Chemistry 11 – Notes on Chemical Reactions

2

Balancing Chemical Equations:

• A chemical equation is balanced if there is the same number of each type of atom on each side of the equation.

Example: (NH4)2S + Pb(NO3)2 ! NH4NO3 + PbS Guideline to balancing equations:

1. Put coefficient to balance (big numbers in front of each chemical)

2. Balance entire groups (eg. polyatomic ions: NO3-, NH4

+) first if they are

found on both sides.

3. Balance metal atoms next .

4. Try to avoid balancing H , and O ’s until the end if possible. These atoms

are often found several times throughout an equation.

5. If there are fractions in the equation (eg. ½ O2), multiply the equation by the

whole number (eg. 2) to eliminate the fraction.

6. Always double check your equation after balancing.

Answer: (NH4)2S + Pb(NO3)2 ! 2 NH4NO3 + PbS

Example #2: N2 + H2 ! NH3 Answer: Balance N first N2 + H2 ! 2NH3

Hydrogens in NH3 now have a coefficient in front of it, check on the other side of the equation for H’s and balance them too! N2 + 3H2 ! 2NH3 Subscripts:

• A chemical equation can also show the states in which the reactants and products

exist. The states of chemicals are shown by including the following

symbols in brackets immediately after the chemical formula.

(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous [“dissolved in water”]

Solid liquid gas aqueous

I I dissolved in H2O

11 PPT" "

powder"

"dissolved "

"

crystal "Solution

"

Chemistry 11 – Notes on Chemical Reactions

3

Example: Solid zinc reacts with a hydrochloric acid solution to form hydrogen gas and dissolved zinc chloride. Zn (s) + 2HCl (aq) ! H2 (g) + ZnCl2 (aq)

• Note: “crystals”, “powder”, and “precipitate” all mean the phase is a solid ! Defn:

• Precipitate: a solid formed when two liquid or aqueous solutions react. Predicting Products

• The key to predicting products is to be able to identify the type of reaction that the reactants will undergo

Example:

1. NO2 ! ?

• There is only one compound on the reactant side. This is a decompose

tion reaction!

• The compound will break down into its individual elements.

Therefore: 2NO2 ! N2 + 2O2

2. Mg + ZnSO4 ! ?

• There is one element and one compound on the reactant side. This is a

single replacement reaction!

• The metals (or non-metals) will switch places. Therefore: Mg + ZnSO4 ! Zn + MgSO4

3. Al + O2 ! ?

• There are two elements by themselves on the reactant side. This is a

synthesis reaction!

• The elements combine to form one compound.

Therefore: 4Al + 3O2 ! 2Al2O3

¢Always Cag )

↳ Translate E include States

Enes ,t 2 HCl cap

→ Hug , t In Clzcaq,

solid substance that forms by mixing multiple

Solms .

identify chemical rxn

Dbreak Into smaller pieces .

2 NO 2 it Nz +202

SR

→Mg t ZnS04 En + Mgs Ot

S

one compound

4 At +302 → 2 At 203

Chemistry 11 – Notes on Chemical Reactions

4

4. HCl + KOH ! ?

• There is an acid and a base on the reactant side. This is a neutralization

reaction (a special case of double displacement reaction)!

• Water is one product, and the other ions combine to form a salt.

Therefore: HCl + KOH ! KCl + H2O

5. C2H2 + O2 ! ?

• There is a hydrocarbon compound and oxygen on the reactant side. This

is a combustion reaction!

• The products will be CO2 and H2O

Therefore: 2C2H2 + 5O2 ! 4CO2 + 2H2O

ACID BASE

N

DR

salt

HCl t KOH → H2O t Kel

c

CO2 t H2O

" CHO"

2 even 4 2

XC2H2 t 502 → * CO2 t XHZO✓ Odd

4 t I = 5

evene) XZ

8 t 2 = 10

Home Fun

④ ass : Finish marking HI # 8

marking } QUE next

Finish HI # 9 class !

@ Home Finish pre lab 5C

Chemistry 11 – Notes on Chemical Reactions

5

Type of Reaction Definition General Formula Examples What to look for!

Synthesis (S) Combination of two or more

substances to form a compound

A + B ! AB

C + O2 ! CO2

H2 + Cl2 ! 2HCl

Two elements as reactants.

Decomposition (D) Breaking down a molecule into simpler substances AB ! A + B

2KClO3 ! 2KCl + 3O2

2Ag2O ! 4Ag + O2

One compound as a reactant.

Single Replacement (SR)

Replacing one atom in a compound by another atom AX + B ! BX + A

Cu + 2AgNO3 ! Cu(NO3) 2 + 2Ag

Cl2 + 2KI ! I2 + 2KCl

Element and a compound react.

Double Replacement (DR)

Exchange of atoms or groups between two different

compounds AX + BY ! AY + BX Pb(NO3) 2 + 2KI ! PbI2 + 2KNO3

Two compounds react.

Neutralization (N) Special type of double

replacement. Reaction of an acid with a base

HA + BOH ! H2O + BA H2SO4 + 2KOH ! K2SO4 + 2H2O

HCl + NaOH ! NaCl + H2O

Acid (starts with “H”) and Base (end with

“OH”) react

Combustion (C) Reaction of hydrocarbon with

oxygen to produce carbon dioxide and water

CxHy + O2 ! H2O + CO2 CH4 + 2O2 ! CO2 + 2H2O

C5H12 + 8O2 ! 5CO2 + 6H2O

Hydrocarbon and O2

¥I

onO

§s

&S

Tp

No

µN

-gon§

os

44

Eu

7Ile

ITs

s#

So

If

Oa

Ts

uI

Ao

Eo

8-

Eto

og

s-

sg

tf

e¥

Iat

oEF

A

EEgeese

8+

tat

we

E88

sg

1-s

I-

oa

ts

soI

oo

sB

toof

Eto

EsI

Oa

EA

aE

toI

=-

T

ZJoe

I£

Ee

8To

tme

8If

0A

In

-or

fI

sE)

aI

Ot

n-

Xo

D-

ororg

td

I+

uE

-8

t^

ITit

t=

au

t^

D8

7-

§5

orI

*t

¥8I

N8

O-

tf

-or

ao

Is

ofe

IFof

te

eor

Eor

in°

fIif

asIf

'fo

in+

oor

onef

-E

Ht

-n

t8

do=

er

•T

orIs

Vas

SOI

I$

STD

NI

les

soA

ISoo=

aF-

OF

AwI

EI

Gi

&t

*I

tI

-

p*

*fttEH

'sIse

T+

Stein0

o-

+

WX

a④

OT

t0

m-m

esor

+gogtf

tt

I⇒

InI

1-X

yE

a*

ugoals

$I

-o

sE

Es

aN-

eI

ef

Sin

ECs

EE

Io

EEs

8A

8II

IFI

UEA

•E

II

z5

WB

8BE

EEE

ECs

aE

Iu

oE

aa

zO