1. chemical reaction = process by which one or more substances are changed into one or more...

1. Chemical reaction = process by whichone or more substances are changedinto one or more different substances(atoms are rearranged)

a) reactants = original substances(written tothe left of the arrow in a chemical equation)

b) products = resulting substances(writtento the right of the arrow in a chemicalequation)

YieldsReactants

CH4 + 2O2

Products

CO2 + 2H2O

c) Indications of a chemical reaction(chemical change):

– evolution of heat and/or light

– production of a gas (often seenas bubbles)

– color change

– formation of a precipitate whentwo solutions are mixed(Precipitate = a solid thatseparates from a solution)

d) catalyst = a substance that speeds up achemical reaction but is not permanentlyconsumes in the reaction.

–Catalysts DO NOT appear as reactantsor products!

–Ex: manganese dioxide is a catalyst inthe following reaction:

2H2O2 O2 + 2H2OMnO2

1. Chemical equation = a representation ofthe reactants and products in a chemicalreaction

a) Word equation = a chemical equation inwhich the reactants and products in achemical reaction are represented bywords

• Ex:

sodium + water → sodium hydroxide + hydrogen

reactants products

b) Formula equation = a chemical equationin which the reactants and products in achemical reaction are represented bychemical symbols or chemical formulas

• Ex:

Na + H2O → NaOH + H2

reactants products

c) Atom inventory (for a chemical equation)= a “bookkeeping” technique designed tocount the number of each type of atom(ion) represented on each side of achemical equation

d) Subscript = whole number that appearsto the right and below a chemical symbol ina chemical formula (if no number is writtenit is assumed to be “1”)

– Indicates the number of atoms or ions

– Ex: H2O

subscript subscript (assumed to be “1”)

• Coefficient = whole number that appearsin front of a reactant or product in abalanced chemical equation (if no numberis written it is assumed to be “1 1”) )

– Indicates the number of molecules ormoles

• Ex:

• Ex:

2 CO2

coefficient

Al2S3

coefficient (assumed to be “1”)

f) Balanced chemical equation = a formulaequation where coefficients are added soequal numbers of each type of atom (ion)are represented on each side of theequation

• Ex:

+ → 2 NaOH(aq) +2 Na (s) 2 H2O (l) H2(g)

reactants products

2 Na (s) + 2 H2O (l) → 2 NaOH(aq) + H2(g)

• 2 molecules of solid sodium reacts with 2molecules of water to yield 2 molecules ofaqueous sodium hydroxide and 1 molecule ofhydrogen gas.

OR

• 2 moles of solid sodium reacts with 2 moles ofwater to yield 2 moles of aqueous sodiumhydroxide and 1 mole of hydrogen gas.

•

4 Fe + 3 O2 → 2 Fe2O3

4 Fe + 3 O2

• What are the reactant(s)?=

___________________________

• What are the product(s)?

_____________________________2 Fe2O3

• # of moles of O2 =______________

• # of molecules of O2=_____________

# of atoms of Fe in 2Fe2O3 = ________4

• # of atoms of O in 3 O2 =_________

3

3

6

Symbol

Meaning

“yields”;indicates result of areaction

Indicates a reversiblereaction

(s) A reactant or product in theSolid state

↓ Alternative to (s);used only for aPrecipitate (solid) falling out ofsolution

(l) A reactant or product in the liquidstatet

(aq) A reactant or product in aqueousSolution (dissolved in water)

(g) A reactant or product in theGaseous state

↑ Alternative to (g);used only for aGaseous product

Δ Reactants are heated

2atm Pressure at which the reaction isCarried out, in this case 2 atm

O°CTemperature at which reaction isCarried out, in this case O°C

MnO2

A catalyst is used to speed up theReaction rate, in this case MnO2

Would be used to speed up theReaction rate.

1. The equation must represent the knownfacts with all reactants and productsidentified.

2. The equation must contain the correctformulas of the reactants and products.

• A chemical reaction obeys the “Law ofConservation of Matter”

• The Law of Conservation of Matter =matter cannot be either created ordestroyed in ordinary chemical or physicalmeans.

