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Note On Chemical Reaction And Equation

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Published in: Chemistry
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GRADE 10 CBSE CHEMISTRY CHAPTER 1

Azra S / Al Ain

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  1. CHAPTER 1: CHEMICAL REACTIONS AND EQUATION Chemical Reaction: The process in which a substance or substances undergo change to produce new substances with new properties. Reactants: The substance which takes part in a chemical reaction. Product: the new substance formed in a chemical reaction. Condition, if any. Na + H20 NaOH + H2 products reactants A chemical reaction involves or recognized by: o change in state, o color, o by evolution of gas o by change in temperature Chemical Equation: Representation of chemical reaction using symbols and formulae of the substances. Skeletal chemical equation: A chemical equation which simply represents the symbols and formulas of reactants and products taking part in the reaction is known as skeletal chemical equation for a reaction. Balanced Equation: A balanced equation is one in which the number of atoms on the reactant and product sides are equal. Law of conservation of Mass : Matter can neither be created nor destroyed in a chemical reaction. So number of elements involved in chemical reaction should remain same at reactant and product side. Types of Reaction I. Combination Reaction: The reaction in which two or more substances combine to form a new single substance. A general combination reaction: Examples: When magnesium is burnt in the air (oxygen), magnesium oxide is formed. In this reaction, magnesium is combined with oxygen. Mg(s) + O (g) —i 2MgO(s) Magnesium + Oxygen —+ Magnesium Oxide Calc O xid e Qui e Calciurn hydroxide (slaked e) slaked lime is used for white washing walls. It reacts with to form Calcium Carbonate and gives a shiny finish to the walls.
  2. (ii) Burning Of Coal 2 c +2 02...........>2 c02 carbon + oxygen Carbon Dioxide. (iii) Formation of water + 02(g) -+ 2H20(1) Exothermic Reactions: Reaction in which heat is released along with the formation of products. eg.. + 2049) + 21120(g) NOTE: Respiration is a type of endothermic reaction. During digestion, food is broken down into simpler substances. These carbohydrates are broken down to form glucose. During respiration this glucose combines with oxygen in the cells of our body and provides energy. C6H1206(aq) + 602(aq) -+ 6C02 (aq) + 6H20(1) + energy Il. Decomposition Reactions: The reaction in which a single substance decomposes to give two or more substances. Decomposition reactions can be of three types: 1. 2. Thermal Decomposition:- When a decomposition reaction is carried out by heating. 2 Faso,cg + SOY(S Fø•rozz Fø•ric Oxi& Gree2Colur —i Reddsh b•own Colour CaC03(s) CaO(s) + C02(g) (Limestone) (Lead nitrate) (Quick lime) 2PbO(s) + (Lead oxide) 4N02k) + (Nitrogen (Oxygen) dioxide) Electrolytic Decomposition:- When a decomposition reaction is carried out by electric current.
  3. 3. Light Decomposition:- When a decomposition reaction is carried out by light. e.g. 2AgCl(t) + Cl: White colour grey clour Silver bromide behaves similarly 2Ag + The above two reactions are used in black and white photography NOTE: Reactions in which energy is absorbed are known as endothermic reactions. Endothermic Reactions : The reactions which require enerw in the form of heat, light or electricity to break reactants are called endothermic reactions. Ill. Displacement Reaction: Reaction in which a more reactive element displaces a less reactive element from its compound. Fe(s) + CuSO.(aq) (Copper sulphate) Zn(s) + CuS04(aq) —i (Copper sulphate) Pb(s) + CuC12(aq) —9 (Copper chloride) FeSO.(aq) + cu(s) (Iron sulphate) ZnSO , (aq) + (Zinc sulphate) PbC12(aq) + (Lead chloride) Cu (s) Cu(s) potassium most reactive K sodium magnesium aluminiurn carbon zinc iron lead hydrogen COP per silver g Old platinurn least reactive pt Please Stop Calling Me Careless Zebra nstead Try Learning COPPER Saves GOLD IV. Double Displacement Reaction: The reaction in which two different atoms or group of atoms are mutually exchanged. eg..Na: SO. (aq) Baa: (aq) + 2NaCl (aq) Sulphate Chloride Sulphate Chloride A white substance is formed due to above reaction. The insoluble substance i.e., BaS04 is called precipitate. Precipitation Reaction — Any reaction that produces a precipitate is called a precipitation reaction. e.g.Pb(N03): + u) Lazd Nitrae 2M -+Pb1: +2Kvq (aq) u) Potæsizcn La-ad Potassizcn Iodå Idi& Nitrate the downward facing arrow represents the formation Of precipitate
  4. v. REDOX REACTION - The reaction in which one reactant gets oxidized while other gets reduced. Oxidation: Oxidation is either the gain of oxygen or loss of hydrogen. Heat e. g. 02 Reduction: Reduction is the loss of oxygen or gain of hydrogen. Oxidation Cu+H,O Reduction eg.. ZnO+ C Zn + CO Mn02 + 4HC1 -+ MnC12 + 2H20 + C12 Corrosion: When a metal is exposed to moisture, air, acid etc. for some time, a layer of hydrated oxide is formed which weakens the metal and hence metal is said to be corroded. (i) Rusting of iron. i.e. Reddish-brown coating on iron of Fe203 is formed. (ii) Black coating on Silver (iii)Green coating on copper. NOTE: Corrosion can be prevented by painting, oiling the surface, electro-plating or by galvanization. Rancidity: When fats and oils are oxidized, they become rancid and their smell and taste change. Antioxidants are added to foods containing fats and Oil. Prevention: (i) (ii) (iii) (iv) N2 gas is added to packet of chips to prevent oxidation of fats and oils. Adding antioxidants keeping food in airtight container Refrigeration

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