1. Chemical Reactions Chapter 11
SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions.
SC2.a. Identify and balance the following types of chemical equations:
Synthesis, Decomposition, Single Replacement, Double Replacement, and Combustion
SC2.b. Experimentally determine indicators of a chemical reaction specifically precipitation, gas evolution, water production, and changes in energy to the system.

2. Writing chemical Equations
In chemical reactions one or more reactants change into one or more products.
Chemists use a chemical equations to convey a s much information as possible about what happens in a chemical reaction.
The reactants are written on the left and the products on the right
An arrow separates them, read the arrow as yields, gives, or reacts to produce.
Reactants → products
example: iron + oxygen → iron (III) oxide

3. Writing chemical Equations
To write word equations, write the names of the reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.
Example: hydrogen peroxide decomposes to form water and oxygen gas
Hydrogen peroxide → water + oxygen
Chemical equation is a representation of a chemical reaction
Skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products.
Write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right.

4. Writing chemical Equations
You can indicate the physical states of substances by putting a symbol after each formula: (s) = solid, (l) = liquid, (g) = gas, and (aq) = aqueous solution [a substance dissolved in water]
Example: Fe (s) + O2 (g) → Fe2O3 (s)
Catalyst is a substance that speeds up the reaction but is not used up in the reaction.
A catalyst is neither a reactant nor product and is written above the arrow.

6. Types of equations Word equation Skeletal equation
Carbon Dioxide + Water  Glucose + Oxygen
Skeletal equation
CO2 + H2O  C6H12O6 + O2
Skeletal equation with phases
CO2 (g) + H2O (l)  C6H12O6 (s) + O2 (g)
Balanced equation
6CO H2O  C6H12O O2

7. Types of Reactions
Combination (synthesis) reaction is a chemical change in which two or more substance react for form a SINGLE NEW SUBSTANCE.
Example: 2H2 + O2 → 2H2O
Combination reactions are easy to recognize because they have two reactants and one product.
Decomposition reaction is a chemical change in which ONE SUBSTANCE reacts to form TWO or more new substance.
Example: 2H2O → 2H2 + O2
Decomposition reactions are easy to recognize because they have one reactants and two or more products.

8. Types of Reactions
3. Single replacement reaction is a chemical change in which ONE ELEMENT replaces another element in a COMPOUND.
you can recognize a single replacement reaction because both the reactant and the product have an element and a compound
example: 2K + 2H2O → 2KOH + H2
4. Double-replacement reaction is a chemical change involving an exchange of positive ions between two compounds.
you can recognize a double-replacement reaction because both the reactants and the products are two compounds
They generally take place in aqueous solutions, and often produce a precipitate, a gas, or a molecular compound such as water.
FeCl3 + NaOH → Fe(OH)3 + NaCl

9. Types of Reactions
5. Neutralization Reaction is a special type of double-replacement reaction. It is a chemical change where an acid and a base react to form water and a “salt”
Most bases are hydroxides, example: sodium hydroxide {NaOH}
Most acids start with hydrogen, example: hydrochloric acid {HCl}, sulfuric acid {H2SO4}
Salts are defined as ionic compounds
Example: NaOH + HCl → H20 + NaCl
6. Combustion reaction is a chemical change in which an element or a compound reacts with oxygen often producing energy in the form of heat and light.
Often the other reactant is a hydrocarbon or an alcohol and the products are carbon dioxide and water.
Example: CH4 + O2 → CO2 + H2O

10. Types of Reactions Summary
Type of Reactants
Reaction Type
Products
2 elements ONLY
Combination or synthesis
Compound
1 compound ONLY
Decomposition
Elements
C, H, O and O2 ONLY
Combustion
CO2 + H2O ALWAYS
1 element and 1 compound
Single replacement
1 compound and 1 element
2 compound
Double Replacement
2 compounds
Acid + Base
Neutralization
H2O + “salt”

11. Types of Reactions Practice
Al + CH3OH  (CH3O)3Al + H2
Ba(NO3)2 + CuSO4  BaSO4 + Cu(NO3)2
N H2  NH3
H2O (l) + SO3 (s)  H2SO4 (aq)
KOH + H3PO4  K3PO4 + H2O
C4H10 + O2  CO2 + H2O
H2O2  H2O + O2
KI + Cl2  KCl + I2
AgNO3 + KCl  AgCl(s) + KNO3
NaHCO3(s)  Na2CO3(s) + H2O(l) + CO2(g)
Single Replacement
Double Replacement
Combination
Neutralization
Combustion
Decomposition
Double replacement

12. Balancing chemical Reaction
The law of conservation of mass states that matter is not created or destroyed it merely changes forms.
In order to show that mass is conserved the amount of products and reactants MUST equal.
Once a word equation is turned into chemical formulas it must be balanced.

