Chap 8: Chemical Equation and Reaction

8.1 Describing Chemical Reactions1. What is chemical reaction?

2. What are the evidences that a chemical reaction is taking place?

Physical change vs. Chemical change

Chemical ChangePhysical Change

Physical Changes Chemical Changes

Aluminum foil is cut in half. Milk goes sour.

Clay is molded into a new shape. Jewelry tarnishes.

Butter melts on warm toast. Bread becomes toast.

Water evaporates from the surface of the ocean.

Rust forms on a nail left outside.

A juice box in the freezer freezes. Gasoline is ignited.

Rubbing alcohol evaporates on your hand.

Hydrogen peroxide bubbles in a cut.

 Food scraps are turned into compost in a

compost pile.

  A match is lit.

 You take an antacid to settle your

stomach.

  Your body digests food.

  You fry an egg.

I. Describing Chemical Change

• Word equation?– Reactants Products– Read as:

– Ex: Iron + oxygen Iron(III)oxide– Read as:

– ex: hydrogen peroxide water + oxygen

• Chemical Equation:– Skeleton equation-

– Physical states can be identified as-• (s)• (l)• (g)• (aq)

– Additional symbols: see Table 8-2 • catalyst

– Ex. Match maker

Equation can show physical state and reaction conditions

H2 (g) + O2 (g) H2O (l)

H2 + O2 balloon rxn

• When solid aluminum oxide and hydrogen gas are heated, molten aluminum and water vapor form. – Write a word equation for the above reaction

– Write an unbalanced formula using all appropriate symbols (skeleton equation)

Aluminum = Oxygen =

Aluminum Oxide =

Check your understanding!• Describe how both chemical and physical

changes occur in your mouth when you chew food

• How might you use a magnet to show that a completely rusted iron name has undergone a chemical change?

• Magnesium oxide forms from magnesium metal and oxygen gas. Write a word equation and unbalanced formula equation. Include all appropriate notations.

VII. Balancing Chemical Equations

A. Chemical equations must be balanced due to the Law of Conservation of _____. (_________). Reactants are written on the left of the arrow, ________ are written to the right of the arrow. ________________________

B. Equations are balanced by changing __________, not by changing __________. For now all equations will be balanced using ______ numbers.

C. Certain elements will are found as _______ molecules in nature. In a chemical equation, they will be written in this form. The elements are easily remembered by learning the name of the German guy: Mr. __________. The seven diatomic molecules are:___, ___, ___, ___, ___, ___, and ___.

Lavoisier

Balancing Chemical Balancing Chemical EquationsEquations

Mr. HOFBrINClMemorize: H2, N2, F2, O2, I2, Cl2, Br2

O, HuCklBerryFIN

D. Coefficients: Small, ______ numbers placed before the chemical formula. They are multiplied by each atom in the compound.

E. Law of Conservation of Mass: Matter cannot be _______ nor _________, so reactions must be _________.

F. Tips for balancing equations:1. Number of atoms of _________ must equal number of

atoms of ________.2. Coefficients are whole numbers written at the _________ of

the substances.3. All atoms are __________ by the coefficients.4. Subscripts are ______ changed.5. Keep polyatomic ions together as a _______ if unchanged

from reactants to products.6. Balance single elements _____.7. Use the even/odd rule.8. If an element is in _______ compounds, balance that

element last.

Example: Lighting a match:

 

1. Observations:

2. Word Equation:

 

  3. Skeleton Equation:

  P4 + _______________+________

 

4. Balanced Equation:

phosphorus + potassium chlorate potassium chloride + diphosphorus pentoxide

• Balancing Chemical Eq’n:– each side of the eq’n has the same number of

atoms• ex: write the word eq’n for making a bike:

______ + _______ + _________ + _____ bicycle

• write a skeleton eq’n for it using symbols

_____ + _____ + _____ + _____ _______

• use coefficients which are numbers in front of the symbols to balance the equation.

Ex.1: carbon reacts with oxygen gas to produce carbon dioxide:

already balanced- 1: 1: 1

Ex.2: hydrogen gas reacts with oxygen gas to produce water:

balanced ratio- 2: 1: 2

C + O2 CO2

C

O

H2 + O2 H2O

H

O

fig. 8.4 p. 249 Interpreting a Chemical Reaction

How many molecules are on each side? How many How many molecules are on each side? How many moles?moles?

