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Ncert class 10 - science - chapter 1 - chemical reactions and equations

The document discusses chemical reactions, differentiating between physical and chemical changes, and explaining various reaction types including combination, decomposition, displacement, double displacement, oxidation, and reduction. It details the structure and balancing of chemical equations, emphasizing the significance of reactants and products, along with informative equations indicating physical states and reaction conditions. Additionally, it covers specific activities demonstrating chemical reactions, energy changes, and the concepts of exothermic and endothermic processes.

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Chemical Reactions•
Chemical Reactions and Equations Class X – Science Chapter 1 Chemistry
Chemical Reactions • The breaking and making of bonds between different atoms to produce new substances is called Chemical Reaction. • There are two type of changes namely physical and chemical changes. o Melting of Ice (Physical Change) o Rusting of Iron (Chemical Change) o Formation of Curd (Chemical change)
Physical change Vs Chemical Change • Any change that involves chemical changes is called Chemical reaction. Physical Change Chemical Change Change is temporary Change is permanent No new substance is formed. There is change only in physical properties. New substances are formed with entirely different physical and chemical properties Change can be reversed by simple physical methods Change cannot be reversed by simple physical methods Energy may or may not be released or absorbed Energy is released or absorbed during chemical change
Chemical Equations • The representation of chemical reactions in the form of formulae of reactants and products separated by an arrow mark is called Chemical Equation. o Word Equation Magnesium + Oxygen Magnesium Oxide (Reactants) (Product) LHS RHS o Chemical Equation Mg + O2 MgO (Reactants) (Product) LHS RHS
Balanced Equation • The same number of atoms of each element on the LHS (i.e. reactants) and RHS (i.e. products) of the equation. o Chemical Equation – Example 1 Mg + O2 MgO LHS RHS Mg  1 O  2 Mg  1 O  1 LHS RHS Mg  1 O  2 x 1 Mg  1 O  1 x 2 Mg + O2 2MgO
Balancing of Equations Mg + O2 2MgO LHS RHS Mg  1 O  2 Mg  2 O  2 LHS RHS Mg  1 x 2 O  2 Mg  2 x 1 O  2 2 Mg + O2 2MgO
Balancing of Equations o Chemical Equation – Example 2 Fe + H2O Fe3O4 + H2 LHS RHS Fe  1 H  2 O  1 Fe  3 H  2 O  4 LHS RHS Fe  1 x 3 = 3 H  2 O  1 Fe  3 x 1 = 3 H  2 O  4 3Fe + H2O Fe3O4 + H2
Balancing of Equations 3Fe + H2O Fe3O4 + H2 LHS RHS Fe  3 H  8 O  4 Fe  3 H  2 O  4 LHS RHS Fe  3 H  2 O  1 x 4 = 4 Fe  3 H  2 O  4 x 1 = 4 3Fe + 4H2O Fe3O4 + H2
Balancing of Equations LHS RHS Fe  3 H  8 O  4 Fe  3 H  8 O  4 Thus the equation is balanced!!!! LHS RHS Fe  3 H  8 O  4 Fe  3 H  2 x 4 = 8 O  4 3Fe + 4H2O Fe3O4 + 4H2
Informative Equation • Informative Equation is the representation of physical states using symbols like Physical State Representation Solid s Liquid l Gas g / ↑ Water soluble solution aq Precipitate ↓ Reaction Conditions such as Temperature, Pressure, Catalyst Indicated above or below the arrow Heat Δ
Informative Equation • Examples: 3Fe(s) + 4H2O (l) Fe3O4(s) + 4H2↑ CO (g) + 2H2 (g) 340 atm CH3OH (l) 6CO2 (aq) + 12H2O (l) Sunlight C6H12O6 (aq) + 6O2 (aq) + 6H2O (l) Chlorophyll
