Chemical Reactions & Equations Class 10 Notes PDF

CLASS 10 NOTES SCIENCE Chemical Reactions & Equations PRASHANT KIRAD  PRASHANT KIRAD Chemical Reaction: The transformation of chemical substance into another chemical substance is known as Chemic...

CLASS 10 NOTES SCIENCE Chemical Reactions & Equations PRASHANT KIRAD  PRASHANT KIRAD Chemical Reaction: The transformation of chemical substance into another chemical substance is known as Chemical Reaction. e.g.: Rusting of iron, the setting of milk into curd, digestion of food, respiration, etc. JOSH METER? Chemical changes indicate that a chemical reaction has occurred. Characteristics of chemical reactions: Formation of new substances with different Chemical Equation: properties, Change in color, Evolution of gas, Representation of chemical Evolution or absorption of heat, Formation of a precipitate, Irreversibility of many chemical reaction using symbols and reactions, Change in state of matter, Change in formulae of the substances energy. is called Chemical Equation. Example: A + B → C + D D RA Reactant Product Magnesium + Oxygen → Magnesium oxide Mg + O2→ MgO KI Magnesium ribbon burns T with a dazzling white AN flame and changes into a white powder. This powder is magnesium H oxide. It is formed due AS to the reaction between magnesium and oxygen present in the air PR Magnesium is rubbed with sandpaper to remove the oxide layer, allowing it to burn more easily. Balanced Chemical Equation: A balanced chemical equation has an equal number of atoms of each element in the reactant and product side. Law of Conservation of Mass: Mass of reactants = Mass of products. Fe+H2O→Fe3O4+H2 (Unbalanced) 3Fe+4H2O→Fe 3O4 + 4H 2 (Balanced) number of atoms of each element in reactants = number of atoms of each element in products  PRASHANT KIRAD “Experiment ka funda“: Take some lead nitrate solution in a test tube or beaker and add potassium iodide solution. A yellow precipitate of lead iodide forms immediately, and the solution changes color from colorless to yellow. “Experiment ka funda“: Take some zinc granules in a conical flask and add sulfuric acid. Bubbles of hydrogen gas will form around the zinc D metal. We verify it's hydrogen gas because the bubbles burn with a popping sound when passed through a soap solution. RA Formation of hydrogen gas by the action of Additionally, the flask becomes hot to the touch, indicating dilute sulphuric acid on zinc that the reaction releases heat along with the gas. KI T Balancing Chemical Reaction: AN 1. Identify the unbalanced equation: H 2. List the number of atoms of different elements in the unbalanced equation: AS PR 3. Start balancing the compound (reactant of product) that contains the maximum number of atoms. In that compound, balance the element with the maximum number of atoms (Balanced) “Balancing ki practice jyaada se jyaada karo” - Prashant Bhaiya  PRASHANT KIRAD More Questions to practice: 1. CO 2 + H 2 O → C6 H 12 O 6 + O 2. A solution of slaked lime Ca(OH)2 is used for whitewashing walls. It reacts with carbon dioxide in the 2. CH4 + O2 → CO2 + H 2O air to form calcium carbonate CaCO3 , which gives the walls a shiny finish after two to three days. Marble also 3. Fe 2O3 + C → Fe + CO2 has the formula CaCO3 ​. The reaction is: 4. N 2 + H2 → NH 3 Ca(OH) 2 (𝑎𝑞)+CO 2(𝑔)→CaCO 3(𝑠)+H 2O(𝑙) Types of Chemical Reactions: 1. Combination Reactions: two or more reactants combine to form single products. A + B → AB 1. Formation of Water : 2H2 +O2 →2H 2 O 2. Formation of Calcium Oxide : CaO + H 2O → Ca(OH) 2 (slaked lime) D RA KI T “Experiment ka funda“: AN Take a small amount of calcium oxide (quick lime) in a beaker and slowly add water to it. Touch the outside of the beaker, and you will feel it getting hot. This is because calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide), releasing a H large amount of heat. AS Reactions that release heat along with the formation of products are called exothermic PR chemical reactions, while those that absorb heat are known as endothermic reactions. 