1. Honors Chemistry Chapter 9
Chemical Equations

2. 9.1 Representing Chemical Changes
Chemical Reaction – the process by which 1 or more substs are changes into 1 or more diff substs
Correct equation shows:
What changes take place
Relative amts of various elems & comps that take part in these changes

3. 9.1 Representing Chemical Changes
Reactants – starting substs ina chemical rxn
Products – substs formed by the chemical rxn
2C2H2(g) + 5O2(g) CO2(g) + 2H2O(l)
Reactants yield products
Letters in ( ) indicate physical state of ea subst involved
(g) – gas, (l) – liquid, (s) or (cr) – solid (crystalline), (aq) – aqueous or water soln

4. 9.2 Balancing Equations To write a correct chemical eqn:
Determine reactants & products
Write reactants on left side connected w/ a + an write products on right side
Connect 2 sides w/ an arrow showing direction of rxn
SYMBOLS & FORMULAS MUST BE WRITTEN CORRECTLY
3. Balance eqn
- show an = # of atoms of ea elem on both sides of the eqn

5. 9.2 Balancing Equations 3. Balance eqn
show an = #of atoms of ea elem on both sides of the eqn
In a chem rxn, mass is not lost or gained
Same amt of matter before & after rxn
Same # & kind of atoms must be present on both sides of an eqn

6. 9.2 Balancing Equations Example:
C3H8 + O CO2 + H2O
C3H O CO H2O
Balance by changing only coefficients, never subscripts!

7. 9.3 Classifying Chemical Changes
6 General Types of Rxns
Single Displacement Rxn
1 elem displaces another in a compound
Ex) Cl KBr KCl + Br2
Ex) 2Al + Fe2O Al2O Fe
General Form:
elem + comp elem + comp
A + BX B + AX
X + AY Y + AX

8. 9.3 Classifying Chemical Changes
Double Displacement Rxn (Ionic Rxn)
The (+) and (-) ions of 2 comps are interchanged
Ex) PbCl2 + Li2SO LiCl + PbSO4
Ex) ZnBr2 + 2AgNO Zn(NO3)2 + 2AgBr:
General Form:
Comp + comp comp + comp Or
AX + BY AY + BX

9. 9.3 Classifying Chemical Changes
Neutralization
A special type of double displ rxn
Acid + Base Salt (ionic comp) + water
Strong acid start w/ H, bases end in OH
Ex) HBr + NaOH NaBr + HOH
Ex) Ba(OH)2 + 2HNO Ba(NO3)2 + 2HOH

10. 9.3 Classifying Chemical Changes
Decomposition
Subst breaks up into simpler substs when energy is supplied
Ex) CdCO CdO + CO2
Ex) Pb(OH) PbO + H2O
General Form:
Comp or more elems or comps
AB A + B
Energy may be heat, light, electricity, or mechanical shock

11. 9.3 Classifying Chemical Changes
Synthesis
2 or more substs combine to form 1 new subst (sometimes called composition rxn)
Ex) NH3 + HCl NH4Cl
Ex) 2H2 + O H2O
General Form:
Elem or comp. + elem or comp comp
A + B AB

12. 9.3 Classifying Chemical Changes
Combustion (of hydrocarbons)
Not usually considered one of the major types of rxns
Most organic comps will burn in air
Many are very flammable
When a comp burns in air, it is really reacting w/ oxygen in air
Combustion rxns are referred to as oxidation rxns
Products of the combustion of a hydrocarbon under normal conditions are CO2(g) & H2O(g)

13. 9.3 Classifying Chemical Changes
Combustion (cont)
Ex) Methane (CH4) burns in air
CH O CO H2O
Ex) Butane (C4H10) burns in air
2C4H O CO H2O
General Form:
Hydrocarbon + oxygen CO2 + H2O

14. 9.4 Mass-Mass Relationships
Balanced eqns represent the relationship betw the # of particles that react & the # of particles produced
There is also a relationship betw reacting masses & masses of products
The coefficients of a balanced eqn give the relative amts in moles of reactants & products.

15. Mass-Mass Relationships
To solve mass-mass problems:
1. Write a balanced eqn
Show rxn that is taking place
2. Start w/ what your given & change to moles of given subst
3. Using ratio of moles in the eqn, go to mole of required subst (what your asked for)
4. Change from moles of required subst to grams
Work out prob (checking units)

16. 9.5 Energy & Chemical Change
Chemical changes are always accompanied by a change in energy
Endothermic – a rxn in which energy is absorbed
Products are higher in energy than reactants
DHr = +
Exothermic – a rxn in which energy is released
Products are lower in energy than reactants
DHr = -

17. 9.5 Energy & Chemical Change
All rxns require a certain minimum amt of energy to get started
- Activation Energy