1. Recognize Evidence of a chemical change. 2. Represent chemical reactions with equations. 3....
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Transcript of 1. Recognize Evidence of a chemical change. 2. Represent chemical reactions with equations. 3....
Ch
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ical R
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Objectives
1. Recognize Evidence of a chemical change.2. Represent chemical reactions with equations.3. Change word equations into formula equations.4. Given a description of a reaction, write a word and
formula equation.5. Balance chemical equations.6. Translate a formula equation into a sentence.7. Define and give a description of the major types of
chemical reactions.8. Classify reactions as one of five major types.9. Predict the products of simple reactions when given the
reactants.10. Understand, explain, and apply the activity series of the
elements.
Skills
1. Memorize the diatomic elements2. Memorize the symbols used in chemical equations. 3. Use the Activity Series for single replacement
reactions 4. Use the Solubility Chart for Double Replacement
Reactions5. Know common gases 6. Memorize substances that decompose
Carbonic acid, H2CO3 H2CO3 (aq) H2O+ CO2(g)
Sulfurous acid, H2SO3 H2SO3 (aq) H2O + SO2(g)
Ammonium hydroxide, NH4OH NH4OH (aq) H2O + NH3(g)
Chemical Reaction
The process by which one or more substances are rearranged to form different substances is called a chemical reaction.Also called a chemical change
Activity 1: Name Some Common Chemical Reactions
Equations show
o the reactants which enter into a reaction.
o the products which are formed by the reaction.
o the relative amounts of each substance used and each substance produced.
o Reactants ® Products
Two important principles to remember
Every chemical compound has a formula which cannot be altered.
A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.
Evidence of a Chemical ReactionActivity #2 Indicators of a chemical reaction
Procedure1. Add 10.0 mL od distilled water to a small beaker. 2. Add 1 drop of .1 M NaOH to the water. 3. Add 15 drops of universal indicator to the water. Stir. 4. Record the color of the water. 5. Record the temperature of the water. 6. Drop an alka seltzer tablet into the water. 7. Observe the reaction. Record all observations including any temperature
change. Analysis Questions
Describe any color changes or temperature changes. Was a gas produced? How do you know? Did chemical change occur? Explain how you know. What is the purpose of the universal indicator? Make a list of five indicators of a chemical reaction.
Evidence of a Chemical Reaction
Production of a Gas Temperature Change Color Change Production of a Solid (precipitate) Production of Water or other unionized
substance
Representing Reactions
We use chemical equations to represent reactions
Ways to show equationsSentence DescriptionsWord EquationsSkeleton Equations Balanced Chemical Equation
Sentence Descriptions
Every item is a word. Copper reacts with chlorine to form copper (II)
chloride
Iron (III) chloride is produced from iron metal reacting with chlorine gas
Word Equations
Words and symbols are used. Copper + chlorine ® copper (II) chloride
iron(s) + chlorine(g) iron(III) chloride(s)
Skeleton Equation
Uses chemical formulas instead of words
Fe (s) + Cl2 (g) FeCl3 (s)
Balanced Chemical Equation
2Fe (s) + 3Cl2 (g) 2FeCl3 (s)
Some things to remember about writing equations
The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2
The sign, → , means "yields" and shows the direction of the action.
A small delta, ( ), above the arrow shows that heat has been added.
A double arrow, ↔ , shows that the reaction is reversible and can go in both directions.
Chemical Equation
In order to obey the Law of Conservation of Mass equations must be Balanced:
Coefficients: number written in front of
a chemical formula to indicate the smallest number of particles involved in the reaction.
Steps for Balancing
Write skeleton equation. Change the coefficients to make the
number of atoms of each element equal on both sides of the equation. NEVER CHANGE A SUBSCRIPT!!!
Write the coefficients in the smallest ratio possible.
Check your work.
Helpful hints for balancing chemical equations
Start with “Big Formulas” C2H6O2
Save single elements for last O2 or Cu Balance hydrogens second to last Balance oxygens last Check for lowest ratio Do not change your subscripts Balance the polyatomic ions as one unit
(if it didn’t break apart) Perform a final check
If your equation doesn’t balance,
check your formulas!!
