Unit 5

1

This Unit covers Chapters 12, 13, and 15 (sections 1-3) Suggested practice problems: Chapter 12: 1-12, 15-20, 27-32, 43-46, 49-68 Chapter 13: 1-18, 31-50, 69-74, 77-78, 81, 83-86, 88, 91-94, 99-102 Chapter 15: 3-10, 13-22, 29-34, 39-46, 48-50, 53-68, 70, 75-78 Rates of Reactions Demo: Use models to represent the following reaction:

2H2 + O2 → 2H2O For the reaction to occur, bonds must first be _____________, and then the new ____________ are formed.

Breaking bonds: Forming bonds:

Endothermic and Exothermic Reactions Ea: Activation Energy-the amount of ____________ needed to ___________

the necessary bonds

The energy to break bonds comes from:

Not all collisions cause a reaction, those that do are called:

↑ E

↑E

2

Effective Collisions To be effective the collision between molecules has to have

1.

2. The higher the Ea the slower the reaction rate. Why?

Factors that affect the rate of a reaction 1. Nature of reactants

Demo: Compare the rates of the following reactions

a. 5H2O2 + 2 KMnO4 + 3H2SO4 → 5O2 + 2MnSO4 + K2SO4 + 8H2O b. 5H2C2O4 + 2 KMnO4 + 3H2SO4 → 10CO2 + 2MnSO4 + K2SO4 + 8H2O

Which reaction has a faster rate? Which has a higher Ea?

3

2. Size and Physical States of Reactants

Demo: Drop whole and crushed Alka-Seltzer tablets into beakers of water.

Which tablet reacted fastest? Why? 3. Concentration of Reactants

Demo: Compare the rates of the following reaction when 1 M HCl and 6 M HCl are used.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Which concentration reacted fastest? Why?

4. Temperature

Demo: Drop whole Alka-Seltzer tablets into hot and cold water

Which temperature reacted fastest? Why? 5. Catalyst A chemical that changes the rate of a reaction without being used up

Demo: Add MnSO4 to reaction b above.

What happed to the rate?

How does a catalyst work?

4

Equilibrium The Bead Game 2 green red + blue Instructions: Place 50 green beads in the plastic box. Simulate a collision by choosing two beads. Then apply the following rules:

a. If both beads are green, remove them and replace with one red and one blue b. If one is red and the other blue, remove them and replace with 2 green c. If the beads are any other combination, don’t do anything.

Number of Collisions Number of Green Number of Red

0 25 50

75 As the game continues what happens to the possibility that 2 green will react?

How about a red and blue? Use the computer to play for a long time.

Even after _______ turns are all the green gone?

Instead of all the green being converted to red and blue a “stale-mate” condition called __________________ is produced, where both reactants and products are present. Important Properties of a reaction at equilibrium

1. The reaction __________ stop. 2. The amounts of product and reactant are ___________. 3. If the reaction does not stop, how can the amount of product and reactant remain

constant? So, what is “equal” at equilibrium?

5

Reversible Reactions Type of arrow: Example: 2NOBr(g) 2NO(g) + Br2(g) What if we want to know how much bromine is produced once we reach equilibrium. Can we use the mole map? Why? Equilibrium Constants (K) aA + bB cC + dD Where the lowercase letters are the __________

K =

[ ] = Note: We always put the __________ on the top and the ___________ on the bottom When we calculate equilibrium constants we have to look at the state the reactants and products are in. We only use ______ and ________ in the equilibrium constant expression. So what do we do if we have a solid or liquid? What units does K have? Example 1: Write the expression for the equilibrium constant for the reaction above Example 2: If the concentrations are as follows, calculate K [NOBr] = 0.015 [NO] = 0.23 [Br2] = 0.046 Example 3: Using the K calculated in example 2, calculate the [NO] if the other

concentrations are as follows. [NOBr] = 0.27 [Br2] = 0.016

6

Practice Problems

H2(g) + CO2(g) H2O(g) + CO(g) 1. Write the expression for the equilibrium constant and calculate it’s value if the

concentrations are as follows [H2] = 1.83 [H2O] = 7.17 [CO2] = 7.31 [CO] = 2.04

2. Using the K found above determine the [CO] if the concentrations of the other gasses are as follows

[H2] = 2.78 [H2O] = 5.74 [CO2] = 4.94

2NOCl(g) 2NO(g) + Cl2(g)

