Tiêu đề Chapter - 1 Chemical_Reactions_and_Equations.pdf ✅

ChemContent arrow pointing downwards (↓). Balancing the Chemical Equations ● In a balanced chemical equation, the total number of atoms of each element of the reactants on the left hand side of the equation is equal to the number of atoms of the products formed on the right hand side of the equation. ● The total mass of the reactants is equal to the total mass of the products or the number of atoms of each element before the reaction and after the reaction is equal. Steps Involved in Balancing a Chemical Equation Consider the chemical reaction between magnesium and oxygen to understand the steps involved in balancing a chemical equation. Step 1 Let us first write the word equation for this reaction. Magnesium + Oxygen → Magnesium oxide Step 2 Write the chemical equation for the reaction between magnesium and oxygen. Mg + O2 → MgO Step 3 Count the number atoms of an element occurring on both L.H.S. and R.H.S. in this equation. Mg + O2 → MgO Component Reactant Product Magnesium 1 1 Oxygen 2 1 This is an unbalanced equation. Step 4 ● To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation. ● Choose a reactant or a product which has the maximum number of atoms in it. In that compound, select the element which has the maximum number of atoms. In this equation we shall select MgO i.e. magnesium oxide and the element oxygen in it. ● To balance the oxygen atoms, let us multiply magnesium oxide molecule by 2 on the right hand side. The equation can now be expressed as, Component Reactant Product Magnesium 1 1 × 2 = 2

ChemContent ● Exothermic Reaction: The reactions accompanied by the evolution of heat are called endothermic reactions. 2. Decomposition Reaction A chemical reaction in which a single compound splits into two or more simple substances is called a decomposition reaction. Correct way of heating the boiling tube containing crystals of ferrous sulphate and of smelling the odour For example: When mercuric oxide is heated in a crucible, the orange-red powder begins to darken and a silver mirror begins to deposit on the cooler parts of the crucible. ● Thermal Decomposition Reaction: The decomposition reactions carried out by heating are known as thermal decomposition reactions. ● Photochemical reaction: The chemical reactions which proceed with the absorption of light energy are called photochemical reactions. 3. Displacement Reaction Reactions in which the more reactive element displaces the less reactive element from its compound are called displacement reactions. Iron nails dipped in copper sulphate solution For example: Zinc displaces copper in copper sulphate to form zinc sulphate.