Sect.11-1 “Chemical Reactions”Chemical Rn: __________________________

___________________________________ ___________________________________

Reminder:Substances before reaction = ___________Substances after reaction = ___________

Signs that a chemical rn has occurred:

1.) _________: Does rn produce or absorb heat?

2.) ________: Does rn produce light?Note: Heat/Light is not proof

positive that a rn has occurred.3.) _____________: Bubbles form in the

rn.4.) _______________: when 2 liquid

solns are combined and a solid is produced – solid is known as a ___________.

Characteristics of a Chemical Eqn.

1.) Eqn needs to _______________________.

2.) Need _________________ for reactants and products.

3.) Law of Conservation of Mass holds. i.e. total mass before = total

mass after or more importantly:

_________________________________

Word Eqns

It’s easier to write an eqn by first writing it in words – __________.

It is qualitative because no numbers are used.

e.g. __________ + _________ → _________

__________ + Hydrogen → __________

where“+” means “reacts with” and is read

as “and”“→” means “yields” or “produces” and

is read as such.

Next step:Convert the words into formulas, called a “Formula Equation”

e.g. Hydrogen + Oxygen → Water ___ + ____ → ____

Nitrogen + Hydrogen → Ammonia___ + ____ → _____

(examples of formulas vs symbols?)Elemental Gases – F2, Cl2,… Liquids – Br2,

Solid Metals – Na, Mg, Ca…Solid Non-Metals – S8, P4, I2.

Last step: Balance the equation to create a “Balanced chemical equation”i.e. the # of each type of element

before = aftere.g. Hydrogen + Oxygen → Water

H2 + O2 → H2O2 H atoms 2 H

atoms 2 O atoms 1 O atom

Therefore need to balance.e.g. Nitrogen + Hydrogen → Ammonia

N2 + H2 → NH32 N atoms + 2 H atoms ≠ 1 N atom and

3 H atomsTherefore need to balance.

Trick: _______________________________ _______________________________.

e.g.1:H2 + O2 → H2O (H is OK, now look at O)H2 + O2 → 2H2O (O is fixed, but H is now

unbalanced. (Cannot fix H2O by changing it to H2O2

because you are changing the actual formula. Coefficient multiplies everything after it.)

2H2 + O2 → 2H2O (H and O are now balanced)

i.e. # H before (4) = # H after (4) # O before (2) = # O after (2)

e.g.2N2 + H2 → NH3 (balance the N)N2 + H2 → 2NH3 (now, balance the H)N2 + 3H2 → 2NH3 (double check)# N atoms (2) before = # N atoms (2)

after# H atoms (6) before = # H atoms (6)

afterBalanced Example: CH4 + O2 → CO2 + H2O

Example: C3H8 + O2 → CO2 + H2O

(other examples)BaCl2 + AlN Ba3N2 +

AlCl3

Balancing tricks / hints:1) Balance the elements one at a time2) First balance the atoms of the elements that

are combined and that only appear once on each side of the equation

3) Treat polyatomic ions that appear on both sides of the equation, as single unitse.g.

_Al2(SO4)3 + _Ca(OH)2 → _Al(OH)3 + _CaSO4

4) Balance the H & O atoms last5) If you have a Hydroxide (OH) on one side, and

water (H2O) on the other side, then treat H2O as H(OH).e.g. Ca + H2O Ca(OH)2 + H2

Other symbols used in Chemical equations:

(s) solid e.g. NaCl(s) (t) liquid e.g. H2O(l) (u) gas e.g. CH4(g) (aq) aqueous – dissolved in water e.g. NaCl(aq)

precipitate (solid) is formed e.g. AgCl(s)

gas is formed (bubbles) e.g. H2(g)

heat used/required catalystreversible reaction (or )

(do examples with above symbols)H2O2(aq) H2(g) + O2(g)

∆

KMnO4

KMnO4

Magnesium metal is placed into a solution of Iron (III) Chloride to produce solid Iron and Magnesium Chloride solution.

Word Eqn:.

Formula Eqn:

(Balanced) Chemical Eqn:

Ethane (C2H6) gas burns in air to produce Carbon Dioxide gas and water vapor.

Word Eqn:

Formula Eqn:

(Balanced) Chemical Eqn:

Types of Reactions:1) Synthesis Rn: (aka Composition

rns)- aka direct combination rn.Where ____________________ to form a

new compound. Generalized by:__________________

e.g. 2H2(g) + O2(g) → 2H2O(g)

e.g. Mg(s) + Cl2(g) → MgCl2(s)Most metals react with O & S to

produce Oxides & Sulphides.e.g. 2Mg(s) + O2(g) →

2MgO(s)e.g. 8Ba(s) + S8(s) → 8BaS(s)

Non Metals react with Oxygen to produce Oxides

e.g. S8(s) + 8O2(g) → 8SO2(g) Sulphur DiOxide

e.g. C(s) + O2(g) → CO2(g) Carbon DiOxide

e.g. 2H2(g) + O2(g) → 2H2O(g) Hydrogen Oxide(?)

Active metal oxides react with H2O to produce metal hydroxides.

e.g. Na2O(s) + H2O(l) → 2NaOH(s) or (aq)?

2) DeComposition Reactions:-a ______________________ (breaks down)

into 2 or more simpler substances. Usually requires an input of Energy. (Heat, electricity..)

Generalized by:__________________

e.g. 2H2O(l) electricity 2H2(g) + O2(g) (Electrolysis)

e.g. 2HgO(s) ∆ or Heat 2Hg(l) + O2(g)

e.g. H2O2(l) KMnO4 H2(g) + O2(g)

3) Single Replacement reactions:- where ___________________________ ____________________: Generalized by:

A + BX → AX + Bm m nm m nm m

OrY + BX → BY + Xnm m nm m nm nm

Rns usually need to take place _____________

Examples:Mg(s) + AgNO3(aq) →

Cl2(g) + NaBr(aq) →Note: Just because you can write a chemical

rn, it doesn’t mean that it will happen.We need to consult the __________________- a list of elements organized according to how

reactive they are. (see p.333 & handout)_______________________________________________

____________________________________________________________________________

Same goes if Y is higher than X on the list.( Do examples )

4) Double Replacement Rns:- where _______________________________

_____________________________. Generalized by:

AX(aq) + BY(aq) → AY + BXm nm m nm m nm m nm

In order for a double replacement rn to occur, one of the products must be a:

a) ______________ (solid), orb) _________, orc) _______ [remember: H+ + OH- → HOH

(H2O)]

If products do not contain one of the previous 3, then rn will not occur.

Examples: Precipitate: (need to look at

Appendix:B, Table B-9 on p.R54)KI(aq) + Pb(NO3)2(aq) →

Gas:FeS(s) + HCl(aq) →

Water:HCl(aq) + NaOH(aq) →

5.) Combustion Rns:- Is when a ______________________ (in the air) releasing a large amount of energy in the form of light, heat and sometimes sound.

*If the substance is a HydroCarbon (CXHY) or an Alcohol (CXHY-1OH) then _______________ ________________ which we will focus on mostly.

e.g.C2H6(g) + O2(g) →Ethane

C2H5OH(l) + O2(g) →Ethanol