1. Chemical Equations

2. Chemical Versus Physical Change
chemical change – new substance forms w/ properties that differ from original sub. (rusting, oxidizing)
Lab test needed to be sure
physical change - does not change id. of a sub
Δ of state (evaporation, melting, subliming)

3. Chemical Reactions
chemical rxn- process by which 1 or more substances change into 1 or more new subs.
Reactants -original sub. (before )
Products –sub. created. (after )

4. Evidence of a Chemical Reaction

5. Evidence of a Chemical Reaction
color changes, bubbles (gas)

6. Reactions and Energy Changes
Exothermic rxn. -Energy is released as product.
CH4 + O2  CO2+ H2O + energy
Endothermic rxn. -Energy is absorbed as reactant.
N2O4 + energy  NO2

7. Constructing a Chemical Equation
chemical equation shows formulas and relative amounts of all reactants and products.

8. Diatomic molecules: H2,O2,N2,F2, Cl2,Br2,I2
(BrINClHOF)-mnemonic
H + 7 on periodic table

9. Equations and Reaction Information

10. Equations and Reaction Information
Physical States
NaHCO3(s) + HC2H3O2(aq)  NaC2H3O2(aq) + CO2(aq) + H2O(l)
solid liquid
aqueous solutions
Reaction Conditions
350°C, kPa
N2(g) + 3H2(g)
2NH3(g)
Mn or Pd

11. methane + oxygen  carbon dioxide + water
Writing a Word Equation and Formula Equation
A word eq. contains names.
Ex. carbon dioxide and water are produced when methane gas reacts with oxygen. Write a word equation and an unbalanced formula equation w/ states of substances.
methane + oxygen  carbon dioxide + water

12. Atom Inventories
Counts the number of each kind of atom on both sides of the equation.
If same number of each atom on both sides of the equation, it is balanced.
CH4 + 2O2 → CO2 + 2H2O
2KI + 4Pb(NO3)2→ 5PbI2 + 2KNO3