2. Decomposition Reactions: a single reactant decomposes to form two or more products. AB → A + B 1. Decomposition of Calcium Carbonate : CaCO3 (s) → CaO(S) + CO2 2. Decomposition of Ferrous Sulphate : 2FeSO 4 → Fe2 O3 + SO 2 + SO 3 Saari activities acche se dekhna, important h! Direct questions aa jaate h  PRASHANT KIRAD “Experiment ka funda“: Take about 2 grams of Ferrous Sulphate Crystals in a DRY Boiling Tube. They are originally green in color. Heat the boiling tube over a burner, and you will observe the magic. The green color changes to white and then finally a brown solid is formed, which is ferric oxide. Along with the color change, the smell of burning sulphur is also noticeable Thermal Decomposition Reactions: heat-induced breakdown. “Experiment ka funda“: Take 2 grams of lead nitrate powder in a boiling tube. Heat it over a burner. Brown fumes of nitrogen dioxide gas are released, filling the tube. Holding a glowing splinter over the tube causes it to catch fire, indicating the presence of oxygen gas. After the reaction, yellow lead monoxide solid remains in the tube, which appears reddish-brown when hot and yellow when cold. D RA Electrolytic Decomposition - heat-induced breakdown.. Activity 1.7: KI Hydrogen (cathode) will produce a popping sound when a burning candle is brought close. Oxygen (anode) will make the flame of the candle burn brighter. T Photolytic Decomposition - light-induced decomposition. AN “Experiment ka funda“: H White silver chloride turns grey in sunlight. This is due to the AS decomposition of silver chloride into silver and chlorine by light. PR 3. Displacement Reactions: chemical reaction in which a more reactive element displaces a less reactive element from its compound. Single Displacement: A+BC→AC+B Example: Zn+CuSO 4 →ZnSO 4 +Cu Reactivity series of metals Trick to remember reactivity reactivity series: Katrina ne car mangi alto zen ferari phir bhi haye cu mili silver audi  PRASHANT KIRAD “Experiment ka funda“: In this reaction, the iron nail turns brownish and the blue color of the copper sulphate solution fades because iron displaces copper from copper sulphate (CuSO₄) in a displacement reaction. The original deep blue color of the solution fades to light green, and the iron nail becomes covered with a red- brown layer of copper. 4. Double Displacement Reaction: Those reactions in which two ionic compounds in the solution react by exchange of their ions to form new compounds are called double displacement reactions. Double Displacement: AB+CD→AD+BC Example: NaOH + HCl → NaCl + H2O D “Experiment ka funda“: RA Take 3 mL of sodium sulphate solution in a test tube and 3 mL of barium chloride solution in another. Add the barium chloride solution to the sodium sulphate solution. A white KI precipitate will form in the test tube T AN Secret Questions: H 1. Write the balanced chemical equation for the reactions that take place AS during respiration. Identify the type of combination reaction that takes place during this process and justify the name. Give one more example of PR this type of reaction. [CBSE 2012] Solution : (i) The carbohydrates that we take in our food are oxidized to carbon dioxide and water. C₆H₁₂O₆ + 6O₂→ 6CO₂ + 6H₂O The carbon of carbohydrates and oxygen combine to form CO₂. (ii) It is an exothermic combination reaction. (iii) Decomposition of vegetable matter into compost is another example of this type of reaction. 2. Translate a balanced chemical equation with state symbols for the following i) Solutions of Barium chloride and Sodium sulfate in water react to give insoluble Barium sulfate and a solution of Sodium chloride.  