If we’re going to do chemical reactions with antacids, we’d better know how to write them!

Unit 2B

Section 2.6

Watch as 2 H2 and 1 O2 undergo a chemical reaction

OO OO

Bonds are broken and atoms are rearranged to form new compounds.

HH

HH HH HH

2 H2 + O2 2 H2O

What is a Chemical Reaction?

OO OO

Bonds and atoms are rearranged to form new compounds.

HH HH

OOHH

HHOOHH

HH HH HHThe compounds in the end are different from those in the beginning

Bonds are broken and formed between different atoms

2 H2 + O2 2 H2O

Chemical Reactions

• When bonds of substances are broken and atoms rearrange to form new substances

• Also known as a chemical change

2 H2 + O2 2 H2O

What is a Chemical Reaction?

Observations (Indicators) of a Chemical Reaction(change)

•Color change

•Odor change

•Gas production

•Precipitate formation: insoluble solid that is formed when 2 aqueous solutions are reacted•Temperature change

•Exothermic Reactions: reactants release heat & temp. of reaction increases•Endothermic Reactions: reactants absorb heat energy & temp. of reaction decreases

What are Chemical Equations?

NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)

Reactants

Physical State Arrow

ProductsWhat you start with

s = solid l = liquidg = gas aq = aqueous (dissolved in water)

: Read as: Yields, Produces, Forms

What you end with

• The “sentence” of chemistry • Uses chemical formulas & other symbols instead of

words to show a chemical reaction

Examples of Chemical Equations

H Cl

HMg H

H Cl

Mg ClCl

H Cl

HMg H

H Cl

Mg ClCl

Word equation: Magnesium metal is reacted with aqueous hydrochloric

acid to produce aqueous magnesium chloride and hydrogen gas 

Visualization

Formula equation: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)

You must write the correct chemical formula for each reactant & product (Section 2.2)

“and”, “is mixed with” or “reacts with” = +“yield”, “produces” and “forms” = Remember “BrINClHOF”: to represent the

7 diatomic elements that have a subscript of 2 in their chemical formula

Br2 I2 N2 Cl2 H2 O2 F2

Writing Chemical Equations

Let’s Practice #1

Example:Write the word equation into symbol form

Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas

Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas

Let’s Practice #1

Al + HCl AlCl3 + H2

Example:Write the word equation into symbol form

Let’s Practice #2

Example:Write the word equation into symbol form

Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate

Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate

Let’s Practice #2

Cu(NO3)2 + NaOH Cu(OH)2 + NaNO3

Example:Write the word equation into symbol form

Synthesis(Combination): when 2 or more substances combine to form a SINGLE substance

Element + Element Compound Cu + S CuS

Compound + Compound Compound Li2O + H2O LiOH

Decomposition: when 1 substance breaks apart into 2 or more substances; requires Energy to initiate

Compound Element + Element CaS Ca + S

Compound Compound + Compound H2O2 H2O + O2

Single Replacement: when a more reactive element replaces a less reactive element in a compound

Compound + Element Element + Compound AgI + K Ag + KI

Double Replacement:when the positive ions of each aqueous compound replace each other

Compound + Compound Compound + Compound

KI + AgNO3 AgI + KNO3

+ +

Combustion:reaction of an element or compound with OXYGEN to form an oxide & produce heathydrocarbons combust to always produce carbon dioxide,water & heat

Mg + O2 MgO

CH4 + O2 CO2 + H2O

Section 2.7—Balancing Equations

We need to finish writing those equations we started!

Law of Conservation of Mass

Matter cannot be created nor destroyed just changed in form. Thus mass must remain constant through changes.

Conservation of Mass

CaCl2 + Na2SO4 CaSO4 + 2NaCl

Mass before(reactants) = mass after(products)

# atoms before (reactants) = # atoms after(products)

How Does the Law Lead to Balancing?

.

Matter cannot be created nor destroyed during a chemical or physical change.

The number of atoms of each element must be the same on both sides To ensure this we must balance the equation

How Do We Begin?Start by Counting the Atoms of each Substance

Subscripts tell you how many atomsCoefficients are always multiplied by subscriptsWith a parentheses, inner & outer subscripts are

always multiplied together

Try These!

Count the atoms in each compound

(a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___

(b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___

How Do We Balance Equations?

