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```Science 1st prep. 2nd term, unit 1 lesson 3
Chemical equation & Chemical reaction
Chemical Reaction
Chemical Reaction are used as electrical and heat energy resources.
Most of the modern industries depend mainly on the chemical reactions such as, manufacture
of (fertilizers, car batteries, fuel, plastics, food industries, ………. etc)
What’s meant by chemical reaction?
Conclusion
Magnesium
reacts with
atmospheric
oxygen
(reactants)
to from a
new
substance which is magnesium oxide
(product).
2Mg + O2
2MgO
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Observation
The solid magnesium ribbon
with a glowing light and
changes from a bendable
bright solid into a white
power of a new substance.
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Steps
Hold a piece of
magnesium ribbon by
a test tube holder.
Burn the ribbon in
the air.
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To understand the concept of chemical reaction, we carry out the following activity : -
Explanation of Reaction:
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r.A
1 - Heat energy has broken the double covalent bond in oxygen molecule (O2) to give two
active oxygen atoms.
2- Oxygen atom joins with magnesium atom to from a molecule of manganese oxide by an ionic
bond.
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Science 1st prep. 2nd term, unit 1 lesson 3
Chemical reaction
It is a process that involves breaking the existing bonds in the reactant molecules and
forms new bonds in the products.
Chemical Equation
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A Chemical reaction can be represented by “Chemical Equation”
Reactants
reaction conditions
products
Chemical Equation
It is a set of symbols and chemical formule representing the reactants and products
molecules in the chemical reaction and it represents the conditions of the reaction if they
exist.
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The chemical equation must be balanced such that the number of atoms entering a reaction equals
Examples:
2Mg + O2
C + O2
2MgO
heat
CO2
r.A
heat
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the number of atoms resulting from this reaction.
Law of constant ratios
Activity 2 to verify the law of constant ratios:
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Given that the atomic mass of Mg = 24 and that of oxygen = 1 6, we can calculate the total
mass of reactants and products in the following equation.
2Mg +
O2
(2 x 24) + (2 x 16)
48 +
32
80
2MgO
= 2 (24+16)
= 2 x 40
= 80
Observation
Each 48 g of magnesium joins with 32 g of oxygen to form 80 g of magnesium oxide.
i. e. the mass of the reactants = the mass of the products = 80 gm.
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Science 1st prep. 2nd term, unit 1 lesson 3
Conclusion:
A compound is produced from a chemical combination of atom of two elements or more by
constant weight proportions.
So, we can conclude the law of constant ratios as follows:
Law of constant ratios
The total amount of reactants masses is equal to the total amount of products masses.
G.R. the chemical equation should be balanced?
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Because the total mass of the reactants before the reaction must be equal to the
total mass of the products after the reaction.
Types of chemical reactions
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Compound
&
Compound
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Element
&
Element
A : combination of element and another one.
+
Non metal
S
+
O2
non metal
CO2
carbon dioxide
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C
r.A
1 - Combination between two non metals
SO2
sulphur dioxide
O2
non metal
Non metal
Combination between metal and non metal
Mg
+
Metal
2Na
Metal
+
O2
non metal
magnesium oxide
2MgO
Cl2
non metal
sodium oxide
2NaCl
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Element
&
Compound
Science 1st prep. 2nd term, unit 1 lesson 3
B. A compound and a compound
Example : combination of ammonia gas and hydrochloric acid.
+
HCl
Compound
NH4Cl
Compound
Ammonium chloride (white fumes)
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NH3
C : combination of element with compound
Example 1
Reaction of oxygen with carbon monoxide (CO)
+
O2
→
2 CO2
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2 CO
Example 2
+
O2
→
2 NO2
r.A
2 NO
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Reaction of nitrogen monoxide and oxygen
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Chemical reaction in our life
Some chemical reactions play a vital role in our life and others have negative impacts
(effects) on both human beings and environment.
A Useful applications of chemical reactions
Through chemical reactions, thousands of compounds are commonly used in many industries
such as medicines, fertilizers, fuel, plastics and others.
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Science 1st prep. 2nd term, unit 1 lesson 3
B Negative effects of chemical reactions on human beings and environment:
1 - Fuel burning
It is an example of environment pollution due to the presence of
harmful gases such as carbon oxides {carbon dioxide (CO2) and
carbon monoxide (CO) which increase the air temperature,
where:
Carbon dioxide (CO2) acts as a greenhouse as it permits the penetration of rays from the sun
to the earth and never let them return back.
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Carbon monoxide (CO) has a dangerous impact on the human being which it causes:
2 - Sulphur Oxides ( SO2 , SO3 )
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They are acidic gases causing:
Respiratory system malfunction (breathing problems). and Building
corrosion.