Classifying Chemical Reactions
Five Types of Chemical
ReactionsSynthesis ReactionDecomposition ReactionSingle Replacement ReactionDouble replacement ReactionCombustion Reaction: oxygen
combines with a substance and produces heat and light
Synthesis Reaction: one product is formed from more than one simpler substances
A + B AB
Activity: Reaction of Iron with Oxygen Gas
Decomposition Reaction: One substance is broken down into one or more simpler substances: usually by the addition of energy
AB A + B
Activity: Elephant Toothpaste
Decomposition of Hydrogen Peroxide
Single Replacement Reaction: atoms of one element replace another element in a compound
A + BC B + AC
Activity: Reaction of iron with copper (II) nitrate
Reaction Notes
Double Replacement Reaction
Involves the exchange of ions between two compounds
AB + CD AD + CBActivity: Copper (II) chloride reacts with sodium hydroxide
Reaction Notes
Oxygen combines with a substance and produces heat and lightMost likely: Hydrocarbon (CxHy) Combustion
CxHy + O2 H2O + CO2
X + O2 X2O3
Demo: Methane Snake
Combustion Reaction
Reaction Notes
Classify Each Reaction
Ca + O2 CaO Br + LiI LiBr + I Al + Fe(NO3)2 Al(NO3)3 + Fe MgO + HCl MgCl2 + H2O C4H10 + O2 CO2 + H2O NH4NO2 NH3 + H2O (NH4)3PO4 + Sr(OH)2 Sr3(PO4)2 + NH4OH H2SO4 + NaOH Na2SO4 + H2O Zn + AgNO3 Zn(NO3)2 + Ag CuNO3 + KCl KNO3 + CuCl
Predicting Products
Given the reactants predict what is formed Write formulas for reactants Identify the type of reaction Rearrange the atoms to write
formulas for products.
Single Replacement Reactions
Atoms of one element replace another element in a compound
A + BC B + AC
There are 3 Ways that a Single Replacement Reaction can occur.
1.) Metal replaces another metal in a compound
when zinc combines with iron (II) chloride the zinc replaces iron in the compound Z n + FeCl2 Fe + ZnCl2
2.) Metal replaces hydrogen in an acid or
water
3.) Nonmetal (halogen) replaces another nonmetal
(halogen)in a compound
Br2 + LiI LiBr + I2
Single Replacement Cartoon
How can we tell if a single replacement reaction will
happen? Use the activity series of the
elements If the free element is more active than
the element in the compound the reaction will happen
If the free element is below the element in the compound the reaction will not happen
The Activity Series
Another way to look at it
Bigger, stronger, orange shirted guy replaces white shirt guy in the dancing couple
Now we have new couple and new single guy
SINGLE REPLACEMENT LAB AND EXAMPLES FOR YOU TO PREDICT
THE PRODUCTS
http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/series/3perform.htm
Some Examples to Observe before lab
Double Replacement Reactions
two ionic compounds are mixed together in water
In water the ionic compounds split into anions and cations.
The cations have an opportunity to swap anions
A reaction occurs, if by swapping anions, a product is formed that cannot split apart into anions and cations
AB + CD AD + CB
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Double Replacement: Will it occur?
A reaction occurs when a pair of ions comes together to produce a substance that removes ions from the solution. one of the following must occur
a precipitate: a solid produced during a reaction
a gas Water or other unionized substance a product that decomposes
http://www.wisc-online.com/objects/ViewObject.aspx?ID=gch1404
No Driving Force What happens when one of the three
possible products is not formed? Nothing All ions remain in solution (dissolved)
NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)
Without a driving force there is no change in the solution so we say No Reaction has taken place
Reactions that form a Precipitate
PbCl2(aq) + KI(aq) PbI2(s)+ KCl(aq)
Solubility Chart
Reactions that form a Gas
Some double replacement reactions produce a gas. We observe this as bubbles or odors given off.
Example: Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) +
H2S(g)
Products that Decompose
Some metathesis reactions do not give the product expected.
the expected product (H2CO3) decomposes to give a gaseous product (CO2) CaCO3 (s) + HCl (aq) CaCl2 (aq) + H2CO3
CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
Products that DecomposeH2SO3 H2O + SO2
H2CO3 H2O + CO2
NH4OH H2O + NH3
Reactions that form Water
These water molecules increase the number of solvent molecules and we see no observable evidence
Usually accompanied by temperature change or
Neutralization which can be seen with an acid base indicator Example: H2SO4 + NaOH Na2SO4 +
H2O
Neutralization Reactions
Generally, when solutions of an acid and a base are combined, the products are a salt and water
HC2H3O2 (aq) + NaOH (aq) NaC2H3O2 (aq) + H2O (l)
Acid + Base Salt + Water
Molecular Equation
The molecular equation lists the reactants and products in their molecular form.
AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3
(aq)
Ionic Equation
In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.
This more accurately reflects the species that are found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
Net Ionic Equation
To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)
AgCl (s) + K+(aq) + NO3-(aq)
Net Ionic Equation
The only things left in the equation are those things that change (i.e., react) during the course of the reaction.
Ag+(aq) + Cl-(aq) AgCl (s)
Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)
AgCl (s) + K+(aq) + NO3-(aq)
Writing Net Ionic Equations
Write a balanced molecular equation. Dissociate all strong electrolytes (strong
acids, strong bases, and soluble ionic salts)
Cross out anything that remains unchanged from the left side to the right side of the equation.
Write the net ionic equation with the species that remain.
Combustion of Hydrocarbons
Hydrocarbon + oxygen CO2 + H2O Hydrocarbon: A compound of
hydrogen and carbon The phrase "To burn" means to
add oxygen unless told otherwise.
Complete Combustion: Hydrocarbon + oxygen CO2 + H2O Complete combustion means the
higher oxidation number is attained.
Incomplete Combustion: Hydrocarbon + oxygen CO + H2O Incomplete combustion means the
lower oxidation number is attained.
Combustion of Hydrocarbons
If oxygen is sufficient, the products are carbon dioxide and water vapor.
If oxygen is low, carbon monoxide will be produced.
automobile engine inside a closed garage or charcoal grill indoors.
Hydrocarbon (CxHy) + O2(g) → CO2(g) + H2O(g) EX. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) EX. 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
Combustion of Propane
C3H8 + O2 --> CO2 + H2O
propane 3 carbons = 3 carbon dioxide molecules
8 hydrogen atoms = four H2O molecules. balance the oxygen
Combustion of Acetylene
• This combustion of acetylene reaction is exothermic, and enough energy is released to melt metal. Used in welding.
Why So Hot??
Triple bond-multiple bonds-short bond length
Combustion Of Methane
Demo: Methane Snake Reaction CH4 + 2O2 CO2 + 2H2O
Synthesis Reactions
A + B AB Elem/Cmpd + Elem/Cmpd Compound One Product
Examples of Synthesis Reactions
Metal + oxygen → metal oxide 2Mg(s) + O2(g) → 2MgO(s)
Nonmetal + oxygen → nonmetallic oxide C(s) + O2(g) → CO2(g)
Metal oxide + water → metallic hydroxide MgO(s) + H2O(l) → Mg(OH)2(s)
Nonmetallic oxide + water → acid CO2(g) + H2O(l) → ; H2CO3(aq)
Metal + nonmetal → salt 2 Na(s) + Cl2(g) → 2NaCl(s)
A few nonmetals combine with each other 2P(s) + 3Cl2(g) → 2PCl3(g)
These two reactions must be remembered: N2(g) + 3H2(g) → 2NH3(g) NH3(g) + H2O(l) → NH4OH(aq)
Decomposition Reactions
AB A + B Compound Cmpd/Elem + Elem/Cmpd One Reactant
Examples of Decomposition Reactions AX → A + X
Metallic carbonates, when heated, form metallic oxides and CO2(g)
CaCO3(s) → CaO(s) + CO2(g)
Most metallic hydroxides, when heated, decompose into metallic oxides and water Ca(OH)2(s) → CaO(s) + H2O(g)
Metallic chlorates, when heated, decompose into metallic chlorides and oxygen 2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic oxides and water H2SO4 → H2O(l) + SO3(g)
Some oxides, when heated, decompose 2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity 2H2O(l) → 2H2(g) + O2(g) 2NaCl(l) → 2Na(s) + Cl2(g)
Summary
A + B AB (synthesis)AB A + B (decomposition)A + BC B + AC(single replacement)AB + CD AC + BD(double replacement)Hydrocarbon + oxygen CO2 + H2O(combustion/oxidation)