Practice Problems: How many atoms of each type are indicated in the following compounds?

(a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___

(b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___

(c) 3 Ca(NO3)2 Ca= ___ N= ___ O= ___

6

4

3

24

8

6

2 8

12 8

18

Coefficients are added to change the number of atoms in a substance!

CH4 + 2 O2 CO2 + 2 H2O

Total:1 C4 H4 O

Total:1 C4 H4 O

The equation is balanced.

H

C

H

HH

O O

O O

CO O HO

H

HO

H

H

CC

H

HH

O O

O O

CCO O HO

H

HO

H

Make a table of elements

_____ __________

How to Balance Chemical Equations:

1

Reactants Products

H

O

C

CH4 + O2 H2 O CO2+_____

2 Count the number of each element or ion on the reactants and products side.

_____ __________

How to Balance By Inspection:

Reactants Products

H

O

4

2 3

2

C 1 1

CH4 + O2 H2 O CO2+_____

Don’t forget to add all the atoms of the same element together—even if it appears in more than one compound!

3Each time you add a coefficient, update your table with the new quantities of each atom.

Use coefficients to balance the numbers

_____ __________2

How to Balance By Inspection:

Reactants Products

H

O

4

2 3

2

C 1 1

2

4

44

CH4 + O2 _____ H2 O CO2+

4

Filling each coefficient location lets you and the grader know that you finished the problem rather than you left some blank because you weren’t done!

OPTIONALPlace a “1” in any empty coefficient location

_____ __________2

How to Balance By Inspection:

Reactants Products

H

O

4

2 3

2

C 1 1

2

4

44

1 1CH4 + O2 _____ H2 O CO2+

Choosing the Order of Balancing

Save for laterElements that are uncombined

StartElements that appear

only 1 time per side

StartElements in most

complicated molecules

How do you know what order to balance in?

Pb + PbO2 + H+ Pb2+ + H2O

To balance this equation, use the order: O, H, Pb

_____

How is Balancing Affected by Order?

What happens if we balance in the order determined in the last slide?

Reactants Products

H

Pb

1

2 1

2

O 2 1

4

2

_____ __________1 21 2Pb Pb+ O2 H2 O Pb2++H+_____4+

2

4

O, H, Pb

2

_____

What about a different order?

How is it different if we balance in a different order?

Reactants Products

O

Pb

2

2 1

1

H 1

2

2

_____ __________1 21 2Pb Pb+ O2 H2 O Pb2++H+_____2+

2 4

4

4

You’ll still get to the correct answer, but it will take longer and be more complicated!

H, O, Pb

Do You Remember Polyatomic Ions?

Polyatomic ion – Group of atoms that together has a net charge

e.g. Nitrate NO31-

Carbonate CO32-

OH is a polyatomic ion that is sometimes “hidden” in H2O.

Re-write H2O as HOH to “see” the OH polyatomic ion.

Make a table of elements

Hint: Chunk the polyatomic ions—IF they appear on both sides

__________ __________

Balancing with Polyatomic Ions:

Reactants Products

PO4

Ca

H

Ca (OH)2+H3 Ca3 (PO4)2 H2O+PO4

OH

HOH

1

2 Count the number of each element or ion on the reactants and products side.

__________ __________

Balancing with Polyatomic Ions:

Reactants Products

PO4

Ca

1

1 3

2

H 3 1

Ca (OH)2+H3 Ca3 (PO4)2 H2O+PO4

OH 2 1

HOH

3 Add coefficients to balance the numbers

__________ __________2

Balancing with Polyatomic Ions:

Reactants Products

PO4

Ca

1

1 3

2

H 3 1 6

3

3 6Ca (OH)2+H3 Ca3 (PO4)2 H2O+PO4

OH 2 1

HOH

6

2

6 6

5 Place a “1” in any empty coefficient location

__________ __________2

Balancing with Polyatomic Ions:

Reactants Products

PO4

Ca

1

1 3

2

H 3 1

1

6

3

3 6Ca (OH)2+H3 Ca3 (PO4)2 H2O+PO4

OH 2 1

HOH

6

2

6 6

Let’s Practice #1 Example:Balance the

following equation

__ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O

Example:Balance the

following equation

__ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O2 1 1 2

HOH

Did you see the “OH” polyatomic ion & change H2O to HOH?

