1. Describing & Balancing Chemical Reactions

2. Describing a Chemical Reaction
Reactants =
Products =
In a chemical reaction,

3. Indications of a Chemical Reaction
There are 4 observable changes that indicate that a chemical reaction is taking place: 1. 2. 3. 4.

4. Precipitate Video

5. Characteristics of Chemical Equations
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All reactants and products must be identified.
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Use charges and oxidation states to determine the chemical formulas of the products from the reactants
Recall that charges must cancel—must make sense

6. Characteristics of Chemical Equations
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The same number of each type of atom must appear on each side of the chemical equation
Coefficients =
Ex: 2H2O

7. Symbols Used in Chemical Equations
+ ____________________________________  ____________________________________ ( ) _____________ (s) Reactant or product is a ____________________ (l) Reactant or product is a ____________ (g) Reactant or product is a __________ (aq) Reactant or product is ______________________

8. Writing Chemical Formulas
Chemical reactions can be written as:
Word equations:
Formula equations:
CH4 (g) + O2 (g)  CO2 (g) + H2O (g) (not balanced)

9. Sample Problem #1 Word Equation:
Write the word and formula equations for the reaction that occurs when solid sodium oxide is added to water at room temperature and forms sodium hydroxide (dissolved in water).
Word Equation:
Formula Equation:
Balanced Formula Equation:

10. Significance of a Chemical Equation
Chemical reactions contain quantitative information:
Coefficients indicate relative amounts of reactants and products. (moles)
The relative masses of the reactants and products can be determined.

11. Significance of a Chemical Equation
The:
3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)

12. Balancing Chemical Equations
Steps for balancing chemical equations: 1. 2. 3. 4.

13. Sample Problem #2 __Zn (s) + HCl (aq)  ZnCl2 (aq) + ___ H2 (g)
Zinc reacts with aqueous hydrochloric acid to produce a solution of zinc chloride and hydrogen gas. Write and balance the equation.
__Zn (s) + HCl (aq)  ZnCl2 (aq) + ___ H2 (g)

14. Practice
___C2H4(g) +___ H2(g)  ____ C2H5

15. Practice Balance and Translate to a chemical sentence:
___BaCl2(aq) + ___Na2(CrO4)(aq).  ___Ba(CrO4)(s) + ___NaCl(aq)

16. Practice
Hydrazine, N2H4, is used as rocket fuel. Hydrazine reacts violently with oxygen to produce gaseous nitrogen and water. Write the balanced chemical equation.

17. Practice
Solid aluminum metal reacts with aqueous zinc chloride to produce solid zinc metal and aqueous aluminum chloride. Write the balanced chemical equation.