3. Write the expression for the equilibrium constant and calculate it’s value if the concentrations are as follows

[NOCl] = 7.14 [NO] = 1.81 [Cl2] = 2.47

4. Using the K found above, determine the [NOCl] if the concentrations of the other gasses are as follows

[NO] = 4.87 [Cl2] = 7.01

7

CO(g) + 2H2(g) CH3OH(l)

5. Write the expression for the equilibrium constant and calculate it’s value if the concentrations are as follows

[CO] = 3.56 [H2] = 1.95 6. Using the K found above, determine the [H2] if the concentrations of the other gas is as

follows [CO] = 8.74

What does K tell us? Large K (K > 1) More_________, less ___________ at equilibrium Small K (K < 1) More_________, less ___________ at equilibrium What relationship does K have with the rate of a reaction? Le Chatelier’s Principle At equilibrium the rates of the forward and reverse reactions are equal, so the concentration of the reactants and products_______________________. But what happens if we do something?

Answ

ers

1. 1.0

9 2.

2.61

3.

0.15

9

4.

32.3

5

. 0.

0739

6.

1.2

4

8

Demo: Make a solution of chromate and dichromate ions.

2CrO42- + 2H3O+ Cr2O7

2- + 3H2O

Color: _________ __________ Add some H3O+, what color does the solution turn? Add some base (which removes the H3O+), what color does the solution turn? Remember the bead game; imagine the box at equilibrium with 2000 green, 1500 red, and 1500 blue. If we added 2000 more green beads what would happen to the chance that you would pick 2 green beads? What would happen to the chance that you would pick a red and blue?

Are the rates of the forward and reverse reaction still equal?

What will happen as the game is played?

Let the computer play the game

Color Number at 1st

equilibrium state Number Added

Number at 2nd equilibrium state

Green 2000 2000

Red 1500 0

Blue 1500 0 Does the game come to equilibrium again? How? How is this equilibrium state different from the first? Le Chatelier’s Principle: When stress is applied to a system at equilibrium the system

__________ to relieve some of the stress. Le Chatelier’s Principle is like:

9

Other factors beside adding or removing reactants or products can shift the reaction. Temperature Exothermic reaction- ________ heat A B Endothermic reaction- __________ heat A B Pressure (Volume) 2NOBr(g) 2NO(g) + Br2(g) If the pressure is increased by decreasing the volume the reaction will shift toward the side with the ________ number of moles of ______ What if the NO was a liquid and the pressure was increased?

10

Practice Problems 2NO(g) + O2(g) 2NO2(g) + heat Which direction (toward reactants, toward products, neither direction) will the equilibrium shift when

1. The temperature is raised

2. O2 is added

3. The pressure is increased

4. NO2 is removed

5. The temperature is lowered

6. NO is added

7. NO2 is added

8. The pressure is decreased

9. O2 is removed

10. NO is removed

11. A catalyst is added

Answ

ers

1. Re

acta

nts

2. Pr

oduc

ts

3.

Prod

ucts

4.

Pr

oduc

ts

5.

Prod

ucts

6.

Pr

oduc

ts

7.

Reac

tant

s 8.

Reac

tant

s 9.

Re

acta

nts

10.

Reac

tant

s 11.