Let’s Practice #2 Example:Balance the

following equation

__ H2 + __ O2 __ H2O

Example:Balance the

following equation

__ H2 + __ O2 __ H2O2 1 2

Let’s Practice #3 Example:Balance the

following equation

__ Fe + __ O2 ___ Fe2O3

Example:Balance the

following equation

__ Fe + __ O2 ___ Fe2O34 3 2

Practice Problems1. 2 5 4 2

combustion 2. 1 1 1 1 SR

3. 1 2 2 1 SR 4. 2 2 1 decomp 5. 1 1 1 synthesis

6. 16 1 8 synthesis 7. 1 1 1 2 DR

8. 4 3 4 3 SR

Continuation of Answers

9. 1 2 1 2 DR10. 3 1 1 synthesis11. 4 1 2 synthesis12. 1 3 1 decomp13. 1 2 1 1 SR14. 2 3 2 3 DR15. 1 1 1 2 DR

Predicting Products of a Chemical Reaction

Section 2.8To be successful in this section, you will

need to use the reaction models

found on the Reference Sheet

Steps to Predicting Products of a Chemical Reaction1. Identify the type of reaction.

2. Use the reference sheet to determine which model to use.

3. Create products for your reaction following the model as a guide.

4. As you form new ionic compounds, don’t forget to check charges.

5. Make sure to recognize the elements of BrINClHOF & format them correctly.

6. Balance the chemical equation.

Synthesis Reaction: Model 1AFormation of a Binary Ionic Compound

A + B ABmetal + nonmetal binary ionic compound

What do you do?Bring symbols together and check charges

Example:

K + Br2

Synthesis Reaction: Model 1BMetal oxide & water forms a base

MO + H2O MOHMetal oxide + water metal hydroxide

What do you do?Combine metal symbol with hydroxide (OH) & check charges

Example:

CaO + H2O

Synthesis Reaction: Model 1CNonmetal oxide & water forms an acid

NMO + H2O Hx(NM)Oy

Nonmetal oxide + water oxyacid

What do you do?Add up all atoms starting with H, then the nonmetal, ending with O.

Example:

CO2 + H2O

Decomposition Reaction: Model 2ABreak down of a Binary Compound

AB A + BBinary compound element + element

What do you do?Break binary compound apart into the 2 elements that make it upLook for diatomic elements!

Example:

CaCl2

Decomposition Reaction: Model 2BMetal Carbonates

MCO3 MO + CO2

Metal carbonate metal oxide + carbon dioxide gas

What do you do?Place metal next to oxygen & check charges Then add carbon dioxide, CO2

Example:

K2CO3

Decomposition Reaction: Model 2CMetal Hydrogen Carbonates

(bicarbonates) MHCO3 MO + H2O + CO2Metal hydrogen carbonate metal oxide + water + carbon dioxide

What do you do?Place metal next to oxygen & check charges Then add water, H2O & then carbon dioxide, CO2

Example:

NaHCO3

Decomposition Reaction: Model 2DMetal Hydroxides

MOH MO + H2O Metal hydroxide metal oxide + water

What do you do?Place metal next to oxygen & check charges Then add water, H2O

Example:

LiOH

Decomposition Reaction: Model 2EMetal Chlorates

MClO3 MCl + O2 Metal chlorate metal chloride + oxygen gas

What do you do?Place metal next to chlorine & check charges Then add oxygen gas, O2

Example:

AgClO3

Decomposition Reaction: Model 2FOxyAcids

Hx(NM)Oy NMO + H2O oxyacid nonmetal oxide + water

What do you do?Remove water (H2O) from the oxyacid to form the nonmetal oxide

Example:

H2SO3

Using the Activity Series: The Activity Series is a chart that shows the reactivity of metals

found on your reference sheet

Elements on top of the chart are more reactive than elements on the bottom

More reactive elements can only replace less reactive elements within a compound

Self Check

Using the activity series, determine if the following replacements can happen:

1.K + CaCl2

2.Cu + Zn(OH)2

3.Na + H2O

4.Ni + H2O

5.Mg + HCl

Single Replacement Reaction: Model 3AMore Reactive Metal replacing Less Reactive Metal

A + BC AC + B metal + ionic compound new ionic compound + new metal

What do you do?Check Activity Series: Is the single metal

above the metal in the compound?If YES, replace it & check charges of new

compound. Be on alert for diatomic elements!If NO, write NR for “no reaction”.