Type of Reactions • Combination • Decomposition • Displacement • Double displacement • Oxidation • Reduction • Redox Reaction • Precipitation • Exothermic reaction • Endothermic reaction
Combination Reaction • A reaction in which two or more reactants combine to form a single product is called chemical combination. • Burning of coal: C (s) + O2 (g) CO2 (g) (Carbon) (Oxygen) (Carbon dioxide) • Formation of Water from H2(g) and O2 (g) 2 H2 (g) + O2 (g) 2H2O (l) (Hydrogen) (Oxygen) (Water) • Formation of slaked lime: CaO (s) + H2O(l) Ca(OH)2 (aq) (Quick Lime) (Water) (Slaked Lime – Calcium Hydroxide)
Decomposition Reaction • A reaction in which a single reactant breaks down to form two or more products is known as decomposition reaction. • Three types of decomposition are thermal decomposition, electrolytic decomposition and photolytic decomposition. • Thermal decomposition – Decomposition reaction taking place in the presence of heat 2FeSO4 (s) Heat Fe2O3 + SO2 (g) + SO3 (g) (Ferrous Sulphate) (Ferric Oxide) (Sulphur (Sulphur dioxide) trioxide) 2CaCO3 (s) Heat CaO (s) + CO2 (g) (Limestone) (Quick Lime) (Carbon dioxide) 2 Pb(NO3)2 Heat 2PbO + 4NO2 (g) + O2 (g) (Lead Nitrate) (Lead Oxide0 (Nitrogen (Oxygen) dioxide)
Decomposition Reaction • Photolytic Decomposition – Decomposition reaction taking place in the presence of light. 2AgCl (s) Sunlight 2Ag (s) + Cl2 (g) (Silver Chloride) (Silver) (Chlorine) 2AgBr (s) Sunlight 2Ag (s) + Br2 (g) (Silver Bromide) (Silver) (Bromine) • Electrolytic Decomposition – Decomposition reaction taking place in the presence of electricity. 2H2O (l) Electrolysis 2H2 (g) + O2 (g) (Water) (Hydrogen) (Oxygen)
Displacement Reaction • When a more reactive element displaces less reactive element from its compound it is called displacement reaction. Fe(s) + CuSO4 (aq) FeSO4 (aq) + Cu(s) (Iron) (Copper Sulphate) (Iron Sulphate) (Copper) Zn(s) + CuSO4 (aq) ZnSO4 (aq) + Cu(s) (Zinc) (Copper Sulphate) (Zinc Sulphate) (Copper) Pb(s) + CuCl2 (aq) PbCl2 (aq) + Cu(s) (Lead) (Copper Chloride) (Lead Chloride) (Copper)
Double Displacement Reaction • The reaction in which two different ions or group of atoms in the reactant molecules are displaced it is called as double displacement reaction. Na2SO4 (aq) + BaCl2 (aq) BaSO4 (s) + 2NaCl (aq) (Sodium (Barium (Barium (Sodium Sulphate) Chloride) Sulphate) Chloride)
Oxidation and Reduction • The process of addition of oxygen to a substance or removal of hydrogen from a substance is called oxidation. 2Cu (s) + O2 (g) Heat 2CuO (s) (Copper) (Oxygen) (Copper Oxide) • The process of removal of oxygen from a substance or addition of hydrogen to a substance is called Reduction. 2CuO (s) + H2 (g) Heat Cu (s) + H2O (l) (Copper Oxide) (Hydrogen) (Copper) (Water)
Redox Reaction • The reactions in which oxidation and reduction takes place simultaneously is called redox reaction.
Precipitation Reaction • Chemical reaction which involves formation of water insoluble precipitation is called precipitation reaction. Na2SO4 (aq) + BaCl2 (aq) BaSO4 (s) + 2NaCl (aq) (Sodium (Barium (Barium (Sodium Sulphate) Chloride) Sulphate) Chloride)
Exothermic Reaction • Reactions that involve evolution of heat are called exothermic reactions. • Burning of Natural Gas CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (g) + Energy (Natural (Oxygen) (Carbon (Water) gas) dioxide) • Decomposition of vegetable into compost is also an example of an exothermic reaction.