13. Balancing Chemical Equations
Coefficients are small whole numbers that are placed in front of the formulas in an equation in order to balance it.
Balanced equation is a chemical equation in which each side of the reaction has the same number of atoms of each element and mass is conserved.
To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.
In every balanced chemical equation each side of the equation has the same number of atoms of each element.

14. Steps to balancing chemical equations
Create a T-chart and List the elements in the chemical formulas on each side in the SAME order
Count the number of atoms of each element on each side
See what elements don’t match in your T-chart
Add coefficients in front of one substance at a time,
Start by balancing the most complex compound first,
general rule of thumb is to save Hydrogen and Oxygen until the end to balance.
recount number of atoms of each element
Repeat 3, 4 & 5 until all elements are balanced.

15. Counting Atoms
In order to balance chemical reactions you MUST first know how to count atoms.
Subscripts multiply what ever they are beside
If a subscript is beside parentheses it multiplies everything in the parentheses.
Coefficients multiply everything immediately behind them.

16. Counting Atoms Practice
H2O
CuSO4
NaHCO3
Cu(NO3)2
(NH4)3PO4
2 H2O
3CuSO4
2 Cu(NO3)2
3 (NH4)3PO4
2 H, 1 O
1 Cu ,1 S,4 O
1 Na, 1 H, 1 C, 3 O
1 Cu,2 N,6 O
3 N, 12 H, 1 P, 4 O
4 H, 2 O
3 Cu, 3 S, 12 O
2 Cu, 4 N, 12 O
9 N, 36 H, 3 P, 12 O

17. Balancing Chemical Reactions Practice
Example 1: N H2  NH3
N | N
H | H
Pick an element to start balancing with, I pick N
Least common multiple between 1 and 2 is 2
Add 2 in front of product side and recount
N is balanced so now look at H
Least common multiple between 2 and 6 is 6
Add 3 in front of reactant H and recount
Now both sides are equal so it is a balanced equation 3 2
= 1
= 3
= 2
= 6
= 2
= 6
= 2

18. Balancing Chemical Reactions Practice
Is a trial and error process
Example 1: NaHCO3  Na2CO3+ H2O + CO2
Na | Na
H | H
C | C
O | O
Count Atoms of each element
Start balancing the most complex item (reactant) 2
Na = | Na = 2
H = 1 | H = 2
C = 1 | C = 1+1 =2
O = 3 | O = = 6
Na = | Na = 2
H = 2 | H = 2
C = 2 | C = 1+1 =2
O = 6 | O = = 6

19. Balancing Chemical Reactions Practice
Is a trial and error process
Example 1: C4H O2  CO H2O
C | C
H | H
O | O
Start balancing the most complex item (reactant)
Leave H and O until the end
Have to use whole number and currently have no whole number… trick: Double all current coefficients and recount.
It is Now Balanced 8 2 13 4 10 5
C = 4 | C = 1
H = 10 | H = 2
O = 2 | O = 2 +1 = 3
C = 4 | C = 4
H = 10 | H = 2
O = 2 | O = 8 +1 = 9
C = 8 | C = 8
H = 20 | H = 20
O = 26 | O = = 26
C = 8 | C = 8
H = 20 | H = 20
O = 2 | O = = 26
C = 4 | C = 4
H = 10 | H = 10
O = 2 | O = 8 +5 = 13

20. Balancing Reaction Practice – Polyatomic
Balancing reactions with polyatomics can be a bit complicated but if the polyatomic is the same on BOTH sides of reaction you can treat it like a special element.
FeBr Ba(OH)2 → BaBr Fe(OH)3
When counting Atoms put a box around JUST the polyatomic
Count like normal and balance using these count
Br is 1st thing that don’t balance, common multiple between 2 and 3 is 6 2 3 3 2
Fe 1 | Fe
Br 3 | Br
Ba 1 | Ba 1
(OH) 2 | (OH) 3
Fe | Fe
Br | Br
Ba | Ba
(OH) | (OH)
Fe | Fe
Br | Br
Ba 1 | Ba
(OH) 2 | (OH) 3
Fe | Fe
Br | Br
Ba 1 | Ba
(OH) 2 | (OH)

21. Balancing Reaction Practice – Polyatomic
Na3PO MgSO4 → Mg3(PO4) Na2SO4
When counting Atoms put a box around JUST the polyatomic
Count like normal and balance using these count
Na is 1st thing that don’t balance, common multiple between 2 and 3 is 6.
Fix each side and recount
Mg is next thing that don’t balance, common multiple between 1 and 3 is 3. 2
Na3PO MgSO4 → Mg3(PO4) Na2SO4 3 3
Na | Na
PO | PO4 2
Mg | Mg 3
SO | SO
Na | Na
PO | PO4 2
Mg 1 | Mg 3
SO4 1 | SO
Na 3 | Na 2
PO4 1 | PO4 2
Mg 1 | Mg 3
SO4 1 | SO4 1
Na | Na 2
PO | PO4 2
Mg 1 | Mg 3
SO4 1 | SO4 1

22. Predicting Products
Predicting the products of a chemical reaction involve 1st determining the type of reaction that is occurring.
Combination: starts with 2 elements
Decomposition: starts with 1 compound
Single Replacement: Starts with 1 element & 1 compound
Double Replacement: starts with 2 compounds
Neutralization: starts with 2 compounds that are an ACID and a BASE
Combustion: starts with O2 and a compound containing C, H and/or O.

