Tiêu đề Chapter - 1 Chemical_Reactions_and_Equations.pdf ✅

ChemContent Chemical Reactions and Equations ● Most of the substance around us undergoes various changes. Some of these changes are temporary with no new substance being formed. They are called physical changes. Example: Water changes to steam on boiling but no new substance is formed(Even though steam and water look different when they are made to react with a piece of Na, they react the same way and give the exact same products). This involves only a change in state (liquid to vapour). ● A substance is said to undergo a chemical change when the chemical properties of a substance alter. As a result, there is either formation or breaking of atomic bonds at the molecular level. Some characteristics of a chemical change are: o New substances are produced during a chemical reaction. o Changes in energy are involved. o During the reaction, there occurs a change in mass. o There is a permanent alteration. Examples: ● Cooking of food ● Rusting of iron ● Heating of Lead nitrate ● Souring of milk ● Ripening of fruit. Chemical Equation Writing Chemical Equations ● In a chemical reaction, the reactants are written on the left hand side and the products on the right hand side of the equation. ● An arrow (→) pointing towards the products is inserted between the reactants and the products. It also represents the direction of the reaction. ● A single arrow (→) indicates the direction in which the reaction proceeds. ● A double arrow ( ) indicates a reversible reaction, i.e. the products recombine to form the reactants. ● A plus sign (+) is inserted between two or more reactants or products formed. ● If reactions are carried out under specific conditions of temperature, pressure, catalyst etc., then these conditions are mentioned on the arrow. ● The chemical equation can be made more informative by mentioning the physical states of the reactants and products. ● If gas is liberated as a product, then it is represented by an arrow pointing upwards (↑). If the product formed is in the form of a precipitate, it is represented by an