Chapter 1 Notes

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Chemical Reactions 

 Chemical Reactions are the process in which new substances with new properties are formed.

In a chemical reaction, reactions are: • transformed into Product. The Product this formed have properties, which are entirely different from those of the reactants

Reactants

The substances which takes part in a chemical reaction are called reactants.

Evolution of a gas

Some chemical reaction arey characterized by evolution of gas


Formation of precipitate


A precipitate is a solid Product which seperates cut from the Solution during a chemical reaction.


Some chemical reaction are


Characterise by the formation of precipitate


Ex-(1) When Potassium iodine solution solute is added to a Solution of lead nitrate, then a yellow precipitate of that iodine is form 2KI + (Pbno3)2


Ex-(11) When sulphuric acid is added to barium chloride solutio then a white precipitate is form bacl² +H²So⁴+2Hcl

3-Change in coloured 

some chemical reaction are characterised by change in colour.

Ex- (1) The chemical reaction b/w citric acid and Purple coloured. Potassium per magnet solution is characterises by changing in colours from Purple to coloureless

Ex-(2) A chemical reactions b/w Sulphur dioxide gas and acidifide potassium di cheronatre solution is characterics by a change in colour from arrange to green.

4-Change in temperature

Some chemical reaction are characterise by a change in temperature  The temperature may increase or decrease

Ex-(1) When aq. solution of barium hydroxide and ammonium chloride mix together to form Barium chloride, Ammonium and water


Ba(OH)2 + 2 NH4cl - Bacl2 + 2NH3 + 2H₂O


In this chemical reaction temperature falls and container gets cool.


Ex-(11) When quick lime reacts with water, then slaked lime is formed and a lot of heat energy is Produce. This heat rises the temperature Due to which Reaction mixture get hot. 

CaO + H₂O → Ca(OH)2 + heat

5-Change in state

Some chemical reaction are characterise by a change in a state

Ex-1 When wax is burned then water and carbon dioxide gas are formed

Wax (solid), water (liquid) when as carbon dioxide is a gas


Chemical equations

The method of representing a chemical reaction with the help of symbols and formula of the substance involved in it is known as a chemical equations


Balanced chemical equations


A Balanced chemical equations has an equal no. of atoms of different element in the reactant and the product.


Ex- Zn + H²S0⁴ - ZnSo4 + H2

Unbalanced chemical equations

An Unbalanced chemical equation has on no. of atom of one or more elements in the reactant end the Products.

To make equation more informations

 1- By indicating the Physical state of the reactant and Product

2- while indicating the heat changes taking place in the reaction           

3- By indicating the conditions under which the reaction take place.

By indication the Physical state of the reactant and Product.

There can be four Physical states -


1- Solid state is indicated by the symbol (S). 

2- Liquid state is indicated by symbol (l).

3-Aqueous is indicated by the symbol (Ag). 

4- Gases state is indicated by the symbol (g).


            Ex- Zn + H₂ Sog -= Zn Sag + He


Air Zn is solid, H2S04 (Sulphuric acid) is an Aqueous solution ZnS04 (zine Sulihate) is also Aqueous solutions and hydrogen is a gas.

So the equation can be written as

2n(s)+H2So⁴(aq) - ZnSo4 (aq)+H2(g)


By indicating the heat changes taking place is the reactions There are two type of reaction


(1) Exothermic reaction


(ii) Endothermic reaction


Exothermic reaction 

Those reaction in which heat is involved are Known as exothermic reaction. For ex-when carbon burns in oxygen to form Co2 and a lot of heat is produced in this reaction


         (solid) + O₂(gas) = CO₂ (gast + heat).


The combination reactions are exothermic reaction.

Endothermic reaction 

Those reaction in which heat is absorb are Known as Endothermic reaction. For ex-When calcium carbonate is heated. It decomposes to form and carbon dioxide


CaCo3(solid) + heat - Cao (S) + C0₂ (9)


Q-1 Why respiration is consider  as an exothermic. 

Ans  Respiration is an exothermic process because energy is released during the process, the carbon dioxide present in the food breaks down to form glucose.

Q-2Why Photosynthesis is considered as or endothermic.  

Ans  Photosynthesis is considered an enothermic reaction, energy for because during the process of that synthesis, energy from the sun or sunlight is being absorbed Any chemical rection that absorb heat energy from the surrounding to form product is termed the endothermic reaction

By indicating


1-If heat is required for a reaction then the sign detta (A) is It over the arrow

2. If the reaction takes place in the presence of a catalyst then the formula of the catalist is also written above or below the arrow sign in the eq- 2kclo3(S) - ²Kalo + 30 Mno²


Here delta A stands for heat Mno2 is a catalist.

Q-How many types of reaction?

Ans  They are five types of reaction.

 1 combination reaction

 2 Decomposition reaction

 3 Displacement reaction.

4 Double displacement reaction

5 oxidation and reduction reaction


Combination reaction 

Those reaction in which two or more Substance. combined to form a single substances are called combination reaction.

Ex-When carbon burns  in air it forms carbon dioxide 

Other ex- C+O2 =Co2

                  S+O2 =So2


Decomposition reaction 

Those reaction in splits up into two or more simple substances are known as Decomposition reaction. 

Ex-When calcium carbonate is heated it decomposed to form Calcium oxide and carbon dioxide.

Other ex- (1) CaCo3  heat  Cao + Co2

                  (2)2H2o    heat  2H2 +O2



Displacement reaction

 These reaction in which and element taken Place of other element in a compound are known as Displacement reaction.

Ex   2k +CuSo4 - k2So4 +Cu


Double displacement reaction


These reactions in which two compounds react by an exchange of ions an to formed a new compound are called Double displacement reactions.

oxidation and reduction reaction 

 The addition of oxygen to a substances is called oxidations. 

                                         OR

The removal of hydrogen from a substances is called oxidation.


Reduction


The addition to hydrogen to a sulphate is called reduction.

                                         OR

the removal of oxygen from a substances is called Reduction.


oxidising agent


The substances which gave oxygen form oxidation is called an oxidising agent

                                        OR

The substances which removes hydrogen is called an oxidising agent.


Reducing agent


The substances which gives hydrogen form reduction is called a reducing agent.

                                       OR

The substances which removes oxygen is called a reducing agent.


The oxidation and reduction reaction are also redox reaction.


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