23. Predicting Products identifying types of reaction practice.
____Al + ____Cl2  ___Mg(OH)2 + ___HCl ___Zn + ____HCl ___C2H6 + ___O2 ___Al2O3  __Ba(NO3)2 + __Na2SO4 
Combination
Neutralization
Single replacement
Combustion
Decomposition
Double replacement

24. Predicting Products
Predicting the products of a chemical reaction involve next determine the products that would be produced based on a balance of charge.
Combination: ends with 1 compound
Decomposition: ends with 2 elements
Single Replacement: ends with 1 element & 1 compound
Double Replacement: ends with 2 compounds
Neutralization: ends with H2O and a “salt”
Combustion: ends with CO2 and H2O

25. Predicting Products ____Al + ____Cl2 
Is a combination reaction so the product is a compound between aluminum and chlorine. MUST BALANCE CHARGES!
Al+3 and Cl-1 form compound
AlCl3
____Al + ____Cl2  ____ AlCl3 still needs number of atoms to be balanced
___Mg(OH)2 + ___ HCl
Is a neutralization reaction so the product is water and a salt. The salt would be formed between the element at the beginning of the base and the element at the end of the acid. Think square dance!! MUST BALANCE CHARGES!
Mg +2 and Cl-1 form compound
MgCl2 and H2O
___Mg(OH)2 + ___HCl  __ MgCl2 + __ H2O still needs number of atoms to be balanced

26. Predicting Products __Al2O3 
Is a decomposition reaction so the product is just elements.
Don’t forget diatomic elements.
Al and O2 (is a diatomic element)
__Al2O3  __ Al + ___ O2
__Ba(NO3)2 + __Na2SO4 
Is a double replacement reaction, the positive ions switch partners. MUST BALANCE CHARGES!
__Ba(NO3)2 + __Na2SO4  __BaSO4 + __NaNO still needs to be balanced

27. Predicting Products ___Zn + ____HCl
Is a single replacement reaction so the element replaces an element in the compound
Generally the 1st element in compound is the one that leaves. MUST BALANCE CHARGES!
___Zn + ____ HCl ___ZnCl2 + ___H2
___C2H6 + ___O2
Is a combustion reaction, and can only make carbon dioxide and water.
___C2H6 + ___O2 ___ CO2 + _____H2O

28. Predicting Products Summary
Make sure to BALANCE charges for ALL ionic and acid compounds
Transition Metals use the reactant to determine the charge and assume that it stays the same.
Once you BALANCE CHARGES do NOT change the subscripts.
Don’t forget your 7 diatomic elements:
When they are not in compounds they are in pairs
N2, O2, F2, Cl2, Br2, I2, H2
ALL other elements are single elements when not in compounds
Just because an element has a subscript on the reactant side, does NOT mean it will have the same subscript on the product side.

29. Word Equations
When balancing reactions that are word equations you MUST first write BALANCED chemical formulas.
Remember to check the ions that each forms for Ionic compounds and Acids
Once you have a balanced chemical formula DO NOT change the formula (i.e. change subscripts)
DON’T forget your 7 diatomic elements.

30. Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)
Word Equations
Example 1: solid calcium hydroxide reacts with sulfuric acid to produce aqueous calcium sulfate and water.
Pick out the chemical names in the reaction and turn them into chemical formulas
calcium hydroxide + sulfuric acid → calcium sulfate + water
calcium hydroxide = Ca+2 OH-1,
Ca(OH)2
Sulfuric acid = oxy acid,
Sulfuric was sulfate, H+1 SO4-2,
H2SO4
Calcium Sulfate = Ca +2 SO4-2
CaSO4
Water = H2O
Skeleton Equation becomes:
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)

31. Word Equations Balancing Example 1
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)
Remember polyatomic rule only applies if it is the SAME on both sides.
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) H2O (l)
Ca | Ca 1
H | H
O | O
SO | SO4 1
Ca | Ca 1
H | H 2
O | O 1
SO | SO4 1

32. Word Equations
Example 2: Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas.
Don’t forget to balance charges and your 7 diatomic elements
AlBr3 + Cl2 → AlCl Br2
Now Balance Atoms like normal
AlBr3 + Cl2 → AlCl Br2
Al 1 | Al 1
Br 3 | Br 2
Cl 2 | Cl 3
2 AlBr3 + Cl2 → AlCl Br2
Al | Al 1
Br | Br 2 6
Cl 2 | Cl 3
2 AlBr Cl2 → 2 AlCl Br2
Al | Al 1 2
Br | Br 2 6
Cl 2 6 | Cl 3 6