Chemical reactionstypes and balancing

2/14/11 – “C” dayObjective: To assess the concepts of ionic and covalent bonding.

Do Now: What property of water is determined by its shape? How do water molecules behave?

2/15/11 – “D” dayObjective: Introduce the concept of chemical reactions.

Do Now: Balance the following: P4 + O2 P4O6

Today:1. Check in HW2. Check Answers 3. More Balancing

Equations

2/16/11 – “E” dayObjective: To apply law of conservation of mass to chemical reactions.

Do Now: What is the law of conservation of mass? Today:

1. Collect 11.1 Guided Read

2. Chemical Reaction Notes

3. Reaction in a Bag Lab

Chemical reactions

When one or more reactants are changed into one or more products, a chemical reaction has occurred.

The atoms do not change, but are rearranged.

Chemical reactions

The changing of substances into other substances by the breaking of old bonds and the formation of new bonds

Terms to remember

The number in front of a substance is called the coefficient

The coefficient multiplies everything in the substance

Terms to remember

Subscript – the number under an element – for example the 2 in O2

The subscript tells how many of that type of atom is in a compound

Practice

How many of each type of atom are there in 2 Al2(SO4)3?

4 Al

6S

24 O

Chemical reaction- example

Adding HCl to Zn

http://www.youtube.com/watch?v=HxiW2iPUZiw&feature=related

How many safety mistakes can you find?

Mistakes

Goggles?

Gloves? – Really strong HCl

Poor judgment – comment about holding balloon in teeth

Fire/explosion

Zn + HCl

What happened?

How can you tell that a chemical reaction occurred?

Chemical reaction

HCl + Zn → ZnCl2 + H2

The atoms in the products are the same atoms that

were in the reactants, they are just

arranged differently.

Nomenclature

HCl + Zn → ZnCl2 + H2

Reactants → Products

Reactants react to produce products

LAW OF CONSERVATION OF

MATTERnumber and type number and type

→ READ as an = sign

HCl + Zn → ZnCl2 + H2

Are there the same number of atoms of each type on each side of the →?

Balancing equations

HCl + Zn → ZnCl2 + H2

Step 1: Count the number of each type of atom on each side

H

Cl

Zn

Balancing equations

HCl + Zn → ZnCl2 + H2

Step 2: compare numbers, what needs to be changed to make them the same

H 1 → 2

Cl 1 → 2

Zn 1 → 1

Balancing equations

2HCl + Zn → ZnCl2 + H2

Step 3: compare numbers, is it balanced now?

H 2 → 2

Cl 2 → 2

Zn 1 → 1

Chemical Reaction 2

H2 + O2 → H2O

Is this balanced?

How would you balance it?

Chemical Reaction 2

2H2 + O2 → 2H2O

Diatomic molecules

7 elements, most of which we will use all the time, exist in nature as diatomic molecules, which means they only exist as a molecule of 2 atoms bonded together

Diatomic molecules

H2, N2, O2, F2, Cl2, Br2 and I2

Notice that all but H2 form a 7 on the periodic table.

You need to know these.

Practice balancing equations

Worksheets

Types of reactions

Chemical reactions can be classified into 5 different types:

Synthesis Decomposition Single replacement Double replacement Combustion

Synthesis reactions

Reactants: either 2 elements OR 2 compounds

Product: MUST be a compound

USUALLY combination is

2 reactants 1 product

A + B → AB

Synthesis reactions

Examples

N2 + 3H2 2NH3

2H2 + O2 2H2O

Decomposition

The opposite of synthesis

One reactant making 2 or more products

AB → A + B

2KClO3 2KCl + 3O2

2Ag2O 4Ag + O2

Single Replacementone atom takes the place of another atom

in a compound

A + BC B + AC

A has replaced B in this reaction

Single Replacement

Examples 2NaCl + F2 2NaF + Cl2

Na + H2O NaOH + H2

K + MgBr2 KBr + Mg

Double Replacement

When (usually) ions in 2 compounds switch places to form 2 new compounds.