• The Law of Conservation of Matter mustnot be violated!

– This means you must balanceequations. (Equations are balanced byadding coefficients, NOT subscripts.)

4. Why do we balance equations?

–The Law of Conservation of Mattermust not be violated!

5. Atomic theory can be used to explain whychemical reactions obey the “Law ofConservation of Matter”.

– All atoms present at the start of achemical reaction are present at the endof that chemical reaction (atoms aresimply rearranged during a chemicalreaction).

•

–Since no atoms are created or destroyedin a chemical reaction no matter iscreated or destroyed in a chemicalreaction.

–Since no matter is created or destroyedin the chemical reaction the mass of thereactants must equal the mass of theproducts in a chemical reaction.

•

6. A balanced chemical equation details howa chemical reaction obeys the “Law ofConservation of Matter”.

1. Whether the reaction will actually occur.Chemical equations can be written forreactions that do not necessarily takeplace.

2. The speed of a reaction.

3. The pathway atoms or ions take inmoving from reactants to products.

1. Write a word equation

2 2. Write a formula equation

a) remember naturally occurringdiatomic elements:

• H2, O2, N2, Cl2, Br2, I2, F2

b) unless otherwise noted, other elementsare represented by the elementsymbol; ex: magnesium = Mg

c) remember the formulas for acids:

• HCl = Hydrochloric Acid

• HNO3 = Nitric Acid

• H3PO4 = Phosphoric Acid

• CH3COOH = Acetic Acid (NOTE: thepositive ion (H+) is at the end)

• H2CO3 = Carbonic Acid

• H2SO4 = Sulfuric Acid

d) remember the rules for writing formulasfor ionic compounds (ions)

• METALS & NONMETALS!!

e) remember the rules for writingformulas for molecular compounds(prefixes)

• ONLY NONMETALS!!

f) remember the formula for water, H2O

• HOH (hydrogen hydroxide)

3. Write a balanced chemical equation byadding coefficients, NOT subscripts (thiswill require trial and error, the followingguidelines may be helpful)

a) balance the different types of atoms oneat a time

b) first, balance the atoms of elements thatare combined and that appear only onceon each side of the equation

c) balance polyatomic ions that appear onboth sides of the equation as single units

d) balance H atoms and O atoms afteratoms of all other elements have beenbalanced

4. Conduct an atom inventory throughout theprocess. Be sure to conduct an atominventory at the end of the process to becertain you have the correct answer.

5 5. Be certain that the coefficients representthe SMALLEST possible whole numberratio of reactants and products.

6. Common problems when balancingequations:

a) You must write correct formulas!

b) once a correct formula is written,subscripts CANNOT be changed!

a) Hydrogen reacts with oxygen to produce water.

b) Zinc reacts with hydrochloric acid to produce asolution of zinc chloride and hydrogen gas.

c) Aluminum sulfate reacts with calcium hydroxideto form aluminum hydroxide and calcium sulfate.

• 2 or more substances combine to form onenew substance

• General format:

A + B AB

Ex: NH3 + HCl NH4Cl

2 Na + C12 2 NaCl

• Synthesis Practice: For each of thefollowing, predict the products and write aword equation. Next, write a formulaequation and a balanced chemicalequation. Finally, write the type of reactionrepresented by each chemical equation.

a) magnesium + oxygen →

b) sodium + fluorine →

c) magnesium + fluorine →

d) lithium + chlorine →

• HOMEWORK!!

e) barium + oxygen →

• HOMEWORK!!

f) potassium + oxygen →

HOMEWORK!!

• Substances break up or decompose intosimpler substances

• General format:

AB

• Ex:

A + B

H2CO3

2 Al2O3

H2O + CO2

4 Al + 3 O2

• Decomposition Practice: For each of thefollowing, predict the products and write aword equation. Next, write a formulaequation and a balanced chemicalequation. Finally, write the type of reactionrepresented by each chemical equation.

a) water →

b) mercury(II) oxide →

c) magnesium chloride →

• HOMEWORK!!

d) silver oxide →

HOMEWORK!!

