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GRADE X
CHEMISTERY

CHAPTER Name:
Chemical Reactions

and Equations
Chemistry is What?
The theoretical and experimental study of nature, composition, preparation, isolation, properties, and uses of matter is
known as Chemistry
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Ex
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e
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)
In other hand, we can also say that Chemical changes are also known as chemical reaction
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Like, (i) Iron rod comes in contact of moisture and gets rusted
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(iv) Food gets digested in our body (v) We respire
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Like; Change in state; change in colour ;
evolution of a gas; Change in temperature
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Chemical Equation
When a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide
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Another method to write chemical reaction; Mg + O2 → MgO
This is symbolic form to write chemical equations
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2

Chemical Reactions and Equations

There are two part of a chemical reaction
•
•

Reactants: The substances that undergo chemical change in the reaction are the reactants
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Mg and O are reactants
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Ex
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Writing A chemical equation
A chemical equation represents a chemical reaction
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Similarly, Products are on the Right hand side (RHS) of arrow with a plus (+) sign
between them
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There
are no equal numbers of atoms of each element on both sides
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There are 2 on left and 1 on the right of arrow
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Writing Symbols of physical states:
Physical states tell us about the visible forms of elements/compound
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❖ To make a chemical equation more informative, the physical states of the reactants and products are mentioned
along with their chemical formulae
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The word aqueous (aq) is used when reactant or product is soluble in water or dissolve in water
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Writing medium/condition in presence of which reaction takes place
Sometimes we write the reaction conditions like temperature, pressure and catalyst etc
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e
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Heat
Examples:
CaCO3(s )
CaO(s)
+ CO2 (g)
(Limestone)
(Quick lime)

Precipitation Reaction:
Any reaction that produces a precipitate can be called a precipitation reaction
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The other product formed is sodium chloride
which remains in the solution
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Precipitate: This insoluble substance formed is known as a precipitate
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Ex
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The types of reaction are as follow;
(i) Combination reaction
(ii) Decomposition reaction
(iii) Displacement reaction
(iv) Double displacement reaction
(v) Oxidation and reduction reaction

1
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Combination Reaction
A reaction in which a single product is formed from two or more reactants is known as a combination reaction
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➢ Calcium hydroxide is used for white washing on walls
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Some Other Examples of Combination reactions
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Decomposition Reaction
The reaction in which a single reactant breaks down into two or more than two simpler products is known as decomposition
reaction
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It then
decomposes to ferric oxide (Fe2O3),
Sulphur dioxide (SO2) and Sulphur trioxide (SO3)
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Another Example of Decomposition Reaction
Heat
Examples:
CaCO3(s )
CaO(s)
+ CO2 (g)
(Limestone)
(Quick lime)
On heating calcium carbonate decomposes to calcium oxide and carbon dioxide
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It is white in color, caustic, alkaline and crystalline
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Uses of Calcium oxide:
(i) Manufacturing of cement
(ii) Manufacturing of various types of glass
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(iv) White washing: it is used with water

Thermal Decomposition:
When a decomposition reaction is carried out by heating, it is called thermal decomposition
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This is due to the decomposition of silver chloride into silver and chlorine by
light
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➢ All decomposition reactions require energy either in the form of heat, light or electricity for breaking down
reactants
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4

Chemical Reactions and Equations

On the basis of heat, there are two kinds of reaction
A
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(i) During the reaction large amount of heat (energy) is evolved
(ii) This heat makes the reaction mixture warm
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When we take food to get energy to stay alive
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These carbohydrates further broken down to form
glucose
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Therefore, respiration is also an exothermic reaction
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B
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3
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General formula for displacement reaction: Ab + C → Cb + A
Here C is highly reactive element which displace A from the reaction and joins b
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The
reaction is as:
(i) CuSO4(aq) + Fe(s) → FeSO4(aq) + Cu(s)
When solid zinc is placed in the aqueous solution of copper sulphate zinc displaces copper from the reaction or its compound
because zinc is highly reactive metal than copper
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(ii) CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s)
(iii) CuCl2(aq) + Pb(s) → PbCl2(aq) + Cu(s)

4
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General formula for double displacement reaction:
Ab + Cd → Ad + Cb
Example:
(i) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(ii) NaOH + H2SO4 → Na2SO4 + H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2+ H2SO4→ BaSO4 + HCl (v)BaCl2 + KSO4 →BaSO4 + KCl2

5
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The addition of oxygen to a substance or the removal of hydrogen from a substance or both is called oxidation
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(i) C + O2 → CO2
Oxidised
[Carbon gains oxygen and gets oxidised in carbon dioxide]
(ii) P4 + 5O2 → P2O5
Oxidised
[Phosphorous gains oxygen and gets oxidised in Phosphorous pentoxide]

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The addition of hydrogen to a substance or removal of oxygen from a substance or both is called reduction
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(ii)

Redox Reaction
Such reaction in which one reactant gets oxidised while the other gets reduced during a reaction is called redox reaction
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Example;

Oxidised
ZnO + C → Zn + CO
Reduced

Here oxidation and reduction both reactions take place in same reaction
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Reducing agent:
The substances which is responsible for removing oxygen or gives Hydrogen for reduction called reducing agent
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Hence CuO (copper oxide) gives oxygen for
oxidation to oxidised H2 therefore It is a Oxidising Agent
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Summary:
(a) Oxidised substance : H2
=> Which gains in Oxygen
(b) Reduced substance: CuO
=> Which looses Oxygen
(c) Oxidising Agent : CuO
=> Which provides Oxygen for oxidation
(d) Reducing Agent : H2
=> Which is responsible for removal of Oxygen

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1
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The process in which metals surface get corroded by reaction with air, water and moisture is called corrosion
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Preventing Corrosion
There are following method to prevent corrosion:
(i) By galvanisation (ii) By painting metal surfaces (iii) By oiling or greasing metal surfaces
Galvanisation: Coating of thin layer of zinc (Zn) on metal surface by electro-plating is called galvanisation
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Rancidity
The condition produced by airborne oxidation of fats and oils in foods marked by unpleasant smell and taste is called
rancidity
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(ii) Rancidity spoils the food materials prepared in fat/oil
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Oxidized food materials' taste and
smell are changed
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Preventing fat/oil containing foods from rancidity:
Fat/oil containing food can be prevented or the rate of rancidity can be retarded by using following methods:
(i) Rancidity can be prevented by adding antioxidants to fat/oil containing foods
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(iii) Rancidity can be retarded by keeping food in airtight containers that helps to slow down oxidation
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(v) Rancidity can be retarded by keeping food in a refrigerator that cause to slow down oxidation
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