Exothermic Reaction • Respiration is an exothermic process. • The food that we intake is broken down into simpler substances such as carbohydrates, protein, fats during digestion. • Carbohydrates thus absorbed are broken down to glucose. • Glucose combines with oxygen in the cells of our body and provides energy. This reaction is called as respiration C6H12O6 (aq) + 6O2 (aq) CO2 (g) + 2H2O (g) + Energy (Glucose) (Oxygen) (Carbon (Water) dioxide) •
Endothermic Reaction • Reactions which occur by the absorption of heat are called endothermic reaction. 2FeSO4 (s) Heat Fe2O3 + SO2 (g) + SO3 (g) (Ferrous Sulphate) (Ferric Oxide) (Sulphur (Sulphur dioxide) trioxide) 2CaCO3 (s) Heat CaO (s) + CO2 (g) (Limestone) (Quick Lime) (Carbon dioxide)
Rancidity • The process of slow oxidation of oil and fat present in the food materials resulting in the change of smell and taste in them is called rancidity. • Rancidity of food can be prevented o By keeping food materials in air tight container. o Refrigeration of cooked food at low temperature o Packing of food items like potato chips in packs containing nitrogen gas instead of air. It prevents oils and fats from reacting with air. o Avoid keeping the cooked food and food materials in direct contact with air. o By adding anti-oxidants e.g. BHA (Butrylated Hydroxy Anisole).
Corrosion • The phenomenon in which metals are slowly eaten away by the reaction of air, water, chemicals present in the atmosphere is called Corrosion. o E.g. Black coating on Silver and Green coating on Copper • Rusting of Iron is due to corrosion. It can be prevented: o By Applying paint on Iron articles, rusting (Corrosion) can be prevented. o Paint does not allow oxygen and moisture to come in contact with the surface of Iron.
Activity – 1.1 • What happens when heat is applied on Magnesium Ribbon by burning it on Spirit Lamp? Magnesium burns with dazzling light and substance formed is Magnesium oxide. 2Mg (s) + O2 (g) 2 MgO (s) Inference: o It changes state from hard metal to Powder. o Endothermic reaction. o It is a combination reaction.
Activity – 1.2 • What do you observe when Lead Nitrate reacts with Potassium Iodide solution? Lead Nitrate reacts with potassium iodide to form Lead iodide which is insoluble in water and yellow in color. Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) ↓ + KNO3(aq) (Yellow Precipitate) Inference: o It changes state from liquid to solid. o Double Displacement Reaction. o Precipitation reaction.
Activity – 1.3 • Which gas will evolve when Zinc metal reacts with dilute Hydrochloric acid? How will you identify the gas. o When Zinc reacts with dilute Hydrochloric acid, Zinc chloride is formed and bubbles of hydrogen gas are observed. o Conical flask becomes hot. Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g) + Δ (Dilute) Inference: o Evolution of Hydrogen gas (evolves with a pop sound upon a burning candle) o Exothermic reaction. o Oxidation reaction as Hydrogen is removed. o It is also a Displacement Reaction.
Activity – 1.4a • What happens when quick lime is mixed with water? o Calcium Oxide (quick lime) reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing large amount of heat. CaO (s) + H2O (l) Ca(OH)2 (aq) + Δ (Quick Lime) (Water) (Slaked Lime – Calcium Hydroxide) Inference: o Combination reaction. o Exothermic reaction.
Activity – 1.4b • What happens when Calcium Hydroxide reacts with Carbon dioxide? o Calcium Hydroxide reacts with Carbon dioxide to form Calcium Carbonate and Water. Ca(OH)2 (s) + CO2 (g) CaCO3 (s) + H2O (g) Inference: o This is a common reaction that occurs during Whitewash. Lime water (Calcium Hydroxide) reacts with Carbon dioxide in atmosphere to form thick coat of Calcium Carbonate.
