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Steps for Balancing Equations
1.Write the skeleton equation Use arrows, +/- & physical states of matter
2. Count the atoms of the reactants3. Count the atoms of the products
4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation
5. Write the coefficients in their lowest possible ratio
NEVER, NEVER CHANGE THE
SUBSCRIPT
Count the reactants & products
Balance the H & O atoms with coefficients for the reactants to = the
products
A chemical reaction in which 2 or more reactants produce 1 product
General form A + B AB
In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.
Examples
-2Na + Cl2 2NaCL
- 2Mg + O2 2MgO
- 4Al + 3O2 2Al2O3
- H20 + SO3 H2SO4 (this is one cause of acid rain)
- H20 +CO2 H2CO3 (this is why rainwater is naturally acidic)
- H2O + MgO Mg(OH)2
Special CASE “Scenarios” for these RXN’s
Metallic oxide + Water Base Na2O + H2O 2NaOH
Non-Metallic oxide + Water Acid
SO3 + H2O H2SO4
Special CASE “Scenarios” for these RXN’s
Metallic oxide + CO2 Metal carbonate
Metal chloride + Oxygen Metal chlorate
CaO + CO2 CaCO3
2KCl + 3O2 2KClO3
A chemical reaction where 1 compound, breaks apart into 2 or more
simpler productsGeneral form AB A + B
In this cartoon the egg (the reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances.
Examples
- 2 H2O 2H2 + O2
- 2HgO 2Hg + O2
- 2Ag2O 4Ag + O2
- CaCO3 CaO + CO2
- H2CO3 H2O + CO2 -Decomposition reactions often require an
energy source:
Heat
Light
Electricity
Special CASE “Scenarios” for these RXN’s
Heating an acid non metallic oxide + water
Heating a carbonate oxide + CO2
Heating a base metallic oxide + water
Heating a metal chlorate chloride + O2
Heating a metallic oxide Metal + O2
These are just the reverse of their synthesis RXN’s
Heating a sulfite Metal oxide + SO2
A reaction in which atoms of one element replace the atoms of another element that
is part of a compound
Notice, the guy in the orange shirt steals the date of the other guy. So, a part of one of the reactants trades places and is in a different
place among the products
2. Anions replace Anions
1. Cations replace Cations
General Form AB + C CB + A
C would be the cation/metal and so replaced A, which would have to be a cation
General Form DE + F DF + E
F would be the anion/non-metal and so replaced E, which would have to be a anion
Examples:
a.Cu + AgNO3 Cu(NO3)2 + Ag
Cation replaces Cation
b.NaI + Cl2 NaCl + I2
Anion replaces Anion
Special situations for SR RXN’s1. Activity Series
Definition
A list of metal/cations in order of decreasing reactivity
Used to determine if one metal can replace another in a RXN
The higher its position on chart the more metals it can replaceEx: sodium will replace aluminum
The lower its position on the chart the less metals it can replaceEx: zinc will not replace magnesium
3. Halogens The halogens also have a series;
As you go down group 17 they decrease in reactivityEx: Chlorine cannot replace fluorine but it can replace bromine
Special situations for SR RXN’s2. Water for writing RXN’s it may be useful to write water
as H(OH). Why?
Special situations for SR RXN’s
Do the following reactions occur? Explain.
Zn + H2SO4 H2 + ZnSO4
Sn + 2NaNO3 Sn(NO3)2 + 2Na
2NaCl + F2 2NaF + Cl2
CaCl2 + I2 CaI2 + Cl2
A reaction where there is an exchange of cations between 2 ionic compounds
Notice how the first guy exchanged hats with the second guy, so they are
both wearing each other's hat.
General FormAB + CD AD + CB
** Make sure of cation and anion placement
Ex: BaCl2 + K2CO3 BaCO3 + 2KCl
3KOH + H3PO4 3H(OH) + K3PO4
“Driving Forces” in double replacement RXN’s
One of three things must form for these RXN’s to occur
1. A molecular compound like water forms
2. A gas forms that bubbles out i.e. (H2, CO2, H2S, CO, etc.)
3. A precipitate forms
“Driving Forces” allow a RXN to take placeUse your net ionic equation to see if one of the following are formed
How do you know if something is a precipitate?
1. It is insoluble or slightly soluble in water 2. Check your solubility chart
Examples: will these RXN’s occur? Explain
BaCl2AgCl
Ca3(PO4)2
NaNO3
Soluble….NR
Insoluble….YesInsoluble….Yes
Soluble….NR
Examples: will these RXN’s occur?
FeS(s) + HCl(aq) FeCl2(aq) + H2S ↑
Pb(NO3)2 (aq) + 2KI (aq) 2KNO3 (aq) + PbI2 ↓
FeCl3 (aq) + Al(NO3)3 (aq) Fe(NO3)3 (aq) + AlCl3 (aq)
Yes
Yes
No…soluble …no “driving force” present
Definition:Oxygen reacts with another substance often producing energy in the form of heat and light
Types:
1. Complete combustion
Hydrocarbons combine with oxygen to produce carbon dioxide and water
Definition:
If sufficient oxygen is present to burn completely
General form: CxHy + O2 CO2 + H2O
Definition:
2. Incomplete combustion
Insufficient oxygen is present to burn completely
Hydrocarbons combine with oxygen to produce poisonous carbon monoxide and solid elemental carbon as well as carbon dioxide and water
Examples:
Extra “Special” RXN’s
• Reactive metals and water (SR)
• Group 1 and 2 metals react to form a metal hydroxide and hydrogen gas
• Acid and a Base
• React to form a salt (ionic compound composed of the anion of the acid and the cation of the base) and water
Aqueous SLN
• When two (aq) solutions that contain ions as solutes combine….
• The ions may react with one another
• The H20 molecules don’t usually react
• The three types of products can form aka “driving forces” …. Gas, water, or precip
• Chemical equations do not always show all that happens in a RXN
• Solutions are composed of
• Solute
• Solvent
• Aqueous SLN
• Is a sln in which the solvent is water
Net Ionic Equations
Net Ionic Equations
• Substances that are ions in a solution and are written as such
• These equations show all of the particles in a solution as they “really” exist
• Some ions are in both the RXT & PROD, these are called…
• SPECTATOR IONS
Net Ionic Equations
• SPECTATOR IONS - dissociation only occurs if it is in an aqueous solution
• S, L, G are not ions see your solubility chart
Net Ionic Equations
• Regular equation• 2NaOH (aq) + CuCl2 (aq) 2NaCl (aq) + Cu(OH)2(s)
• Ionic equation• 2Na+ (aq) + 2OH- (aq) + Cu+2(aq) + 2Cl- (aq) 2Na+
(aq) + 2Cl- (aq) + Cu(OH)2 (s)
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