Neith

er

11

Acids and Bases Naming Acids There are two types of acids 1. Binary Hydrogen bonded to a Group VIA element other than ______ or to a Group

VIIA element 2. Oxoacids (Ternary) Consist of three elements, hydrogen, oxygen, and (usually) a

_____________ Rules

acid ending of anion prefix ending

binary -ide hydro -ic

oxo -ate -ic

oxo -ite -ous

Name the following acids HF HCl H3PO4 H2CO3 HClO4 HClO3 HClO2 HClO HC2H3O2 HCN H2SO3 H2SO4 Naming Bases Most common bases are ionic compounds, and are named as such. Examples: NaOH CaCO3 Al(OH)3 Properties of Acids • ________ taste

Vinegar (acetic acid) Lemon (citric acid)

• Change colors of many indicators

Litmus Phenolphthalein

12

• Aqueous solutions of acids are electrolytes Strong acids are ________ electrolytes Weak acids are ______ electrolytes

Properties of Bases • ______ taste • Slippery feeling

Soap (weak base) Bleach (strong base)

• Change colors of many indicators

Litmus Phenolphthalein

• Aqueous solutions conduct electricity

Usually __________ electrolytes There are 3 main definitions of acids and bases; Arrhenius, Brønsted-Lowry, and Lewis. We are going to learn about the ______________ and _________________ definitions. Arrhenius Theory Acid- Substance that contains _______ and produces ______ ions in aqueous solution

Example: HCl(aq) → H+(aq) + Cl-(aq)

Base- Substance that contains the OH (hydroxyl) group and produces _____ ions in aqueous

solution

Example: NaOH(s) → Na+(aq) + OH-

(aq) Hydronium Ion Arrhenius described H+ ions in water as bare ions, but we now know that they are hydrated (attached to _______) in aqueous solution

H+(aq) + H2O(l) H3O+

(aq) The “more correct” Arrhenius definition of an acid:

Substance that contains hydrogen and produces hydronium, H3O+, in aqueous solution

13

Brønsted –Lowry Theory (The one we use most of the time) The Arrhenius theory only works when we are in __________ solution so Brønsted and Lowry independently expanded the Arrhenius theory Acid-A proton ________ Proton: Base-A proton ________ An acid-base reaction is the _____________ of a proton (H+) from an acid to a base When an acid gives up a proton it becomes a base-called a _____________ ________ Example: What is the conjugate base of HCl?

What is the conjugate base of H2SO4? When a base gains a proton it becomes an acid-called a _____________ ________ Example: What is the conjugate acid of NH2

-

What is the conjugate acid of CO32-?

Conjugate acids and bases In reactions we can identify the acid, base, and the conjugate acid and base.

HF(aq) + H2O(l) H3O+(aq) + F-

(aq)

Acid: Conjugate Acid:

Base: Conjugate Base:

14

Practice Problems

1. Give the conjugate acid for each of the following Brønsted-Lowry bases a. NH3

b. PO43-

c. ClO3-

d. HCO3-

2. Give the conjugate base for each of the following Brønsted-Lowry acids

a. H2S

b. HCO3-

c. HNO3

d. NH4+

3. Identify the acid, base, conjugate acid, and conjugate base for each of the following

reactions. a. NH2

-(aq) + H2O(l) → NH3(aq) + OH-

(aq)

b. H2O(l) + H2C2O4(aq) → HC2O4- + H3O+

(aq)

c. H3O+(aq) + HPO4

2-(aq) → H2PO4

-(aq) + H2O(l)

d. HC2O4-

(aq) + CO32-

(aq) C2O42-

(aq) + HCO3-

(aq)

e. H2O(l) + PH4+

(aq) PH3(aq) + H3O+(aq)

15

f. CN-(aq) + NH4

+(aq) HCN(aq) + NH3(aq)

Acid Strength Strong acids ionize completely (they are _________ electrolytes) in aqueous solution Weak acids only partially ionize (they are ________ electrolytes) in aqueous solution Strong acids produce ________ conjugate bases. Strong bases produce ________ conjugate acids. Why?

Answ

ers

1.

a.

NH4+

b. HP

O 42-

c.

HClO

3 d.

