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Chapter 9 Part 1 : Types of

Chemical Reactions

5 common

Reaction types:

Reaction Types 1. Composition reactions

a.k.a. synthesis or

combination reactions

•A + B AB

Composition (Synthesis)

Reactions

composition Examples:

2H2 (g) + O2 (g) 2H2O (l)

CaO(s) + H2O(l) Ca(OH)2(aq)

2. Single Replacement

Reactions

• Metal replaces another metal

• C + AB A + CB

Or…

• nonmetal replaces another

nonmetal

• C + AB B + AC

Single-Replacement Reactions

• SR Examples:

Pb + 2HNO3 Pb(NO3)2 + H2

F2 + 2NaI 2NaF + I2

Predict the Products

Zn + CuCl2 ZnCl2 + Cu

3. Decomposition reactions

•When compounds split

up (break down) into 2

or more products

• AB A + B

Decomposition Reactions

Decomp Examples

• CaCO3 CaO + CO2 (g)

• Na2CO3 Na2O + CO2 (g)

4. Double Replacement

Reactions

• AB + CD AD + CB

The ions of two compounds exchange places in an aqueous solution to form two new compounds.

Two ionic compounds “swap” ions.

Double Replacement

Reactions

Usually forms a precipitate

• precipitate: a solid product that is formed when two aqueous solutions are mixed.

AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)

Precipitate

Examples

PbSO4(aq)+2KCl(aq) K2SO4(aq) + PbCl2 (s)

AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)

Predict the Products

H2O

KOH + H2SO4 K2SO4 + HOH

5. Combustion reactions

• CXHY + O2 CO2 + H2O

• Easily recognized when O2 is

one reactant, and CO2 & H2O

are the products

Example

• C3H8 + 5O2 3CO2 + 4H2O

• CH4 + O2 CO2 + H2O

Practice time!!!!!

1) 2Li + 2H2O 2LiOH + H2

single replacement / displacement

2) NH4Cl NH3 + HCl

decomposition

3) AgNO3 + NaCl AgCl + NaNO3

double replacement / displacement

4) 2C6H14 + 19O2 12CO2 + 14H2O

combustion

5) N2 + 3 H2 2 NH3 Composition/synthesis

Chemical Reaction • a change in which one or more substances are converted into new substances – · old bonds break

– · new bonds form

– · atoms are rearranged

Indicators of reactions:

1.Production of heat and/or light.

2.Production of a gas: bubbles in a solution

3.Formation of a precipitate (solid)

4.Color change

Chemical Equation • a way to describe a chemical reaction using chemical formulas and other symbols

• Reactants Products

• (starting material) (new substances)

Common Symbols used in Equations

= yields, forms, produces, makes, etc

(s) solid state or precipitate

(l) liquid state

(g) gaseous state

(aq) aqueous state (dissolved in water)

: heat is applied (placed over the arrow)

catalyst (also written over the arrow)

substance that speeds up a chemical reaction without becoming part of the reaction.

Diatomic molecules

• 7 diatomic elements (know) H2 O2 F2 Br2 I2 N2 Cl2 - “infamous 7” or “HOFBrINCl”

(If any of these are present in a reaction as a reactant or product they must be shown as diatomic)

Unit 3 – part 1 • balancing equations (eqn)

Significance of Equations

• Coefficients show relative amounts of reactants and products in the equation

• When an equation is balanced it will satisfy the law of conservation of mass

Law of conservation of mass states that:

• Atoms are neither created nor destroyed (in ordinary chemical reactions). – number of atoms on left = number of atoms on right

– In balancing, do not split up compounds or change the formula (subscripts).

– Remember common polyatomic ions and diatomic molecules.

Subscripts vs. Coefficients

• Subscripts tell how many

atoms of an element are in

the compound.

• SUBSCRIPTS CAN NEVER

BE CHANGED!!!!!!!!

• Coefficients are found at the

beginning of a formula, and

indicate the number of moles

present in the equation.

• If no coefficient is written it is one

• Coefficients CAN BE changed in

balancing equations.

Order for Balancing

(recommend making a chart

under the arrow)

1.M - metals (Balance metals first.)

2.I - ions (Balance polyatomic ions.)

3.N – nonmetals (Balance Cl, S, N, etc.)

4.O – oxygen

5.H – hydrogen

To balance combustion Rxn:

CHO (carbon then hydrogen

and oxygen last)

When there are an odd

number of oxygens in the

products, do the “half-trick”

Two Important Principles!!!

• Every chemical compound has a

formula that cannot be altered

(can’t change the subscripts).

• A chemical reaction must account

for every atom used. (Law of

Conservation of Mass)

THE END