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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
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
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?
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?
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
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
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 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.