H 2CO

3 2.

a. HS

-

b. CO

32-

c. NO

3-

d. NH

3

16

Ka Remember that strong acids react _____________, but weak acids only ___________ react. So if we place a weak acid in water we will have a ________________ reaction and eventually a system at ________________. Example: HA(aq) + H2O(l) H3O+

(aq) + A-(aq)

Where HA is any ______ and A- is its ____________ _____

The equilibrium constant for this reaction is: K = Ka = Ka is defined as the acid dissociation constant, and is the equilibrium constant for a weak acid in water. Why don’t we use a Ka for strong acids? What is the relationship between Ka and acid strength? Example: Write the expression for Ka for the following weak acids:

1. H2C2O4(aq)

2. HCO3-

(aq)

3. NH3(aq)

4. H2PO4-

(aq)

17

Reactions between acids and bases

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq) Strong Acid + Strong Base → Water + A Salt

This is called a ____________________ reaction. A common use of neutralization reactions is ________________. Excess HCl in your stomach causes heartburn and antacids are ________ that react with the HCl to neutralize the acid and relieve the heartburn. Example: Look at the active ingredients of some antacids

Antacids Active Ingredients Antacids Active Ingredients

Rolaids Alka-Seltzer

Maalox Milk of Magnesia

Tums Mylanta

Self Ionization of Water

H2O(l) + H2O(l) H3O+(aq) + OH-

(aq) This reaction occurs _____________________ (in very small amounts) in water In this reaction one water acts as an acid and the other acts as a base. Water is amphiprotic

Substances that are amphiprotic can act as ___________ an acid or a base.

K = Kw = = 1 x 10-14 (exact number)

Kw is called the ion-product of water

Example: What is the [OH-] if the [H3O+] = 4.82 x 10-5?

18

pH and pOH The [H3O+] of any aqueous solution is a very important characteristic, and we often need to talk about it. It is inconvenient to talk about the concentration in units such as 4.50 x 10-12 M or numbers similar to this form. So scientist defined a new number called _____ to talk about the concentration in a more convenient form. The formula for pH is:

pH = Example 1: What is the pH of a solution if the [H3O+] = 1 x 10-8? Example 2: What is the pH of a solution if the [H3O+] = 3.65 x 10-12? Remember that the “antilog” is 10x. So, if we know pH we can calculate the [H3O+] using the formula [H3O+] = 10-pH Example 3: What is the [H3O+] if the pH = 3.5? Example 4: What is the [H3O+] if the pH is 10.6? We can also use pOH to talk about the [OH-]: pOH = and [OH-] = 10-pOH We can use the properties of logs and the Kw to get the formula: pH + pOH = 14

19

Acidic and Basic Solutions Demo: Use a pH meter to measure the pH of some household chemicals. Then calculate the

pOH and [H3O+] and [OH-]

Substance pH pOH Acid or Base [H3O+] [OH]

Coke

7-UP

Drano

Lime-A-Way

Aspirin

Ammonia

Baking Soda

Mylanta

Toilet Cleaner

Clorox

Tide

__________solution [H3O+] [OH-]

__________solution [H3O+] [OH-]

pH

14 0 7 7 0 14

pOH

__________solution [H3O+] [OH-]

20

Buffers Example: Add HCl and NaOH to water and phosphate buffer and record what happens to

the pH.

Solution pH pH with Acid added pH with Base added

Pure Water

Phosphate Buffer Buffer a solution whose pH doesn’t ___________ very much when ________ or

______ ions are added.

How are they made? How do they work?