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3 - Nitrogen Oxides ( NO , NO2 )
They are acidic gases that are resulted at the time of lighting.
They are poisonous and that affect the nervous system and the eye.
4 - Burning of coal and cellulose fibers
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Such as burning paper and cigarettes cause air pollution and lung cancer.
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Questions on lesson:
Complete the following statements:
1 – the chemical equation is a set of ……………………………. And ………………………. . expressing the
reactants and …………………………………. In the chemical reaction.
2- the chemical reaction is the process in which bonds existing in the reactants are
………………………………………. . and forming new bonds in the ………………………………………. .
3 – if 48 gm of magnesium combine with 32 gms, of oxygen, they produce ………. . gm of……. . . .
4 –the chemical equation should be ………………………. . such that the total mass of the reactants
entering a reaction ………………………. The total mass of the products resulting from this reaction.
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Science 1st prep. 2nd term, unit 1 lesson 3
5 – compound is produced from a chemical combination of atoms of two elements or more by
constant weight proportions and this is known as law of ……………………………….
6 – when a glass rod wet with ammonia solution is put at the mouth of a test tube containing
concentrated hydrochloric acid, …………………………… fumes of ……………………… are formed.
7 – when carbon (fuel) is burned in air, it gives ……………………………………. .
8 – chemical reactions are used in many industries such as …………………………… and ……………………….
9 – carbon monoxide is a dangerous gas which causes ………………………. , ………………………and ………………
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1 0 – Nitrogen oxide are acidic gases that affect the ………………………. System and ……………………. .
1 1 – burning of coal and cellulose fibers causes ……………………. . pollution and …………………………
1 2 – carbon dioxide acts as ………………………………… as it permits the penetration of ………………….
Rays to the earth and never let them return back.
+ O2 → ………………………
2 – NH3
+ HCL
3 – 2 NO
+ O2
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1 – 2 Mg
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Complete the following eauation and mention the type of reaction?
→ ………………………. .
→ ……………………………….
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1 – the bright magnesium ribbon changes into white powder of ……………. When it burns in air.
a. magnesium nitrite
b. magnesium oxide
c. magnesium hydroxide
d. magnesium dioxide.
2 – if the molecule of carbon dioxide consists of one atom of carbon and two atoms of
oxygen, knowing that the mass of carbon is 1 2 and that of oxygen is 1 6 , so the mass of two
molecule of carbon dioxide equals …………………………. .
a. 22
b. 44
c. 88
d. 33
3 - direct combination reactions takes place between ……………………………
a. two nonmetals
b. a metal and a nonmetal
c. compound with another
4 – Ammonia combines with conc. HCL producing ………………………. . of ammonium chloride.
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Science 1st prep. 2nd term, unit 1 lesson 3
a. white ppt.
b. brown fumes
c. white fumes
d. brown ppt.
5 – chemical reaction are used in ………………………….
a. medicines industry
b. fertilizers industry
c. food industry
6 – if 58. 5 grams of NaCl solution react with 1 70 grams of AgNO3 solution to produce 85
grams of NaNO3 solution and AgCl, so the mass of AgCl will be ………………. . grams.
a. 1 43. 5
b. 287
c. 77. 5
d. 1 20
7 – the gas which is responsible for the greenhouse effect is …………………. Gas
a. carbon monoxide
b. carbon dioxide
c. nitric oxide
d. sulphur dioxide
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8 – the gases that affect the nervous system and the eye are ………………….
a. nitrogen oxides
b. carbon oxides
c. sulpher oxides
d. a and b
9 – all these gases are acidic gases except …………………………
a. sulpher dioxide
b. sulphur trioxide
c. nitrogen oxides
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1 0 – burning of fuel produces harmful gases such as ……………………….
a. carbon dioxide
b. carbon monoxide
d. nitrogen oxide
write the scientific term:
d. ammonia
d.
a
and
b.
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1 – a set of chemical formulae and symbols expressing the reactants , the products ad the
reaction condition.
………………………………………………………………….
2 – breaking the reactants bonds and forming new ones among the products.
………………………………………………………………………. .
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3 – the gas which acts as greenhouse.
…………………………………………………
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4 – poisonous gases that affect on both the eye and the nervous system.
…………………………………………………………………………………
Give reasons for :
1 – a chemical equation should be balanced?
……………………………………………………………………………………………………………………………………
2 – CO2 gas acts as greenhouse effect?
………………………………………………………………………………………………………………………………. .
3 – Carbon monoxide is a dangerous gas?
…………………………………………………………………………………………………………………………………
4 – chemical reactions have useful and harmful effects?
………………………………………………………………………………………………………………………………. .
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