1. Chemistry – Feb 20, 2019 ID chemical reactions
P3 Challenge – (do only one)
Nomenclature quiz (for some)
May use own periodic table
No other resources
Polyatomic ion quiz (for some)
Objective –
New Unit 5 – Reactions
Balancing Reactions
Agenda
ID chemical reactions
Chemical equation notation
Balance equations
Write equations from word descriptions
Assignment:
Balancing Reactions Worksheet (Skip instructions for Blank on left on p2. Just balance.)

2. 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)

3. 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) optional
Large numbers in front of each formula are called coefficients and are necessary to balance the equation.

4. Balancing Chemical Equations
Because of the law of conservation of mass, the same number and types of atoms must be present on both sides of a chemical equation.
Atoms are neither created nor destroyed in a chemical reaction but only reorganized.
Balance an equation by adding coefficients in front of chemical formulas as needed.
DO NOT ADD OR CHANGE FORMULA SUBSCRIPTS!
(Verify all formulas are correct before balancing.)

5. Balancing Chemical Equations
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.
Ex: _____Li2O + _____H2O _____LiOH

6. Some strategies and hints
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
_____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
Hint: 9 molecular elements: H2, N2, O2, F2, Cl2, Br2, I2, P4, S8
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. Exit Slip - Homework _____Fe2O3 + _____C  _____CO + _____Fe
Exit Slip: Balance the following chemical equation:
_____Fe2O3 + _____C  _____CO + _____Fe
What’s Due? (Pending assignments to complete.)
Complete Balancing Reactions Worksheet p 1-2 only (Skip instructions for Blank on left on p2. Just balance.)
What’s Next? (How to prepare for the next day)
Read p