21

Buffer Capacity-you _____________overload a buffer Blood Buffers

pH of blood: Change > ______ Pathological pH <______ or > ______ you die Made from:

Practice Problems

1. Calculate the [OH-] if the [H3O+] is a. 6.29 x 10-4

b. 8.20 x 10-7

c. 7.18 x 10-2

2. Calculate the pOH of a solution if the [OH-] is:

a. 7.15 x 10-5

b. 2.78 x 10-2

c. 4.27 x 10-12

3. Calculate the [OH-] if the pOH is:

a. 1.75

b. 5.61

c. 6.90

d. 9.45

4. Calculate the pH of a solution if the [OH-] is:

a. 8.14 x 10-5

b. 1.78 x 10-10

c. 3.47 x 10-1

22

5. If the [OH-] = 1.89 x 10-8 calculate the a. pOH

b. pH

c. [H3O+]

6. If the [H3O+] = 7.13 x 10-4 calculate the

a. pH

b. pOH

c. [OH-]

7. If the pH = 5.81 calculate the

a. pOH

b. [H3O+]

c. [OH-]

8. If the pOH = 1.82 calculate the

a. pH

b. [H3O+]

c. [OH-]

Answ

ers

1.

a.

1.59

x 10

-11

b. 1.2

2 x

10-

8 c.

1.39

x 10

-13

2.

a.

4.15

b.

1.56

c. 11.4

3.

a. 0.

0178

b.

2.45

x 10

-6

c. 1.2

6 x

10-

7 d.

3.5

5 x

10-

10

4.

a.

9.91

b.

4.25

c.

13.5

5.

a. 7.

72

b. 6.

28

c. 5

.29 x

10-

7 6.

a. 3.

15

b. 10

.85

c. 1.4

0 x

10-

11 7.

a. 8.1

9 b.

1.55

x 10

-6

c. 6.

46 x

10-

9 8.

a. 12

.18

b. 6.

61 x

10-

13

c. 0.

015

1

23

Nuclear Chemistry The chemistry we have talked about so far has dealt with what happens _________ the nucleus. Remember that there are 3 particles that make up an atom. The _________ and ___________ reside inside the nucleus while the _________ (which are responsible for ions, bonding, reactions, electricity, light, and magnetism) reside outside the nucleus. Nuclear chemistry deals with what happens _________ the nucleus. Nuclear chemistry was “discovered” in the late ________ century and was studied by Becqueril, Pierre and Marie Curie, and Rutherford. Remember that each element has a number of __________. Some isotopes are stable and some are not, those isotopes that are unstable will emit radiation to become stable. These isotopes are called ______________ Types of Radiation Alpha: 42He 238

92U → 23490Th + 42He 210

84Po → + 42He For a nuclear reaction to be balanced the ________ of the mass and atomic numbers must be __________ on the reactant and product side Beta: 0-1e 3

1H → 32He + 0-1e 13153I → + 0-1e

Gamma: γ 40

19K → 4019K + γ 99

43Tc → + γ Positron: 0+1e 28

15P → 2814Si + 0+1e 42

21Sc → + 0+1e All radiation occurs at a ____________, set rate. We _____________ speed up or slow down radioactive decay. Our way of measuring the rate of radioactive decay is the __________. Half-life is defined as the time it takes for ½ of any sample of radioactive material to decay. The half-life for different chemicals can range from ______seconds to ___________ of years!

24

Iodine-131 has a half-life of 8 days. The decay curve is below:

25

Uses of radiation Dating: Since all radioactive decay occurs at a constant, set rate and we can not speed it up or slow it down, we can use nuclear chemistry to “date” how old something is. Organic Material Carbon-14 14

6C → 147N + 0-1e T½ = _________ Assumptions.

1. The rate has always been the same. 2. The amount of 14C is the same now as it has always been.

Carbon-14 dating works well for about __________ years, after that it can be suspect. Inorganic Material Age of the earth: Determined using 40K → 40Ar + 0+1e T½ = _______________

Medical uses

X-Rays Images hard tissues (bones)

CT scan Uses x-rays and the density of tissues-used to detect brain tumors

MRI Uses the “spin” of H atoms-useful to “see” the inside of the

body Ultrasound Images soft tissues with high water content.