• One element replaces another in acompound

• General format:

A + BC

Ex: Cl2 + 2 KBr

2 Na + 2 H2O

AC + B

2 KCl + Br2

2 NaOH + H2

• Single Displacement Practice: For eachof the following, predict the products andwrite a word equation. Next, write aformula equation and a balanced chemicalequation. Finally, write the type of reactionrepresented by each chemical equation.

a) aluminum + lead(II) nitrate →

b) lithium + water →

c) aluminum + sulfuric acid →

d) chlorine + potassium bromide →

e) fluorine + sodium chloride →

f) aluminum + silver nitrate →

HOMEWORK!!

g) barium + water →

HOMEWORK!!

h) lithium + hydrochloric acid →

HOMEWORK!!

• Positive and negative ions are exchanged

• General format:

AB + CD CB + AD

Ex: Ba(OH)2 + H2SO4

AgNO3 + NaCl

BaSO4 + 2 H2O

AgCl + NaNO3

• Double Displacement Practice: For eachof the following, predict the products andwrite a word equation. Next, write a

formula equation and a balanced chemicalequation. Finally, write the type of reactionrepresented by each chemical equation.

a) potassium iodide + lead(II) nitrate →

b) sulfuric acid + sodium hydroxide →

c) silver nitrate + sodium phosphate

d) nitric acid + potassium hydroxide

HOMEWORK!!

e) sulfuric acid + potassium hydroxide

• HOMEWORK!!

f) calcium phosphate + acetic acid

HOMEWORK!!

____________2) 4 Fe + 3 02

___________3) Cl2 + 2 NaBr

_____________ 2 H2O +O2

2 Fe2O3

2 NaCl +Br2

Decomposition 1) 2 H2O2

Synthesis

SingleDisplacement

_____________4) Zn +H2SO4

Displacement 5) Pb(NO )p

ZnSO4 +H2

SingleDisplacement

Double

____________5 3 2 +K2CrO4 PbCrO4 + KNO3

• Reaction rate = the rate (speed) ofdisappearance of a reactant or the rate ofappearance of a product in a chemicalreaction

a) A chemical reaction that takes a longtime to happen has a slow reactionrate.

b) A chemical reaction that takes a shorttime to happen has a fast reaction rate.

1) Nature of reactants

a) Reactions occur at different ratesdepending on the reactants.

b) ) Some reactions occur almostinstantaneously (such as double-replacement reactions).

c) Other reactions occur slower.

2) Concentration = a measure of thenumber of particles of matter per unitvolume

a) An increase in the concentration of thereactants generally increases reactionrate.

b) A decrease in the concentration of thereactants generally decreases reactionrate.

3. Temperature = a measure of the averagekinetic energy of the particles in a sampleof matter

a) An increase in temperature increasesreaction rate.

b) A decrease in temperature decreasesreaction rate.

4. Presence of a catalyst = a substance thatincreases the rate of a chemical reactionwithout being permanently changed

a) A catalyst will increase reaction rate.

b) A catalyst is not permanently changedin a chemical reaction.

1. Assumptions of collision theory:

a) Reacting molecules must collide witheach other.

b) Reacting molecules must collide withsufficient energy.

c) Reacting molecules must collide in anorientation that can lead torearrangement of the atoms.

2) Use collision theory to explain why anincrease in concentration increasesreaction rate:

a) ) At a higher concentration more reactantmolecules are present.

b) When more reactant molecules are presentmore frequent collisions occur.

c) When more frequent collisions occur thereare more chances for molecules to react (soreactions happen faster).

3. Use collision theory to explain why anincrease in temperature increases reactionrate:

a) Molecules with a higher kinetic energy movefaster, collide more often, and have moreenergetic collisions.

b) A higher temperature means that theaverage kinetic energy of the reactingmolecules is increased; at a highertemperature there are more molecules with ahigher kinetic energy.

c) At a higher temperature there are morefrequent collisions giving molecules morechances to react (so reactions happenfaster).

d) At a higher temperature, more moleculespossess enough kinetic energy to react soa higher percentage of collisions result inmolecules reacting (so reactions happenfaster).

•