lesson 9 chemical reactions anything in black letters = write it in your notes (‘knowts’)
TRANSCRIPT
Lesson 9Lesson 9
Chemical ReactionsChemical Reactions
Anything in black letters = write it in your notes (‘knowts’)
Quick Review…Quick Review…
2
Write the chemical formula for sodium carbonate
CO3-2Na+1
sodium ion carbonate ion
Na CO3
Section 1 – Counting AtomsSection 1 – Counting Atoms
Subscripts
2
Coefficient
Na2CO3
Subscripts represent the number of atoms in a compound.
Compound Number and type of atom in compound
Ca Cl Na C O
CaCl2
Na2CO3
NaCl
CaCO3
Coefficients represent the number of each element or compound
Compound Number and type of atom in compound
Ca Cl Na C O
3CaCl2
2Na2CO3
2NaCl
4CaCO3
Chemical equations represent chemical reactions
Reactants Products
Reactant mass = Product mass
# reactant atoms = # product atoms
Chemical equations must be balanced to obey the LAW!
Section 2 – Balancing Chemical EquationsSection 2 – Balancing Chemical Equations
Word Equations
“Sodium carbonate reacts with calcium chloride to produce sodium chloride and calcium carbonate”
Chemical Equations
Na2CO3 + CaCl2 NaCl + CaCO3
This is NOT balanced
Na2CO3 + CaCl2 NaCl + CaCO3
When balancing equations, never change subscripts.
Instead, add coefficients
2
subscripts coefficient
When balancing equations, never change subscripts. Instead, add coefficients
H2 + O2 → H2O22
Al + F2 → AlF32 23
NaClO3 → NaCl + O22 2 3
More on Chemical EquationsSymbols Used in Chemical Equations
Symbol Explanation
(s), (l), (g) Designates a reactant or product in the solid state, liquid state, or gaseous state; placed after the formula
(aq) Designates an aqueous solution; the substance is dissolved in water; placed after the formula
Indicates that heat is supplied to the reaction
A formula written above or below the yields sign indicates its use as a catalyst (in this example, platinum).
Δ
heat
Pt
or
Catalyst – substance that speeds up a chem. rxn but is not part of the chem. equation
Balancing Equations Help…
1. Balance 1 element at a time, from left to right.
2. Treat any polyatomic ions as single units if they are on both sides of the reaction.
Zn(OH) 2 + H3PO4 → Zn3(PO4)2 + H2O3 2 6
(OH) is NOT on both sides
There is a (PO4) on each side
Balancing Equations Hints…
3.Odd # atoms → even # atoms; multiply through by 2
4. Balance oxygen last, it just helps sometimes.
CH3OH + O2 → CO2 + H2O22 24
3
5. Remember, N2, O2, F2, Cl2, Br2, I2, H2
Quiz #1
1. FeCl3 + H2S → FeCl2 + HCl + S
2. MnO2 + HCl → MnCl2 + H2O + Cl2
3. Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed are aqueous sodium
chloride, water, and carbon dioxide gas. Write a skeleton equation for this chemical reaction.
Balance the following chemical equations
Most chemical rxns will fit into 1 of 5 types.
1. Combination (Synthesis)
2. Decomposition
3. Single Replacement
4. Double Replacement
5. Combustion
Section 3 – Types of Chemical EquationsSection 3 – Types of Chemical Equations
1. Combination
A + B → AB
Magnesium metal and oxygen gas combine to form the compound magnesium oxide.
2Mg(s) + O2 (g) → 2 MgO(s)
2. Decomposition
AB → A + B
2HgO(s) 2Hg(l) + O2(g)heat
3. Single Replacement
A + BC → AB + C
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
4. Double Replacement
AB + CD → AC + BD
5. Combustion
A substance reacts with oxygen (O2) and releases energy
If the substance is a hydrocarbon, then CO2 and H2O are products,
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
Which type of reaction?
2K(s) + Cl2(g) → 2KCl(s)
S(s) + O2(g) → SO2(g)
2Fe(s) + 3S(g) → Fe2S3(s)
2NaN3(s) → 2Na(s) + 3N2(g)
H2O H2(g) + O2(g)electricity
K2CO3(aq) + BaCl2(aq) → 2KCl(aq) + BaCO3(s)
2KI(aq) + Pb(NO3)2(aq) → PbI2 + 2KNO3(aq)
Zn(s) + Cu(NO3)2(aq) → Cu(s) + Zn(NO3)2(aq)
Cl2(aq) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)
2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(g)
2Mg(s) + O2(g) → 2MgO(s)
Cu(s) + S(s) → CuS(s)
a) Al + F2 → AlF3
b) C3H8 + O2 → CO2 + H2O
c) FeSO4 + Ba(OH)2 → Fe(OH)2 + BaSO4
d) NaClO3 → NaCl + O2
Can you balance these?
Section 4 – Writing Chemical EquationsSection 4 – Writing Chemical Equations
Common acids:
H2SO4 – sulfuric acid
HCl – hydrochloric acid
HNO3 – nitric acid
Diatomic Molecules:
H2, N2, O2, F2, Cl2, Br2, I2
If the substance combusting is a hydrocarbon, then CO2 and H2O are products.
Write a balanced chemical equation for the combustion of propane (C3H8).
Write a balanced chemical equation for the combination of hydrogen gas and oxygen gas to form water.
Write a balanced chemical reaction for the decomposition of copper(II) hydroxide into copper(II) oxide and water.
Write a balanced chemical equation for the double replacement reaction of sodium nitrate with calcium chloride.
Write a balanced chemical equation for the single replacement reaction of sodium metal with water to form sodium hydroxide and hydrogen gas.
4Ag + O2 → Ag2O2
What does a coefficient mean?
_____ atoms of Ag will react with _____ molecule(s) of O2 to form _____ formula units of Ag2O
A coefficient represents the combining ratio of reactants & products in a chemical rxn.
Exploratory info for next chapters…
4 Ag + O2 → Ag2O21. How many molecules of oxygen (O2) would be needed to react with 4 atoms of silver?
2. How many molecules of oxygen (O2) would be needed to react with 8 atoms of silver?
3. How many formula units of silver oxide would be formed in 1? In 2?
Exploratory info for next chapters…
4 Ag + O2 → Ag2O2
How many oxygen molecules would be needed to form 20 formula units of silver oxide?
How many atoms of silver would be required as well?
Exploratory info for next chapters…
4 Ag + O2 → Ag2O2
If 20 atoms of silver react with 20 molecules of oxygen, which reactant would be used up completely? Which reactant would be leftover?
How many formula units of silver oxide would be formed?
Exploratory info for next chapters…
Limiting Reactant -
Reactant that is completely used up; limits the amount of product that can be produced.
Excess Reactant -
Reactant that remains un-reacted; is not completely used up.
Exploratory info for next chapters…
1. How many molecules of CO are needed to produce 4 atoms of Fe?
6 CO molecules
Fe2O3 + CO → Fe + CO23 2 3
2. How much Fe2O3 is assumed to be present in the question above?
Assuming that there is at least 2 formula units of Fe2O3
Exploratory info for next chapters…