PRASHANT KIRAD ii) Sodium hydroxide solution in water interacts with hydrochloric acid to produce Sodium chloride solution and water. iii) Hydrogen gas combines with nitrogen to form ammonia. iv) potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Solution : i) BaCl 2 +Na2 SO4 →BaSO 4 +2NaCl ii) NaOH+HCl→NaCl+H 2 O iii) 3H2 +N2 →2NH 3 iv) 2K+2H 2 O→2KOH+H2 5. Oxidation Reactions: Oxidation: If a substance gains oxygen or loses hydrogen during a reaction, it D is said to be oxidized. RA Reduction: If a substance loses oxygen or gains hydrogen during a reaction, it is said to be reduced. KI Redox Reaction: In a reaction where one reactant gets oxidized while the other gets reduced, it is called an oxidation-reduction reaction or redox T reaction. AN “Experiment ka funda“: When about 1 gram of red-brown copper powder is heated in a china dish, it forms a black substance, which is copper H oxide (CuO). This black coating is a result of the oxidation of copper to copper oxide. To turn the black coating back AS to reddish-brown, hydrogen gas can be passed over the heated copper oxide, causing a reverse reaction that produces copper. PR “Ox“idation: “Ox“ygen dost (gaining oxygen) or Hydrogen dushman (losing hydrogen). “Re“duction: Oxygen dushman (losing oxygen) or “Hy”drogen dost (gaining hydrogen). { Hy re! } Oxidised (+O) ZnO + C → Zn + CO Reduced (-O) Extra Knowledge!!  PRASHANT KIRAD EFFECTS OF OXIDATION REACTIONS IN EVERYDAY LIFE? Corrosion: the process by which metals are gradually destroyed by chemical reactions with substances in their environment, such as moisture and acids. This often results in the formation of an oxide or other compound on the metal's surface. Impact: Corrosion weakens the metal structure, affecting its strength and durability. Prevention: Coating metals with protective layers (e.g., paint or galvanization) helps prevent direct exposure to oxygen and moisture, reducing the risk of corrosion. Examples: Rusting of iron, Tarnishing of silver, Green coating on copper Rancidity: the spoilage of fats and oils in food, leading to unpleasant D taste and smell. This happens due to the oxidation of fats and oils when RA exposed to air. Impact: Rancidity imparts unpleasant tastes and smells to food products, KI making them unpalatable and reducing their shelf life. Prevention: Adding antioxidants, storing foods in airtight containers, and T refrigerating can help slow down or prevent the oxidation process and, AN consequently, rancidity Examples: Spoiled butter, Old cooking oil, Stale chips H AS Top 7 Questions PR 1. Why is respiration considered an exothermic reaction? Explain. Answer: Respiration is the process of breaking down food in the living body to produce energy. Respiration is considered an exothermic chemical reaction because the oxidation of glucose occurs during the process, releasing a large amount of energy, which is captured in the form of ATP. During respiration, we inhale oxygen from the atmosphere, which reacts with glucose in our body cells to produce carbon dioxide, water, and energy. The reaction is represented by the following chemical equation: C₆H₁₂O₆ + 6O₂→ 6CO₂ + 6H₂O + energy ( ATP )  PRASHANT KIRAD 2. Explain the following in terms of the gain of oxygen with two examples each. (a) Oxidation (b) Reduction. Answer: (a) Oxidation: In a chemical reaction, when oxygen is added to an element or compound to form its oxide, the element or compound is being oxidized. For example: 4Na(𝑠)+O 2 (𝑔)→2Na 2O(𝑠) H 2S(𝑔)+O 2 (𝑔)→H 2O(𝑙)+SO 2(𝑔) (b) Reduction: In a chemical reaction, when oxygen is removed from a compound, the compound is said to be reduced. For example: CuO(𝑠)+H 2(𝑔)→Cu(𝑠)+H 2O(𝑙) 2HgO(𝑠)→2Hg(𝑙)+O2 (𝑔) 3. A shiny brown-colored element ‘X’ on heating in the air becomes black. D Name the element ‘X’ & the black-coloured compound formed. RA Answer: The shiny brown-colored element is Copper metal (Cu). If the metal is heated in air, it interacts with atmospheric oxygen to form copper oxide. KI Therefore, the black-colored compound is copper oxide. 