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Types Of Changes

Subject: Chemistry<br>By: Jinsi Hirpara, Grade VII

Jinsi
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Types Of Changes

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  1. Did you know??? -Antoine Lavoisier,a french nobleman in the 1700s was the first one who began to experiment with different chemical reactions. Types of Changes - Types of Chemical Reactions By Jinsi Hirpara,VII CM 1B

  2. Types of Chemical Reactions - Chemical Changes There are mainly 4 types of chemical reactions of chemical changes namely: 1.Combination/synthesis reactions 2.Decomposition reactions 3.Displacement reactions 4.Double decomposition reactions

  3. 1.Combination/Synthesis Reactions A combination reaction is a general category of chemical reactions.It can be defined as a chemical reaction in which 2 or more substances combine to form a single substance under suitable conditions. Combination reactions are also known as synthesis reactions because in these reactions new substances are synthesized.

  4. The general form of combination reaction is: A + B AB Reactions: • 2Na(s) + Cl(2)(g) 2NaCl2 • S(s) + O2 (g) SO2(g) • H2(g) + Cl2(g) 2HCl • Cao(s) + H2O(l) Ca(OH)2 (aq) + heat

  5. Activity To Demonstrate Combination reactions • A combustion spoon • A piece of Sodium • A glass jar Materials

  6. Procedure 1.Take a small piece of sodium in a combustion spoon and heat it in air 2.Then plunge the molten sodium into a gas jar of oxygen. Observation- Sodium burns with a yellowish flame to form yellowish sodium peroxide. The reaction can be represented as-2Na + O2 Na2O2 Sodium + oxygen sodium peroxide (yellowish powder)

  7. 2.Decomposition Reactions Decomposition reaction is defined as the reaction in which a single compound splits into 2 or more simple substances under suitable conditions.It is just the opposite of the combination reactions. In a Combination reaction,a substance is formed as a result of combination chemical combination whereas in a decomposition reaction,the substance breaks into new substances

  8. The general form of a decomposition reaction is: AB A + B Reactions: • CaCO3(s) CaO(s) + CO2(g) • 2NaCl(l) 2Na(s) + Cl2(g) • 2AgCl(s) 2Ag(s) + Cl2(g) • H2O2(l) 2H2O(l) + O2(g) heat/light electricity heat electricity sunlight sunlight

  9. Materials Activity to demonstrate Decomposition reactions • Bunsen Burner • Ferrous sulphate crystals • Test tube holder • Boiling tube

  10. Procedure 1.Take about 2g of ferrous sulphate crystals in a dry boiling tube and note the colour of the crystals 2.Hold the boiling tube with a test tube holder and heat the boiling tube over the flame of a burner. 3.Smell the gas being emitted and observe the colour of the crystals after heating. Observation- The green colour of ferrous sulphate crystals first change to white and then a brown solid(ferric oxide),SO2 and SO3 gasses are formed.

  11. The reactions can be represented as- • FeSO4.7H2O FeSO4 + 7H20 Ferrous sulphate Anhydrous ferrous sulphate + 7H2O • 2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g) Anhydrous Ferric Oxide + Sulphur dioxide + Ferric Trioxide Sulphur Trioxide = On heating = delta

  12. Types of Decomposition Reactions Decomposition reactions are mainly classified into 3 types- 1.Thermal decomposition reactions Thermal decomposition is a reaction where the decomposition happens by HEATING. • Decomposition of calcium carbonate-Calciumcarbonate(limestone)decomposes into calcium oxide(quick lime) and carbondioxide when heated.Quick lime is the major constituent of cement. CaCO3(s) CaO(s) + CO2(g)

  13. 2.Electrolytic decomposition reactions Electrolytic decomposition is a reaction where the decomposition happens by passing ELECTRICITY through it. • Decomposition of sodium chloride - On passing electricity through molten sodium chloride,it decomposes into sodium and chlorine. 2NaCl(l) 2Na(s) + Cl2(g)

  14. 3.Photochemical decomposition reactions Photochemical decomposition is a reaction where the decomposition happens during the presence of SUNLIGHT. • Decomposition of silver chloride - Place a small quantity of silver chloride(AgCl)taken in a watch glass under sunlight for some time.The crystals slowly acquire a grey colour.On analysis,it is found that the sunlight has caused decomposition of silver chloride into silver and chlorine. 2AgCl(s) 2Ag(s) + Cl2(g)

  15. 3.Displacement Reactions Displacement Reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. A reactivity series of metals and halogens needs to be followed for displacement reactions. The general form of displacement reactions is : A + BC AC + B

  16. Reactivity Series of Metals Reactivity series of Halogen

  17. Reactions - • 2Al(s) + 3CuSO4(aq) 3Cu(s) + Al2(SO4)3(aq) • Fe(s) + Pb(NO3)2(aq) Fe(NO3)2(aq) + Pb(s) • Cl2(g) + 2NaBr(aq) 2NaCl(aq) + Br2(g) • Br2(g) + 2KI(aq) 2KBr(aq) + I2(aq) • Mg(s) + 2HCl MgCl2(aq) + H2 • 2K + H2SO4 K2SO4 + H2

  18. Materials Activity to demonstrate Displacement Reactions • Zinc Granules • Conical flask • Hydrochloric acid

  19. Procedure 1.Take the conical flask and put some zinc granules in it. 2.Add Hydrochloric acid to it and then observe the changes Observation - Bubbles start coming and the conical flask becomes warm. The zinc displaces the hydrogen to form hydrogen gas and the resulting solution is zinc chloride. Zinc reacts quickly with the acid to form bubbles of hydrogen. Zn + HCl ZnCl2 + H2

  20. 4.Double Decomposition/Displacement Reactions Double displacement reactions are defined as the chemical reactions in which one component each of both the reacting molecules is exchanged to form the products. The general form of double displacement reaction is -

  21. Double displacement reactions are further classified as - 1.Neutralization reactions ACID + BASE SALT + WATER • HCL(aq) + NaOH(aq) NaCl(aq) + H2O(l) 2.Precipitation reactions In this reaction one of the products formed separates out as an insoluble substance which is named as precipitate( ) • Pb(NO3)2 (aq) + 2Nal (aq) Pbl2 (s) + 2NaNO3(aq)

  22. PROCEDURE Take the solution of silver nitrate in a test tube and add dilute hydrochloric acid to it. Observation- A white,curdy precipitate is formed. AgNO3 + HCL AgCl + HNO3 (precipitate) Activity to demonstrate Double displacement reaction MATERIALS • Silver nitrate solution • Test tube • Dilute Hydrochloric acid

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