PET scan Uses positron emission of 11C-useful in detecting what parts of the brain are working

Therapy Ionizing radiation damages cells, especially those that divide

rapidly (cancer)

26

Energy Fusion

21H + 31H → 42He + 10n + energy

This is how the ______ makes its energy, hydrogen bombs work, and how scientists make ______ elements

Fission 235

92U + 10n → 14156Ba + 92

36Kr + 3 10n + γ Fission was discovered in the 1930s and is used in nuclear _______________ and the _______________.

27

Notice-the reaction uses 1 neutron but produces ___ neutrons-thus the reaction is self-propagating and often called a __________________

Nuclear Power plant:

28

Practice Problems Fill in the blank for the following reactions

1. 184Ir → 0+1e + _____

2. 125Sn → 0-1e + _____

3. ____ → 0-1e + 40Ca

4. 23Na + _____ → 23Mg + 10n

5. 59Co + 10n → 56Mn + _____

6. 96Mo + 42He → 100Tc + _____

7. 238U + 16O → _____ + 5 10n

8. 147Sm → ____ + 143Nd

9. _____ + 1H → 29Si + γ

10. 40Ar + _____ → 43K + 1H

11. What would be the product if a 205Po isotope underwent alpha emission?

12. What would be the product if a 116In isotope underwent beta emission?

Answ

ers

1. 18

4 76

Os

2. 12

55

1Sb

3.

4019K

4.

1 1H

5.

4 2He

6.

0 +1e

7.

249 10

0Fm

8. 4 2H

e 9.

28

13Al

10

. 4 2H

e 11.

201 82

Pb

12.

1165

0Sn

Unit 4 Practice Test

You will be given any formulas needed on the test.

Use the following reaction for questions 1-4

N2(g) + 3H2(g) 2NH3(g) + Heat 1. If the [N2] = 0.24, [H2] = 0.41, and the

[NH3] = 0.31 calculate the value of K a. 3.2 b. 5.8 c. 0.17 d. None of the above

2. If the pressure is increased the equilibrium

will a. Shift toward products b. Shift toward reactants c. Not shift at all

3. If H2 is added the equilibrium will

a. Shift toward products b. Shift toward reactants c. Not shift at all

4. If the temperature is increased the

equilibrium will a. Shift toward products b. Shift toward reactants c. Not shift at all

5. What is the name of H2CO3

a. Carbonic acid b. Hydrocarbonic acid c. Carbonous acid d. None of the above

6. An Arrhenius Acid is a chemical that a. Produces OH- in water b. Produces H3O+ in water c. Donates a proton d. Accepts a proton

Use the following reaction for questions 7-8

H3O+(aq) + HPO4

2-(aq) → H2PO4

-(aq) + H2O(l)

7. Which chemical is the conjugate acid?

a. H3O+ b. HPO4

2- c. H2PO4

- d. H2O

8. Which chemical is the base

a. H3O+ b. HPO4

2- c. H2PO4

- d. H2O

9. If the pOH of a solution is 6.9 than the [H3O+] is a. 1.3 x 10-7 b. 5.9 x 10-5 c. 7.9 x 10-8 d. None of the above

10. If the pH of a solution is 4.2 then the pOH

is a. 4.2 b. 18.2 c. 9.8 d. None of the above

11. If the [OH-] = 1.87 x 10-4 than the solution is a. Acidic b. Basic c. Neutral d. Can’t be determined without further

information 12. 209Po is an unstable isotope that decays by

emitting alpha radiation. What new isotope would be formed? a. 209At b. 205Pb c. 209Bi d. 209Po

13. Fill in the blank for the following reaction 10n + 235U → 137Te + _______ + 2 10n

a. 98Zr b. 97Zr c. 97Bk d. None of the above

14. The reaction in question 13 is a/an

________ reaction a. Alpha emission b. Beta emission c. Fusion d. Fission

Ans

wer

s:

1. B

2. A

3.

A 4.

B

5.

A 6.

B

7.

C 8.

B 9.

C

10.

C 11.

B 12

. B

13.

B 14

. D