2Cu(s) + O 2 (g) → 2CuO(s). T AN 4. Why do we store silver chloride in dark-colored bottles? Answer: Silver chloride is highly sensitive to light and undergoes photolytic H decomposition upon exposure to light. This reaction occurs rapidly and causes AS the silver chloride to lose its properties, forming chlorine gas and elemental silver. Therefore, silver chloride is stored in dark-colored bottles to protect it PR from light and prevent its decomposition. 5. Write one equation each for decomposition reactions in which energy is supplied in the form of heat, light, or electricity. Answer: (a) Thermal decomposition reaction (Thermolysis): Decomposition of potassium chlorate: If heated strongly, potassium chlorate decomposes into potassium chloride and oxygen molecules. This reaction is commonly used for the synthesis of oxygen molecules. 2KClO3 +heat→2KCl+3O 2 (b) Electrolytic decomposition reaction (Electrolysis): Decomposition of sodium chloride (NaCl): On passing electricity through molten sodium chloride, it decomposes into sodium and chlorine. 2NaCl(electrolysis)→2Na+Cl 2  PRASHANT KIRAD (c) Photodecomposition reaction (Photolysis): Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide decomposes into water and oxygen molecules. 2H 2O2 +light→2H2 O+O 2 6. What is the difference between displacement and double displacement reactions? Write relevant equations for the above. Answer: A displacement reaction occurs when a more reactive substance replaces a less reactive substance from its salt solutions. A double displacement reaction occurs when a mutual exchange of metal ions happens between two compounds. In a displacement reaction, only a single displacement occurs, whereas in the double displacement reaction, as the name suggests, two displacements occur between the molecules. D Example of Displacement reaction: RA Mg+2HCl→MgCl2 +H2 Example of Double displacement reaction: KI 2KBr+BaI2 →2KI+BaBr 2 T 7. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, AN whereas copper does not. Explain why? Answero Zinc is more reactive than copper as Zinc is placed above hydrogen, H and copper is placed below hydrogen in the activity series of metals. Thus, zinc AS liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. PR Top 7 Questions 1) Clean a magnesium ribbon about 2 cm long by rubbing it with sandpaper. Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass  PRASHANT KIRAD (i). Magnesium ribbon needs to be rubbed before burning because it has a coating on its surface. A. basic magnesium carbonate B. basic magnesium oxide C. basic magnesium sulphide D. basic magnesium chloride (ii). What is the colour of magnesium ribbon? A. White B. Black C. Grey D. Yellow (iii). What is the chemical name of the powder obtained in the D A. magnesium carbonate RA B. magnesium oxide C. magnesium sulphide KI D. magnesium chloride T (iv). Which compound is formed when the powder obtained reacts with water? AN A. Magnesium sulphate B. Magnesium oxide H C. Magnesium Carbonate AS D. Magnesium hydroxide PR 2) Take a plastic mug, drill two holes at its base and insert carbon electrodes. Connect these electrodes to a 6 volt battery. Fill the mug with water such that the electrodes are immersed. Add a few drops of dilute sulphuric acid to the water. Take two test tubes filled with water and invert them over the two carbon electrodes. Switch on the current and leave the apparatus undisturbed for some time.  PRASHANT KIRAD (i). What is the ratio in which hydrogen and oxygen are present in water by volume? A. 1:2 B. 1:1 C. 2:1 D. 1:8 (ii). Which electrodes are used in this activity? A. Graphite B. Diamond C. Copper D. Coke (iii). Where is hydrogen gas collected? D A. Anode RA B. Cathode C. At both electrodes D. Hydrogen gas is not evolved in this activity KI T (iv). Which of the following is an endothermic process? AN A. Dilution of sulphuric acid B. Condensation of water vapours H C. Respiration in human beings D. Electrolysis​ AS PR Answers: 1. (i) A (ii) C (iii) B (iv) D “Class 10th Phodenge” 2. (i) C - Prashant Bhaiya (ii) A (iii) B (iv) D