Example:

Zn + Cu(NO3)2

Single Replacement Reaction: Model 3BMore Reactive Metal replacing Hydrogen from Water

M + H2O MOH + H2 metal + water metal hydroxide + hydrogen gas

What do you do?Change H2O to HOH.

Check Activity Series: Is the single metal above the Hydrogen? Look at the specific details about temperature of water.If YES, replace it & check charges of new compound. Then add hydrogen gas, H2.

If NO, write NR for “no reaction”.

Single Replacement Reaction: Model 3BMore Reactive Metal replacing Hydrogen from Water

M + H2O MOH + H2 metal + water metal hydroxide + hydrogen gas

Examples:

Na + H2O

Al + H2O

Single Replacement Reaction: Model 3CMore Reactive Metal replacing Hydrogen from an Acid

M + HX MX + H2 metal + acid ionic compound + hydrogen gas

What do you do?Check Activity Series: Is the single

metal above the Hydrogen? If YES, replace it & check charges

of new compound. Then add

hydrogen gas, H2.

If NO, write NR for “no reaction”.

Example:

Mg + HCl

Single Replacement Reaction: Model 3DMore Reactive Halogen replacing Less Reactive Halogen

D + BC BD + C Element + ionic compound ionic compound + element

(halogen) (halogen)

What do you do?Check Activity Series: Is the single

halogen above the halogen in the chart? If YES, replace it & check charges

of new compound. Be on alert for diatomic

elements!If NO, write NR for “no reaction”.

Examples:

Cl2 + KBr

I2 + NaCl

Solubility Rules Chart: The Solubility Rules Chart classifies substances as soluble or insoluble

found on your reference sheet Categorized by Anion SOLUBLE- means that the substance will dissolve in water

INSOLUBLE- means that the substance will not dissolve in water and so it is considered a PRECIPITATE

Self CheckUsing the Solubility Rules, determine if the

following substances are soluble or insoluble(precipitate):

1. CaCl2 4. Zn(OH)2

2. K3PO4 5. NiSO4

3. MgCO3 6. AgNO3

Double Replacement Reaction: Model 4AFormation of a Precipitate

AB + CD AD + CB Aq. compound + Aq. Compound compound + compound

(1 of the products is a precipitate)

What do you do?Swap the positive ions with each other & check the charges on the new compoundsUsing the Solubility Rules chart, identify the product that is a precipitate (INSOLUBLE)

Example: NaCl + AgNO3

Double Replacement Reaction: Model 4BAcid Base Reaction

AB + CD AD + CB Acid or Base + Acid or Base ionic compound + water

(salt)

What do you do?Identify the reactants as an acid & base. No need to use solubility rules chart!Swap the positive ions with each other & check the charges on the new compounds which will always be a salt & water.

Example:

KOH + H2SO4

CombustionReaction: Model 5

CxHy + O2 CO2 + H2O Hydrocarbon + oxygen carbon dioxide + water

What do you do?Identify the hydrocarbon and O2 as reactants

Products will always be CO2 and H2O no matter what the formula of the hydrocarbon

Examples:

C3H8 + O2

CH3OH + O2

Section 2.8—Speeding Up A Reaction

Section 2.9

How can we make those antacid reactions occur faster?

Reaction Rate tEd Video Clip

http://ed.ted.com/lessons/how-to-speed-up-chemical-reactions-and-get-a-date

Reaction Rate – the change in amount of reactant or product per change in time

Kinetics – Study of the how fast (rate) a reaction occurs

Kinetics & Reaction Rates

Collision Theory – In order to react, molecules must have effective collisions:

Reactants must collide

Collision must be at the correct orientation

Collision must meet a minimum energy for reaction to occur which is called Activation Energy

1

2

3

There must be an increase in effective collisions in order to increase reaction rate! Only a small number of collisions meet the requirements and result in a reaction.

How does this relate to reaction rates?

Collision Theory Visual

Collisions Must Occur

In order for two molecules to react, they must come in contact with one another

FF

FFNN

OO

OO

There’s no way they’ll ever react if they don’t run into one another!

