1. Chemical equations and reactions
Chapter 8.1

2. Objectives:
List three observations that suggest that a chemical reaction has taken place.
List three requirements for a correctly written chemical equation.
Write a word equation and a formula equation for a given chemical reaction.
Balance a formula equation by inspection.
3. Describing Chemical Reactions
Chemical reaction
Defined as the process by which one or more substance are changed into one or more different substances.
Reactants: original substances
Products: resulting substances
According to law of conservation of mass:
total mass of reactants must equal total mass of products

Chemical equation

4. Defined asrepresents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction. 5. Example:this chemical equation shows the reactant ammonium dichromate yields the products nitrogen, chromium(III) oxide, and water(NH4)2Cr2O7(s)N2(g) +Cr2O3(s)+4H2O(g)
6. Indications of Chemical Reactions
Evolution of heat and light
Production of gas
Formation of a precipitate
Color change
Chemistry comes alive!
7. Characteristics of Chemical Equations
Equation MUST represent known facts.

Must be actual chemical reaction

MUST contain the correct formulas for the reactants and products.

Sodium Carbonate

Na2CO3
The law of conservation of mass must be satisfied.

Same number of atoms on reactant side as on the product side.

8. Coefficients are added where necessary 9. Specifies relative number of moles of that substanceEx:Hydrogen gas reacts with oxygen gas to yield water
H2 +O2 H2O
2
2
10. 2
H2 +O2 H2O
2
H O
H O
H
H
H - H
O = O
H - H
4 Hs
2 Os
2 Os
4 Hs

Satisfies the law of conservation of mass

11. Same atoms in reactants as the products