AB + CD → AD + BC

Remember, positive charge (metal) is always written first

Examples

CaCl2 + Na2SO4 → CaSO4 + 2 NaCl

FeCl2 + K2S FeS + 2KCl

Combustion

Reactants: Carbon and Hydrogen containing compound reacting with oxygen

Product: Carbon dioxide and water

CxHy + O2 CO2 + H2O

Combustion

Examples

CH4 +3O2 → CO2 + 2 H2O

C3H8 + 5O2 3CO2 + 4H2O

Types of reactions

Demonstration Lab

Types of reactions

Types of chemical reactions IF WS

Synthesis – Predicting products

and balancingTwo or more reactants one

product

Examples:

Na + Cl2

2Na + Cl2 2NaCl

Synthesis – Predicting products

and balancingRb + Cl2

Rb + Cl2 RbCl

2Rb + Cl2 2RbCl

K + Cl2

K + Cl2 KCl not balanced

2K + Cl2 2KCl

Decomposition

one reactant two or more products

Exact opposite of a synthesis reaction

Decomposition

Seltzer water (carbonic acid) decomposes to produce carbon

dioxide and water:

H2CO3 CO2 + H2O

Decomposition: one reactant, two (or more products)

Decomposition

Decomposition

Often decomposition requires adding energy.

If you add electricity to water, can make it decompose:

H2O → H2 + O2

2H2O → 2H2 + O2

Balancing Synthesis and Decomposition Reactions WS

Single replacement reactions

A + BC → B +AC

Two metals and one nonmetal

OR

AB + C →AC + B

Two nonmetals and one metal

Single replacement

Single Replacement

Examples of two metals and one nonmetal

Al + CuCl2 AlCl3 + Cu

Balance:

2Al + 3CuCl2 2AlCl3 + 3Cu

Single Replacement

Examples of two nonmetals and one metal

Mg + HCl MgCl2 + H2

Balance

Mg + 2HCl MgCl2 + H2

Try these SR reactions

Use the following steps:

Identify which reactants are switching places

Determine neutral ratio for new compound

Draw reaction arrow and complete reaction

1.MgBr2 and Cl2

2. KI and F2

Answers

1. Magnesium Bromide and ChlorineMgBr2 + Cl2 . Bromine and Chlorine==> MgCl2 + Br2

2. Potassium Iodide and Fluorine 2KI + F2 Iodine and Fluorine ==> 2KF + I2

Balancing SR reactions WS

SR reactions Lab

Double Replacement

AB + CD → AD + BC

Involves the exchange of positive cations

Gas, precipitate or water is produced

DR - remember

positive ions are always written first when listing the product

METALS are positive ions and NON-METALS are negative ions

a positive must join with a negative

Double Replacement

Double replacement reactions usually involve 2 solutions that when mixed give a precipitate (solid). Example:

KBr + AgNO3

KBr + AgNO3 AgBr(s) + KNO3 balanced

Ppt formed

Double replacement – acid and base

A special kind of double replacement reaction is when an acid (H) is mixed with a base (OH). Example:

HNO3 + LiOH

HNO3 + LiOH LiNO3 + H2O balanced

Water formed

Double Replacement

How to predict products:

ID cations

Switch them!

Write proper formulas

Balance

Double replacement lab

Balancing DR WS

Putting it all together: Predicting Products and

Balancing• Determine the type of reaction:

synthesis, decomposition, s/d replacement, or combustion

• Make sure elements present on left are present on right

• Make sure all charges are net zero

• Balance equation.

Will the reaction occur?

Will a metal replace another in a single replacement reaction?

Table called an activity series ranks metals from most active to least active.

Will the reaction occur?

More active metals will form compounds.

A + BC → B + AC

Reaction occurs only if A is more reactive than B

What do you notice about these metals?

Why do you think jewelry is made using copper, silver, gold and platinum?

Activity of metals lab

Will the reaction occur?

In double replacement reactions, the reaction will occur if one of the products forms a precipitate, a gas or water.