Collision with Correct Orientation

For a collision to result in a chemical reaction, it must occur with the correct orientation

FF

FFNN

OO

OO

This is not the correct orientation. The reaction will not happen.

NNOO

OO

FF

FF

Collision with Correct Orientation

For a collision to result in a chemical reaction, it must occur with the correct orientation

FF FF

NNOO

OO

This is the correct orientation. The reaction will happen.

FF

FF

Collision with Enough Energy

For a collision to result in a chemical reaction, it must meet the minimum energy (called activation energy) for reaction to occur.

NNOO

OO

The collision does not have enough energy to produce a reaction

FF

FF

This collision had more energy (faster moving molecules). A reaction will occur..

NNOO

OO

Collision with Enough Energy

For a collision to result in a chemical reaction, it must occur with the minimum energy for reactionCalled Activation Energy

FF FF

NNOO

OO

Reaction Coordinate Diagram

Products

Activated complex(Also called the transition state)

Activation Energy

ReactantsEnergy change for reaction

Reaction coordinate diagrams show the energy changes throughout the reaction

Reaction proceeds

Ene

rgy

F + FNO2

FF

FF

Activated ComplexWhat is an “activated complex”?A temporary molecule formed during a reaction

Reaction proceeds

Ene

rgy

NNOO

OOFF FF

NNOO

OO

ReactantsActivated Complex

Products

F2 + NO2

F2NO2

Factors Affecting Reaction Rates

1. Nature of Reactant: Some substances are just more reactive than others.

2. Surface Area of Reactants

How does the surface area of the reactants affect the reaction rate?

More surface means more reactant particles can come in contact with each other at the same time

As surface area increases, more effective collisions!

Reaction Rate Increases!

Effect of surface area on rate of reaction Any reaction involving a solid can only take place at

the surface of the solid.

If the solid is split into several pieces, the surface area increases. What effect will this have on rate of reaction?

The smaller the pieces, the larger the surface area. This means more collisions and a greater chance of reaction.

This means that there is an increased area for the reactant particles to collide with.

low surface area high surface area

Surface Area Simulationhttp://courses.soil.ncsu.edu/resources/phy

sics/texture/soilgeo.swf

Surface area and particle collisions

3. Concentrations of Reactants

How does the concentration of reactants affect the reaction rate?

More reactants mean more effective collisions will occur As reaction concentration increases, reaction

rate increases!

1M HCl is not as concentrated as 3M HCl

Concentration and particle collisions

The effect of concentration on rate

4. Temperature

How does temperature affect the reaction rate?Reactants must collide with at least an energy equal to the activation energy

Molecules at a higher temperature, have higher average kinetic energy, so they move faster and collide more often

Effect of Temperature on Rate

For most reactions, as temperature increases, reaction rate increases. Not only does It increase collision frequency & effectiveness of collision. But a higher KE, means its easier to attain the Ea of the reactionA rise in temperature of just 10 °C can double the rate of a reaction

.

Temperature and particle collisions

The effect of temperature on rate

Temperature and batteries

Why are batteries more likely to rundown more quickly in cold weather?

At low temperatures the reaction that generates the electric current proceeds more slowly than at higher temperatures.

This means batteries are less likely to deliver enough current to meet demand.

5. Catalysts

Catalyst – A substance that increases the rate of reaction without being used up

A + B + C D + C

“C” is the catalyst…it is present in the beginning and in the end

Enzymes are catalysts in the body

Catalysts change the pathway of a reaction

Reaction Path without catalyst

Reaction Path with catalyst

Reaction proceeds

Ene

rgy

Catalysts lower the activation energy of the reaction by letting it proceed in a different way. LOWER Ea = faster reaction

Everyday catalysts

Nickel is a catalyst in the production of margarine (hydrogenation of vegetable oils).

Many catalysts are transition metals or their compounds. For example:

Platinum is a catalyst in the catalytic converters of car exhausts. It catalyzes the conversion of carbon monoxide and nitrogen oxide into the less polluting carbon dioxide and nitrogen.

Iron is a catalyst in the production of ammonia from nitrogen and hydrogen (the Haber process).

Catalysts in industry

Catalysts are also essential for living cells. Biological catalysts are special types of protein called enzymes.

Why are catalysts so important for industry?

Products can be made more quickly, saving time and money.

Catalysts reduce the need for high temperatures, saving fuel and reducing pollution.