What is total mass of reactants? Of products?What is total mass of reactants? Of products?

Is the reaction balanced?Is the reaction balanced?

Balance the following equations

• ZnS + O2 ZnO + SO2

• Fe2O3 + CO Fe + CO2

• AgNO3 + AlCl3 AgCl + Al(NO)3

1. ___NaClO3 ___NaCl + ___O2

2. ___Fe3O4 + ___H2 ___Fe + ___H2O

Sample Problems:1. Hydrogen + oxygen water

2. Zinc + hydrochloric acid zinc chloride + hydrogen

3. Copper + silver nitrate cupric nitrate + silver

4. Ferric hydroxide iron (III) oxide + water

5. Ethane (C2H6) + oxygen carbon dioxide + water

6. Calcium + water calcium hydroxide + hydrogen

7. Potassium + sulfuric acid potassium sulfate + hydrogen

8. Calcium nitrate + aluminum sulfite calcium sulfite + aluminum nitrate

9. Phosphoric acid is formed when crystalline diphosphorus pentoxide is dissolved in water.

Reaction TypesReaction Types

Combination (Synthesis) Combination (Synthesis) ReactionsReactions

Two or more substances combine to form a new compound.

Reaction of elements with oxygen and sulfur Reactions of metals with Halogens Synthesis Reactions with Oxides There are others not covered here!

Decomposition ReactionsDecomposition ReactionsA single compound undergoes a reaction that produces two or more simpler substances

Decomposition of: Binary compounds H2O(l ) 2H2(g) +

O2(g) Metal carbonates CaCO3(s) CaO(s) +

CO2(g) Metal hydroxides Ca(OH)2(s) CaO(s) +

H2O(g) Metal chlorates 2KClO3(s) 2KCl(s) +

3O2(g) Oxyacids H2CO3(aq) CO2(g) + H2O(l

)

Classify the following reactions as synthesis or Classify the following reactions as synthesis or decomposition: decomposition:

HH22 + Br + Br22 2HBr2HBr

SynthesisSynthesis

AlAl22(CO(CO33))33 AlAl22OO33 + 3CO + 3CO22

DecompositionDecomposition

4 Al + 3C 4 Al + 3C AlAl44CC33

SynthesisSynthesis

Combustion ReactionsCombustion ReactionsA substance combines with oxygen, releasing a large amount of energy in the form of light and heat. Reactive elements combine with oxygen

(This is also a synthesis reaction)

The burning of natural gas, wood, gasoline

Single Replacement ReactionsSingle Replacement Reactions

Replacement of:

Metals by another metal Hydrogen in water by a metal Hydrogen in an acid by a metal Halogens by more active halogens

The Activity Series The Activity Series of the Metalsof the Metals

Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead HydrogenHydrogen Bismuth Copper Mercury Silver Platinum Gold

Metals can replace other metals provided that they are above the metal that they are trying to replace

Metals above hydrogen can replace hydrogen in acids.

Metals from sodium upward can replace hydrogen in water

The Activity Series of the HalogensThe Activity Series of the Halogens

Fluorine Chlorine Bromine Iodine

Halogens can replace other halogens in compounds, providedthat they are above the halogen that they are trying to replace.

Double Replacement ReactionsDouble Replacement ReactionsThe ions of two compounds exchange places in an aqueous solution to form two new compounds.

One of the compounds formed is usually a precipitateprecipitate, an insoluble insoluble gas gas that bubbles out of solution, or a molecular compoundmolecular compound, usually water.

Single or Double Replacement?

2Al + 3H2Al + 3H22SOSO44 Al Al22(SO(SO44))33 + 3H + 3H22

SingleSingle

NaNa22SOSO44 + 2AgNO + 2AgNO33 Ag Ag22SOSO44 + 2NaNO + 2NaNO33

DoubleDouble

3C + Fe3C + Fe22OO33 2Fe + 3CO 2Fe + 3CO

SingleSingle

Examples: Determine the product and reaction type

• H2 + O2

• H2O

• Zn + H2SO4

• HgO

• KBr +Cl2

• AgNO3 + NaCl

• Mg(OH)2 + H2SO3