Chemical Reactions and Equations Notes PDF

# Chemical Reactions and Equations - **Chemical reaction:** A process in which new chemicals are formed. - **Example:** Hydrogen gas reacts with oxygen gas to produce water under some conditions. - Hydrogen + oxygen → water - H2(g) + O2(g) → 2H2O(l) ## Characteristics of a Chemical Reac...

# Chemical Reactions and Equations - **Chemical reaction:** A process in which new chemicals are formed. - **Example:** Hydrogen gas reacts with oxygen gas to produce water under some conditions. - Hydrogen + oxygen → water - H2(g) + O2(g) → 2H2O(l) ## Characteristics of a Chemical Reaction - Formation of precipitate - Evolution of a gas - Colour change - Temperature change - State change - **Example:** - Baso4(l) - (s) + O2(g)CO2(g) - Exothermic / Endothermic ## Balanced Chemical Reaction - The number of Atoms of each element in a chemical Equation should be the same as LHS and RHS. #### Why Balance? - **Conservation of mass:** The total mass of Reactant should be equal to the total mass of products. #### Tricks - First Balance Metals (Zn, Fe, Na, Al, Mg, Mn, Cu, Ca, Pb, Ba) - Second Balance Non-metals (Cl, Br, S, N, C) - Third Balance oxygen then Hydrogen #### Examples - (1) Zn + 2HCl → ZnCl2 + H2 - (2) 3Fe + 4H2O → Fe3O4+4H2 - (3) Fe2O3 + 2Al → Al2O3 + 2Fe - (4) 3Bacl2 + Al2(SO4)3 → 3Basoy + 2AlCl3 - (5) 2Pb(NO3)2 → 2P60 + 4NO2 +02 ## Types of Chemical Reaction - **(1) Combination Reaction:** Two or More reactant combine to form a single product. - A + B → AB - 2Mg(s) + O2(g) → 2MgO(s) + Heat - **Important points:** - Mg burns with Dazzling white flame - A white Mgo powder in watch glass - Heat Energy releases so temperature increases - Combination and Exothermic Reaction. - Fox + Mug → Mgo (Dazzling white light produce) - CaO(s) + H20(l) → Ca(OH)2 (aq) + Heat - **Important points:** - Rise in temperature (exothermic). - Quick lime reacts vigorously with water. - Water added slowly because Reaction is exothermic. - Quick lime used in making cement. - Combination and Exothermic Reaction. - **Other Examples of Combination Reaction:** - (1) Burning of coal. C (S) + O2→ CO2(g) - (2) formation of water from H2(g) and O2(g) 2H2(g) + O2(g) → 2H20(1) - **(2) Decomposition Reaction:** - One reactant breaks into two or more products - AB → A + B - Decomposition - Electricity (electrochemical) - HEAT (Thermal) - LIGHT (Photochemical) - **Example:** CaCO3(s) +Heat → CaO + CO2 (g) - Used in making cement. - **Important points:** - Ferrous sulphate crystals lose water and colour changes from pale green (Fesoy. 7H20) to white (Fesoy) on heating. - Further heating decomposes Fesoy to Fe203 (Reddish-brown) - (i) **THERMAL DECOmPosition** (Thermolysis) - **Trick:** Green + Heat → Dirty white + Heat → Brown - 2feSOy (s) + Heat → Fe2O3(s) + SO2(g) + S03(9) - SO2 - sulphur dioxide - SO3 - sulphur trioxide - **Important points:** - Smell of burning sulphur (matchstick) → smell of 502(g) - 502(9) and s03(9) are air pollutant and acidic in nature. - Thermal Decomposition and Endothermic Reaction. - **Example:** 2Pb(NO3)2 (S) + Heat → 2PbO(s) + 4NO2(g) + O2(g) - **Important points:** - Cracking sound. - Brown fumes of NO2(g) irritate smell. - Yellow solid residue (Pb0%). - NO2 gas is acidic in nature and turns moisture blue litimus red. - Thermal Decomposition and Endothermic Reaction. - **(2) ELECTROLYTIC DECOMPOSION** (Electrolysis) - **Example:** 2H20(1) + Electric → 2H2(g) + O2(g) - **Important points:** - Volume of gas (H2:02=2:1) - Burning of candle - Pop sound and candle extinguish - Combustible but not supporter of combustion - Candle burns more brightly - Not combustible, but supporter of combustion - Pure water is poor conductor of electricity so a few drop of acids is added, which acts as electrolyte and conduct electricity. - **(3) PHOTOCHEMICAL DECOMPOSITION** (Photolysis) - breaks due to light. - 2AgCl(s) + sunlight → 2Ag(s) + Cl2(g) - 2 AgBr(s) + Sunlight → 2Ag(s) + Br2(g) - **Used in Black and White Photography.