chp 8 pg 240. a. describing chemical reactions 1. intro: a. chem reaction – one or more substances...

CHEMICAL EQUATIONS AND REACTIONS

Chp 8 pg 240

I. CHEM EQUATIONS AND REACTIONS

A. Describing Chemical Reactions1. Intro:

a. Chem reaction – one or more substances is changed into one or more different substances

b. Reactants – before reactionc. Products – after reaction

2. Indications of a Chemical Reactiona. Temperature change and light

- Burning somethingb. Production of gas

- Baking soda and vinegarc. Formation of a precipitate

- Fig 8-2b pg 242d. Color change

- Rusting

3. Characteristics of Chemical Equationsa. Equation must represent known factsb. Equation must contain correct formulas for reactants and productsc. Conservation of mass is met

1) Balance your equation2) Use coefficients

4. FORMULAS TO KNOW CH4 = Methane NH3 = Ammonia CO2 = Carbon dioxide CaCO3 = Calcium carbonate SiO2 = Sand (silicon dioxide) NaF = Sodium fluoride NaCl = Table salt HCl = Hydrochloric acid H2O = Water

5. DIATOMIC MOLECULES

Hydrogen = H2

Nitrogen = N2

Oxygen = O2

Fluorine = F2

Chlorine = Cl2 Bromine = Br2

Iodine = I2

6. Balancing Chemical Equations

a. Has to follow conservation of massb. Do this by adding coefficientsc. Reactant elements must = product elementsd. Steps

1) Work on one atom at a time2) Start with elements that only

appear once3) H and O atoms should be done

last

___H2O ___H2 + ___O2

_2_H20 ___H2 + ___O2

_2_H2O _2_H2 + __O2

Zn + HCl ZnCl2 + H2

Al4C3 + H2O CH4 + Al(OH)3

7. Word and Formula Equationsa. Write the equation using words firstb. Then put in symbolsc. Balance equation

Methane and oxygenmethane + oxygen carbon dioxide +

waterCH4 + O2 CO2 + H2O

CH4 + 2O2 CO2 + 2H2O

8. Additional symbols a. = yieldsb. = Reversible (products can reform reactants)c. ∆ = Reactants are heated

d. Catalyst – speeds up reaction but is NOT used up

Examples

3Fe(s) + 4H2O(g) Fe3O4(s) + O2(g)

2HgO ∆ 2Hg + O2

Write word and formula equations for the chemical reaction that occurs when solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Make sure the formula is balanced.

Sodium oxide + water sodium hydroxide Na2O + H2O NaOH

Solid calcium reacts with solid sulfur to produce solid calcium sulfide.

Ca + S8 CaS

Hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas.

H2 + F2 HF

9. Significance of a Chemical Equationa. Coefficients indicate relative amounts of reactants and productsb. Coefficients also represent moles

H2 + Cl2 2HCl

1molecule H2 : 1molecule Cl2 : 2 molecules HCl1mol H2, 1 mol Cl2, 2mol HCl

c. Relative masses can be determined from coefficients; use moles to convert to gramsd. Reverse reaction has same relative amounts as forward reactione. Don’t tell you:

1) If the reaction will happen2) How fast the reaction will take

place

B. TYPES OF REACTIONS

1. Synthesis Reactionsa. 2 or more substances combine to

form a new compoundb. A + X AXc. 2Mg + O2 2MgO

d. 2H2 + O2 2H2O

BURNING MAGNESIUM

2. Decomposition Reaction a. Single compound broken down into simpler compoundb. AX A +Xc. 2H2O 2H2 + O2

d. Electrolysis – decomposition of substance by electric current

ELECTROLYSIS OF WATERDemo pg 250

3. Single-Replacement Reactiona. 1 element replaces anotherb. A + BX AX + Bc. 2Na + 2H2O 2NaOH +H2

d. Mg + 2HCl H2 + MgCl2

4. Double Replacement Reactiona. 2 elements of a compound switch placesb. Usually forms a precipitate, gas, or waterc. AX + BY AY + BXd. FeS + 2HCl H2S + FeCl2

5. Combustion Reactionsa. Substance combines with oxygen releasing energy as light and heatb. Produces water vapor c. C3H8 + 5O2 3CO2 +4H2O

d. Exothermic – gives off heat6. Endothermic – absorbs heat

DEMONSTRATIONS:

Ethyl alcohol in bottle/jug Zn in HCl w/ballon over beaker to catch

gas – light balloon Tennis ball canon