NH3(g), is prepared

from N2(g) and H2(g). The more

ammonia that is produced, the

greater the company’s profits, so

Carla’s first challenge is to

set the reaction conditions to make as much NH3 as possible.

Can you give Carla ideas to increase the production of NH3?

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

QUIZ

2SO2SO2(g) 2(g) + O+ O2(g) 2(g) 2SO 2SO3(g) 3(g) + heat+ heat

For each of the following stresses, state in which direction the equilibrium will shift and what will happen to the concentration of SO2. Explain.

1) concentration of O2 is decreased

2) pressure is decreased

3) temperature is decreased

4) a catalyst is added

QUIZ

8. Decrease press

7. Increase press

6. Decrease temp

5. Increase temp

4. Add H+

(removes OH+)

3. Add KOH (adds OH-)

2. Add NaCl (adds Na+)

1. Add NaOH

[OH-][Na+]NaOH(s)ShiftStress

NaOH(s) Na+(aq) + OH-

(aq) + 10.6 kcal

NaOH(s) Na+(aq) + OH-

(aq) + 10.6 kcal

8. Decrease press

7. Increase press

6. Decrease temp

5. Increase temp

4. Add H+

(removes OH+)

3. Add KOH (adds OH-)

2. Add NaCl (adds Na+)

1. Add NaOH

[OH-][Na+]NaOH(s)ShiftStress_____

_____

_____

_____

NO EFFECT …………………… REMAINS THE SAME

In each of the beakers shown below, a 2.0-cm strip of magnesium ribbon reacts with 100-mL of HCl under the conditions shown.

In which beaker will the reaction occur at the fastest rate?

0.1 M HCl20°C

1.0 M HCl20°C

0.1 M HCl50°C

1.0 M HCl50°C

Beaker A Beaker B Beaker C Beaker D

(1) (2) (3) (4)

Given the equilibrium equation:

KNO3(s) + 34.89 kJ K+(aq) + NO3

-(aq)

1) Describe, in terms of Le Chatelier’s Principle, why an increase in temperature increases the solubility of KNO3.

2) The equation indicates that KNO3 has formed a saturated solution.

Explain, in terms of equilibrium, why the solution is saturated.

H2O

A student using a Styrofoam cup as a calorimeter added a piece of metal to distilled water and stirred the mixture. The student’s data is shown below.

a) the initial temperature of 50.0 g of water 25°C

b) the initial temperature of 20.0 g of metal 100°C

c) the final temperature of the water and metal 32.0°C

How much heat is lost or gained– by the water?– by the metal?

Data

The water gained 350 calories of heat and the metal lost 350 calories of heat.