Chemistry - Chemical Reactions
-
Upload
alexander-gan-zhong-ping -
Category
Education
-
view
1.688 -
download
0
description
Transcript of Chemistry - Chemical Reactions
This presentation was produced by the Science department of Temasek Secondary School. Redistribution or reproduction of this resource is prohibited by copyright regulations.
Other Chemical Reactions
OTHER CHEMICAL REACTIONS
You will learn:
• Combination reaction
• Combustion reaction
• Thermal decomposition
OTHER CHEMICAL REACTIONS
Elements can react in many ways to form new compounds.
The new compound formed will have totally different properties from the starting elements.
Two elements can react to form a new compound in a combination reaction.
Example 1:
Two elements can react to form a new compound in a combination reaction.
Example 1:
elementelement
sodium(soft silvery
metal)
sodium(soft silvery
metal)
elementelement
chlorine(greenish-yellow poisonous gas)
chlorine(greenish-yellow poisonous gas)
compoundcompound
sodium chloride /
common salt(white solid)
sodium chloride /
common salt(white solid)
Combination Reaction
Example 2Example 2
Formation of copper chlorideFormation of copper chloride
elementelement
copper(reddish-brown
solid)
copper(reddish-brown
solid)
elementelement
chlorine(greenish-
yellow poisonous gas)
chlorine(greenish-
yellow poisonous gas)
compoundcompound
copper chloride(green solid)
copper chloride(green solid)
Combustion Reaction
-When an element burns in oxygen
Example 1:Burning of magnesium strip
magnesium + oxygen magnesium oxide
magnesium
Combustion ReactionExample 2
hydrogen + oxygen water
Video: http://www.youtube.com/watch?v=k5MJhuaXUlc&feature=related
http://www.youtube.com/watch?v=e6ejjNsJegk&feature=related
H2 O2
Breaking up a Compound by Heating-Thermal DecompositionBreaking up a Compound by Heating-Thermal Decomposition
A compound may be broken down into simpler substances. Heating is needed.A compound may be broken down into simpler substances. Heating is needed.
New compound 1New compound 1
Copper oxide
(black powdery solid)
Copper oxide
(black powdery solid)
New compound 2New compound 2
Carbon dioxide
( colourless gas)
Carbon dioxide
( colourless gas)
Starting compound
Starting compound
copper carbonate
(green powder)
copper carbonate
(green powder)
Video: http://www.youtube.com/watch?v=FYUWY39ikcI&feature=related
WRITING CHEMICAL EQUATIONS
Writing Chemical Equations
You need to know:1. The correct chemical formula of elements (metals e.g Na. Zn, Al, Mg etc)
(gases: e.g Cl2, H2, O2 etc)
2. Chemical formula of compounds (based on your knowledge of valency)
Example: chemical formula of
magnesium chloride: Mg Cl2
Writing Chemical Equations
3. Balancing the equation
This is to ensure that the no of atoms of each elements is the same before and after the reaction.
Example : Reaction of hydrogen and chlorine gas
Is this chemical equation balanced?
H2 + Cl2 2 HCl
H H ClCl Cl
H
ClH
Balancing Chemical Equations
• All chemical equations must be balanced.
• The number of atoms of an element before and after the reaction must be the same as the Law of conservation of Matter states that:
Atoms cannot be created nor destroyed in a chemical reaction.
How to Balance?
H2 + Cl2 HCl
Left hand side Right hand side
2H atoms 2 Cl atoms 1H atom and 1 Cl atom
This equation is not balanced.
How to Balance?Balancing can be achieved by changing the
number in front of the formula
H2 + Cl2 HCl
Left hand side Right hand side
2H atoms 2 Cl atoms 1H atom and 1 Cl atom
H2 + Cl2 2 HCl
Left hand side Right hand side
2H atoms 2 Cl atoms 2H atoms and 2 Cl atoms
Balanced!
More Examples
Writing Chemical Equations
Combination ReactionExample 1
Sodium + chlorine sodium chloride
Step 1: Write the chemical formula
Na + Cl2 NaCl
Step 2
Balancing to ensure atoms of each elements are the same on both side.
Why the need to balance chemical Equations?Law of Conservation of Matter:
Atoms cannot be created nor destroyed
Step 2: Balancing
Na + Cl2 NaCl
2 NaCl
2 2 NaCl
First try not balanced
Second tryBalanced!
Na + Cl2
Na + Cl2
Combination ReactionExample 2
Copper + chlorine copper (II) chloride
Step 1: Write the chemical formula
Cu + Cl2 CuCl2
Step 2 :Balancing to ensure atoms of each elements are the same on both side
Cu + Cl2 CuCl2
No need to balance
Combustion ReactionExample 1
Magnesium + oxygen magnesium oxide
Step 1: Write the chemical formula
Mg + O2 MgO
Step 2 :Balancing to ensure atoms of each elements are the same on both side
Need to balance?
Mg + O2 MgO22
Combustion ReactionExample 2
Hydrogen + oxygen water
Step 2 :Balancing to ensure atoms of each elements are the same on both side
Step 1: Write the chemical formula
H2 + O2 H2O
Need to balance?
H2 + O2 H2O22
Thermal Decomposition ReactionExample 1
Copper copper + carbon
Carbonate oxide dioxide
Step 2 :Balancing to ensure atoms of each elements are the same on both side
Step 1: Write the chemical formula
Cu CO3 CuO + CO2
Need to balance?
It is already balanced
Summary
• A chemical reaction can be represented by a word or chemical equation.
• Word equations can be converted into a chemical equations by using chemical formulas.
• All chemical equations must be balanced.
Part II
Chemical Equations for
Reactions of Acids
Reactions of Acids
Complete the worksheet given on writing words and chemical equations
Note:
You must know the
*chemical formula of acids and alkalis
* chemical formula of the salts