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Revision Notes on Chemical Reactions, and Equations, , Chemical Reactions and Equations, , Any process that involves the rearrangement of, structure of the substance or conversion of, reactants into products is defined as Chemical, Reaction., , For a Chemical Reaction to occur, the change, can be observed in the form of , e Change in State: Melting of ice into water., , e Change in Colour: Iron rusting which has colour, change from silver to reddish brown., , , , 4Fe + 20, xH.,0 (moisture) 2Fe,03. xH,O, Iron oxygen Hydrated, iron [III]oxide, (Rust), , , , , , , , e Change in Temperature: There are two types of, reaction i.e Exothermic and Endothermic, Reaction.
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Exothermic Reactions: Those reactions in which, energy is released in the form of heat are called, Exothermic Reactions., , Examples (1) All combustion reactions e.g., CH4+ 202 —> CO2 + 2H20 + Heat, (2) Thermite reactions e.g., 2A1 + Fe203 —> 2Fe + Al2O3 + Heat, , Combinations are generally exothermic in nature., The decomposition of organic matters into, compost is an example of exothermic reaction., , Endothermic Reactions: Those reactions in which, energy is absorbed are called Endothermic, Reactions., , Examples , Heat, , also, the reaction of photosynthesis , Sunlight, 6CO, + 6H,0, , , , Chlorophyll CeH120¢ = ony, , ¢ Evolution of any gas: When Zinc reacts with, sulphuric acid it gives hydrogen gas., , Zn + H2 SO4 = ZnSO,q + H2, , Formation of Precipitate: When a soluble, carbonate reacts with Barium, Barium Carbonate, precipitate can be observed.
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Change in State, , Some chemical reactions are characterized by a, change in state., , e When wax is burned (in the form of wax candle,), then water and carbon dioxide are formed., , e Now, wax is a liquid whereas carbon dioxide is a, gas. This means that during the combustion, reaction of wax, the physical state changes from, Solid to liquid and gas., , Physical Change, , e In this change identity of the substance remains, same., , e For Example, Melting, Boiling etc., , Chemical Change, , e The identity of the substances change, , e Reactants are converted into substance due to, formation or broken down of older bonds, , ao 2 a a, + —, , ao, , 2H, O, 2,0
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Chemical Equation, , The symbolic representation of chemical reaction, using symbols and formulae is known as Chemical, Equation. For this, reactants are written in left, hand side whereas products are written on the, right., , Balanced Chemical Equation, , A balanced chemical equation is the one where the, number of atoms involved in reactants side is, , equal to number of atoms on product side., , Eq.1. Example of Balanced Chemical Equation, , , , Steps to form Balanced Equation, , To show how to balance the equation, the, following equation is used, Fe +H20 — Fe304 + H2, , Step 1: First of all, draw the boxes around each, formula as shown below, Step 2: Find out the number of atoms of each, element. For Example, on reactant side, 1 for Fe, 2, , H, and 1 O and on product side we have, 3 for Fe, 4, for O and 2 for H., , Step 3: Start to balance the equation with the, compound having maximum number of atoms., While balancing does not alter the formula of the, compound., , , , Step 4: One by one balance each element on, reactant and product side.
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Step 5: After balancing number of atoms on both, the side of the equation, finally check the, correctness of the balanced equation., , , , Step 6: then write the symbols of the physical state, of reactants and products as shown below, 3Fe(s) + 4H20 (g) + Fe304 (s) + 4H2 (g), , This above equation represents the balanced, equation.
