Date post: | 18-Nov-2014 |
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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
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 contain the correct formulas for the reactants and
products.
Na2CO3
The law of conservation of mass must be satisfied.
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
11. Same atoms in reactants as the products