Chemical Reaction and Equation class 10


Skeletal equation are usually unbalanced equation  but there are few  which need  not to be  balanced as they are already  balanced

SKELETON  EQUATION                                                   BALANCED EQUATION

C s.+ O2 g ———-> CO2g     ———————-        Cs+ O2g ——–>CO2 g

Zn s + H2SO4 l ——-.> ZnSO4 + H2 g ———-Zn s +H2SO4 ———-> ZnSO4 + H2 g

When two or more substance react with each other the process in which new substances with new properties are formed itis called chemical reaction. The chemical reaction takes place is in form of change in state, change in colour ,change in temperature and evolution of gas .

REACTANTS : The substances that takes part in chemical reaction.  They are on the left side of reaction

PRODUCTS : The substances which are formed after the chemical reaction. In form of digestion of food,Respiration ,Rusting of iron, formation of curd.  They are on the right side of reaction.

Znic + Sulphuric acid (reactant) ————–> Znicsulphate  + Hydrogen (product)

 Zn ( s )+ H2SO4  ( l ) (reactant)————–> ZnSO4 +H2 ( g)  (prodqt)

CHEMICAL EQUATION : A chemical reaction can be represented by chemical equation  which involve symbols of the elements /chemical formula  of reactant and product with their physical state along with temperature,pressureand use of catalyst if possible should be mentioned such as Magnesium is burnt in air to form magnesium oxide but before doing so Mg ribbon must be cleaned nicely because it readily react with oxygen to form MgO which  do not burn in air.

2 Mg + O2 ———->  2MgO

this is a balanced  equation . The balanced equation obeys the law of mass conservation that mass can neither be created nor can be destroyed but transformed in other form  so number of atoms of the elements of reactant must  be equal to number of atoms of elements of product so formed as in the above equation  two atoms of Mg react with two atoms of oxygen  gives two atoms of MgO.

H2 +Cl2 ————> 2HCl

BaCl2 + Al2(SO4)3 ———> Ba(SO4)3 + 2AlCl

2 Na +2H2O ————–> 2NaOH   + H2

A solution of barium chloride when react with sodium sulphate solution it gives insoluble  barium sulphate and  solution of sodium chloride

Ba Cl2 + Na2(SO4) ————> BaSO4 +2NaCl.

Sodium hydroxide solution (water) react with hydrochloric acid (water) gives sodium chloride and water

NaOH (aq) + HCl (aq) ———–>NaCl +H2O

TYPES OF CHEMICAL REACTIONS : Ther are various types of chemical reaction

i) COBINATION REACTION: When two or more elements combine to form a single element     A+B——>C example Calcium oxide (CaO)  react vigorously with water to produce calcium hydroxide (slaked lime ) (Ca (OH)2 )

Cao  (s) + H2O ———–> Ca (OH)2 aq   Quick lime ——–> slaked lime this is used in whitewash when slaked lime react with carbon dioxide from air form a thick layer of calcium carbonate gives the shiny look on walls.

Ca (OH)2   (aq)+ CO2 (g)————> CaCO3 (s)+H2 (l).

burning of coal ; C (s) + O2 (g) ——–> CO2 (g)

formation of water : 2H2(g) + O2 ——–> 2H2O (l)

EXOTHERMIC  REACTIONS : The reactions in which heat is released with the formation of products. as burning of natural gas

CH4 +2O2 ——–>CO2 +2 H2O .

The process of respiration is also as exothermic reaction

C6H12O6 (aq) +  6O2 (g) ————>6CO2(aq) + 6 H2O (l) +energy

these carbohydrates broken down to form glucose and this glucose  combines with oxygen in the cells of body and produces energy it is the respiration process. The decomposition of vegetable matter into compost is another example .

DECOMPOSITION REACTION: In this kind of reaction single compound is break into  two or more compounds.

2 FeSO4 (s) —- heated ——–> Fe2 O3 (s)+ SO2 (g) + SO3(g)

When ferrous sulphate is heated it gives ferric oxide, Sulphur di oxide and Sulphur tri oxide in form of gases. When calcium carbonate is heated gives calcium oxide and carbon di oxide

CaCO3  (s) ——-heated ———-> CaO  (s) + CO2 (g)

when lead nitrate is heated it gives lead oxide and nitrogen di oxide (brown colour gas)

2 Pb (NO3)2(s)   ——–heated ——–>  2PbO (s) + 4 NO2 (g) + O2 (g)

White silver chloride turns into grey  in sunlight this is due to decomposition of silver chloride and chlorine by light .2 AgCl —-sunlight ———-> 2Ag (s) + Cl2 (g)

2 AgBr (s) ——-sunlight———–> 2Ag + Br2 (g) this reaction is used in black and white photography .

DISPLACEMENT REACTION : In this kind of reaction more reactive substance displaces the less reactive metal such as when iron nail dipped in copper sulphate the blue colour of copper sulphate fades into white due to the formation of iron sulphate.  A+BC–>AC +B

Fe (s)  + CuSO4(aq) ————> FeSO4 (s) + Cu (s)

Zn (s) + CuSO4 (aq) ————> ZnSO4 (s) + Cu (s)

Pb (s)  +CuCl2 (aq) ————–> PbCl2 (s) + Cu (s)   Znic and lead are more reactive.

DOUBLE DISPLACEMENT REACTIONS:   In this reaction the displacement of one element ot the other and vice versa. AB +CD —-> AD +CB. In this reaction white substances is obtained  ,insoluble in water  this is called precipitation and the reaction is the precipitation reaction. When sodium sulphate (aq) is reacted with Barium chloride (aq) it gives the insoluble precipitate of Barium sulphae and sodium chloride solution

Na2SO4 + BaCl2————-> BaSO4 (white ppt ) + 2NaCl

ELCTROLSIS OF WATER  :  When acidified water is electroysised  with the help of two electrode water molecule breaks into  H+ and OH- ion  at anode positive charge electrode oxygen is obtained and at negative charge cathode hydrogen gas is produced fig from book NCERT water electrolysis

OXIDATION AND REDUCTION When oxygen is added to  or hydrogen is removed from or electrons are remove from any substance such substances are said to be oxidised and they help in reduction so they are also called reducing agent .

When Hydrogen is added or oxygen is removed from or electrons are added to any substance it is said to be reduce as it help in oxidation so called oxidising agent

Copper (II)  when react with oxygen it becomes black in colour due to oxygen  copper is oxidised

2Cu + O2 ——–> 2CuO  (BLACK)

CuO  +H2 ———> Cu + H2O   (BROWN)  reduced as oxygen is removed hydrogen is gaining oxygen therefore oxidised. In this reaction one is oxidise whereas other os rediced so this reaction is called redox reaction.

ZnO + C————-> Zn +CO    or

MnO2 +4HCl——–> MnCl2 +2H2O + Cl2

In the above reaction  ZnO and MnO2 are reduced to Zn and MnCl2

CORROSION : When  a metal is attacked by the substances around it suchas moisture, acids etc  it is said to be corrode the process is called corrosion .Brownish powder formed on iron  called rusting , black coating on silver due to sulphide and green surface on copper are the example of corrosion.

RANCIDITY : When fats and oil are oxidised they become rancid it’s smell and taste changes for this antioxidant are added to foods containing fats and oil, that is keeping food in airtight containers which slow down the oxidation. Chips manufacturers flush bags of chips with the inert gas such as nitrogen to prevent the chips from getting rancid and oxidised.






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