** - **This is why Agci and AgBr are kept in Black colour bottles to protect from sunlight.** - **Displacement Reaction** - More Reactive element form its compound - Trick: Kudi Naal Car Mango Alto Zisko Fir Lekar Hum Chale Mathura Sath Ghumne - A + BC → AC + B - **Example:** Zn(s) + CuSOy (aq) → Znsoy + Cu(6) - **Reactivity Series:** - **Less Reactive.** - **Example:** - Fe(s) + CuSO4(aq) → Fesoy (aq) + Cu(s) - **Observations:** - H2 gas is colourless and odorless, burn with pop sound and extinguishes burning candle. - Temperature increases, reaction is highly exothermic. - Dilute acid is used as reaction is highly exothermic and conc acid can lead to more exothermic and dangerous reaction. - **Double Displacement Reaction:** Exchange of ions between Reactants. - AB + CD → AD + BC - **Example:** Na2SO4(aq) + Bacl2 (aq) → BaSO4(s)↓ + Nacl - **Observations:** - White insoluble substance (precipate) of Basoy is formed. - Double Displacement and precipitation reaction. - **Precipitation Reactions:** - When two aqueous soluble-soluble solutions react to form a semi-soluble / insoluble salt, the salt is called precipitate, and such reaction is precipitation Reactions. - **Example:** Pb(NO3)2 (aq) +2KI (aq) →PbI2 +2KNO3 - **Important Points:** - Yellow insoluble substance (precipate) of PbI2 is formed. - Double displacement and precipitation reaction. ## **HEAT ÎN REACTIONS** - **Exothermic Rn:** A + BC + Heat → A + B - **Examples:** - Respiration - Burning of natural gas - Decomposition of vegetable into compost. - Burning of Mg Ribbon - Quick lime with Water - CaO(s) + H2O(l)→Ca (OH)2 +Heat - **Endothermic Rn:** A → B+c + Heat - **Examples:** - All Examples of Decomposition reaction. - Fesoy(s) + Heat → fe203(s) + SO2(g) + S03(g) - CaCO3(s) + Heat → CaO(s) + CO2(g) - Pb(NO3)2 (5) + Heat → PbO(s) + NO2(g) + O2(g) - (see example of decomposition rn) ## Oxidation and Reduction - **Oxidation:** - gains oxygen. - loses hydrogen. - it is called oxidation of (A) and (A) is said to be oxidised. - Loss of electron. - **Example:** - CU(s) + 02(9) + Heat CuO (5) - (Reddish/Brownish) - **Reduction:** - gains hydrogen. - loses oxygen. - it is called reduction of (B), and (B) is said to be reduced. - Gain of electron. - **Example:** - C40(s) + H2(g) + Heat Cu (s) + H20 - (Black colour) - **Redox Reaction:** The Reaction in which oxidation and Reduction occurs. - **Example:** Zno + C → znfco - **Trick:** Jiska hoga Oxidation wo banega Oxidising agent. Jiska hoga Reduction wo banega Reducing agent. ## Physical and Chemical Change - **Physical Change:** - No chemical reaction happens. - Shape, size, state, etc may change. - **Examples:** - Boiling water from the evaporating dish. - Melting of ice to give water. - Melting of wax. - Crushing a paper cup. - Grystallisation. - **Chemical Change** - A chemical reaction happens. - Shape, size, colour, etc may also change. - **Examples:** - Respiration - Food Digestion. - Food Cooking. - Rusting of iron - Curd from milk - Fermentation of grapes. - Burning of paper. ## Corrosion - When a metal is attacked by substances around it such as moisture (water vapourt oxygen), acid etc it is said to be corrode, and this process is called corrosion. - **Example:** - (1) Rusting of Iron. - (2) Tarmishing of copper. - Copper + H20 + C02 → copper Hydroxide + copper carbonate (green) - (3) Tarnishing of silver. - Silver + H2S → silver sulphate (Black) - Silver + O2 → (no change) - **Note:** Corrosion is an example of oxidation. ## Rancidity - The taste or smell of food material containing fat/oil changes when it is left exposed to air for a long time. - Oxidation of fat/Oil present in food material causes Rancidity. - **Prevention** - Antioxidants - Airtight container - Bag of chips (Flushed with Nitrogen gas)