Activity – 1.5 • What happens when ferrous sulphate crystals are heated in a dry boiling tube over a burner? o The green colour of ferrous sulphate crystals changes to brownish-black ferric oxide and smell of burning sulphur dioxide is observed. 2FeSO4 (s) Heat Fe2O3 (s) + SO2 (g) + SO3 (g) (Ferrous Sulphate) (Ferric Oxide) (Sulphur (Sulphur Green Brownish-black dioxide) trioxide) Inference: o Smell is due to burning Sulphur dioxide. o Thermal Decomposition reaction. o Endothermic reaction.
Activity – 1.6 • What happens when Lead Nitrate is heated in a boiling tube over a burner? o Pungent smelling, brown fumes are evolved due to NO2 gas and brownish residue of lead oxide (PbO) is left. 2Pb(NO3)2 (s) Heat PbO (s) + 4NO2 (g) + O2 (g) (Lead Nitrate) (Lead Oxide) (Nitrogen (Oxygen) Brownish residue Inference: o Pungent smell and Brown fumes are due to Nitrogen dioxide o Thermal Decomposition reaction. o Endothermic reaction.
Activity – 1.7 • Electrolysis of water. o When water is electrolysed, Hydrogen and Oxygen are emitted. 2H2O (l) Electrolysis 2H2 (g) + O2 (g) (Water) (Hydrogen) (Oxygen) Inference: o Volume of Hydrogen gas is twice the volume of Oxygen. o One of the gases catches fire and burns with pop sound indicating that it is Hydrogen. o In other gas, candle burns brightly indicating that it is oxygen. o Electrolytic Decomposition reaction.
Activity – 1.8 • Why do we store Silver chloride in dark coloured bottles? o Silver chloride turns grey in sunlight because silver metal is formed due to photolytic reaction and chlorine gas is produced. 2AgCl (s) Sunlight 2Ag (s) + Cl2 (g) Inference: o Photolytic Decomposition reaction.
Activity – 1.9 • Why does the colour of Copper Sulphate solution change when an iron nail is dipped in it? o Iron being more reactive than Copper, displaces it there by forming a iron sulphate and copper metal. Fe (s) + CuSO4 (S) FeSO4 (s) + Cu (s) (Iron) (Copper Sulphate) (Iron Sulphate) Copper (Blue) (Green) Inference: o Color changes from blue to Green due to formation of Iron sulphate. o Displacement Reaction.
Activity – 1.10 • Aqueous solution of Sodium Chloride, Sodium Sulphate and Calcium Chloride are taken in three separate test tubes. Using aqueous barium chloride how do you identify sodium sulphate? o When Sodium sulphate reacts with barium chloride, white precipitate of barium sulphate is formed. Na2SO4 (aq) + BaCl2 (aq) BaSO4 (s) ↓ + 2NaCl (s) Inference: o Sodium Chloride & Calcium Chloride do not react with Barium Chloride. Hence solution remains clear. o Upon reaction with Barium Chloride, Sodium Sulphate produces Barium Sulphate, a white precipitate. o This is a Double Displacement Reaction.
Activity – 1.11a • Why does Copper acquire a green coat when exposed to air for a long time? o Green coating is formed in copper due to corrosion. Green coating is a mixture of copper carbonate and copper hydroxide. 2Cu + H2O + CO2 + O2 Cu(OH)2 + CuCO3 Inference: o Copper on exposure to air reacts with gases and moisture in air to form Copper hydroxide and Copper carbonate
Activity – 1.11b • Why does Copper Powder turn black when heated ? o The surface of copper powder on heating becomes black as it reacts with Oxygen to produce Copper oxide. 2 Cu + O2 Heat 2 CuO Inference: o Copper Oxide formed due to combination of Copper and Oxygen is black in color. o Combination reaction o Endothermic reaction o Oxidation reaction.
Ncert class 10 - science - chapter 1 - chemical reactions and equations