chemistry - chemical reactions
DESCRIPTION
This presentation was designed to meet the GCE 'O' Level Chemistry syllabus. The presentation will discuss on Combination, Combustion and Thermal Decomposition Reactions.TRANSCRIPT
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This presentation was produced by the Science department of Temasek Secondary School. Redistribution or reproduction of this resource is prohibited by copyright regulations.
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Other Chemical Reactions
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OTHER CHEMICAL REACTIONS
You will learn:
• Combination reaction
• Combustion reaction
• Thermal decomposition
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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.
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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
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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)
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Combustion Reaction
-When an element burns in oxygen
Example 1:Burning of magnesium strip
magnesium + oxygen magnesium oxide
magnesium
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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
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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
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WRITING CHEMICAL EQUATIONS
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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
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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
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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.
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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.
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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!
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More Examples
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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.
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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
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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
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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
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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
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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
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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.
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Part II
Chemical Equations for
Reactions of Acids
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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