1. Ch. 8 Chemical Equations and Reactions
8.1 Describing Chemical Reactions

2. Chemical Reactions when a substance changes identity
reactants- original
products- resulting
law of conservation of mass
total mass of reactants = total mass of products

3. Chemical Reactions chemical equation
represents identities and relative amounts of reactants and products in the chemical reaction
uses symbols and formulas

4. Hints of Chemical Rxn heat or light gas bubbles precipitate
can also happen with physical changes
gas bubbles
means a gas is being created as product
precipitate
solid is being created
color change

5. Writing Chemical Equations
most pure elements
written as elemental symbol
diatomic molecules
molecule containing only 2 atoms
some elements normally exist this way
H2, O2, N2, F2, Cl2, Br2, I2
other exceptions
sulfur: S8
phosphorus: P4

6. Word Equations uses names instead of formulas
helps you to write formula equation

7. Example
Description:
Solid sodium oxide is added to water at room temperature and forms sodium hydroxide.
Word Equation:
sodium oxide + water  sodium hydroxide
Formula Equation:
Na2O + H2O  NaOH
Na2O + H2O  2NaOH

8. Symbols Used in Equations
yields reversible above arrow: or heat heated MnO2 or Pt catalyst 25°C specific T requirement 2 atm specific P requirement
after a formula: (s) solid (l) liquid (aq) aqueous: dissolved in water (g) gas

9. Coefficients whole numbers in front of formula
distributes to numbers of atoms in formula
specifies the relative number of moles and molecules involved in the reaction
used to balance the equation

10. Equations cannot tell us:
if the reaction will actually occur
depends on many factors affecting energy
the speed of the reaction
depends on chemical kinetics
can be very slow, almost unnoticeably
how the bonding actually changes
formula may not clearly show bonding