1. Chemistry – Jan 23, 2017 P3 Challenge – Today’s Objective –
Write the chemical formula for
calcium hydroxide
hydrochloric acid
calcium chloride
Today’s Objective –
Balancing Reactions

2. Chemistry – Jan 23, 2017 Objective – Balancing Reactions Assignment:
Balancing Reactions Worksheet
Agenda
ID chemical reactions
Chemical equation notation
Balance equations
Write equations from word descriptions
5 types of reactions

3. Evidence of a possible chemical reaction (review)
Color change (ex: rust formation)
Formation of a solid (ex: hard water deposits)
Formation of a gas (ex: Alka Seltzer)
Emission of light (ex: fireworks)
Spontaneous exchange of heat (heats up or cools down) (ex: hot/cold packs)
These observations usually indicate a chemical change
Phase changes also involve the formation of a solid or a gas,
usually only due to heat addition/subtraction, not mixing another substance

4. Chemical Equations
Chemical reactions are represented symbolically using chemical equations
Ex: 2 C2H6 (g) O2 (g)  4 CO2 (g) H2O (g)
The substances mixed together are called reactants. Their chemical formulas are listed with a + sign between them.
Then an arrow represents the process of reacting. Any additional information about the reaction process may be written above or below the arrow. (Heat, light, catalyst…)
The substances produced from the reaction are called products. Their formulas are listed with a + sign between them.
Often, the state of each substance is stated in parentheses. (s, l, g, aq)
Large numbers in front of each formula are called coefficients and are necessary to balance the equation.

5. Balancing Chemical Equations
Because of the conservation of mass, the same number and types of atoms must be present on both sides of a chemical equation.
Balance an equation by adding coefficients in front of chemical formulas as needed. (DO NOT CHANGE FORMULA SUBSCRIPTS!)
How to balance:
1. Make an inventory of the number and type of each type of element on each side of the equation.
2. Balance one element. Update the inventory.
3. Repeat for each element until all elements are balanced.
4. Verify each type of atom is balanced.

6. Some strategies
Avoid balancing an element that occurs in multiple compounds on one side until later. These elements often balance when other elements balance.
Balance a free element last.
When there is not a simple multiple of the numbers, try swapping numbers.
When balancing a last diatomic element that needs an odd number of atom, double all other coefficients and then balance the diatomic.

7. Balancing equations Examples
_____Li2O + _____H2O ---> _____LiOH
_____NH3 + _____NO --->_____ N2 + _____H2O
_____FeCl3 + _____NH4OH ---> _____Fe(OH)3 +_____NH4Cl
_____C5H12 + _____O2 ---> _____CO2 + _____H2O

8. Balancing practice _____ H2 + _____ O2  _____ H2O
_____ Fe + _____ Cl2  _____ FeCl3
_____ Cu + _____ AgNO3  _____ Cu(NO3)2 + _____ Ag
_____ Zn + _____ HCl  _____ ZnCl2 + _____ H2
_____ Pb(NO3)2 + _____ AlCl3  _____ PbCl2 + _____ Al (NO3)3
_____ LiClO3  _____ LiCl + _____ O2
_____ Mg(OH)2 + _____ HCl  _____ MgCl2 + _____ H2O

9. Word Equations
When solid sodium metal reacts with liquid water, an aqueous solution of sodium hydroxide and hydrogen gas are formed.
When aqueous calcium chloride and aqueous sodium sulfate are mixed a white solid of calcium sulfate forms in an aqueous solution of sodium chloride.
The reaction of aqueous silver nitrate and aqueous sodium chromate that forms solid silver chromate and aqueous sodium nitrate.

10. Types of reactions Synthesis (Combination) Decomposition
A + B  AB Two elements react to form a compound
Decomposition
AB  A + B A compound is separated into its elements
Single Replacement
A + BC  AC + B One element takes the place of another in a compound.
Double Replacement
AB + CD  AD + CB Ionic partners switch

11. Combustion
The reaction with oxygen is so common that it is often given its own classification: combustion.
The products of a combustion are always the oxides of the elements in the other reactant. If there is a choice of metal ion, you will be told what ion charge to use.
Ex: Fe + O2  Fe2O3
Ex: CH4 + O2  CO2 + H2O
Ex: Li + O2  Li2O
Classify each of the reactions
from previous slides.

12. Reaction Types Overview
Reactants
Reaction Type
Products
Two elements
Synthesis (S)
Compound of the two elements
A single compound
Decomposition (D)
Component elements (or simpler substances)
An element and a compound
Single replacement (SR)
Different element and compound
Two compounds
Double replacement (DR)
Two different compounds
Reaction with oxygen
Combustion (C)
Oxides of each element in other reactant

13. Exit Slip - Homework
Exit Slip: Balance the following chemical equation:
_____Fe2O3 + _____C  _____CO + _____Fe
What’s Due? (Pending assignments to complete.)
Complete the Balancing Reactions Worksheet
What’s Next? (How to prepare for the next day
Read p