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•A chemical reaction involves chemical change in which substances react to form new substances with entirely new properties. •During a chemical reaction, atoms of one element don’t change in to those of another element. Only a rearrangement of atoms takes place in a chemical reactions. •During a chemical reaction, there is a breaking of bonds between atoms of the reacting molecules to give products •Matter can neither be created nor destroyed in a chemical reaction.
A chemical reaction can be observedwith the help of any of the followingobservations:-a. Evolution of a gasb. Change in temperaturec. Formation of a precipitated. Change in coloure. Change of state
Physical change: If a change involves changein colour or state but no newsubstance is formed, then it is a physical change.Chemical change: If a change involvesformation of new substances, it is achemical change. Exothermic and endothermic reactions: Ifheat is evolved during a reaction,then such a reaction is known as Exothermicreaction. If heat is absorbed fromthe surroundings, then such a reaction is known asendothermic reaction.
Chemical equation:-The method ofrepresenting a chemicalreaction with the help ofsymbols and formulae ofthe substances involved init is known as chemicalequation.
Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS PRODUCTS
Features of a chemicalequation:-a. The reactants are written on the left handside with a plus sign betweenthem.b. The products are written on the right handside with a plus sign betweenthem.c. An arrow separates the reactants from theproducts. The arrow head pointsGet the Power of Visual Impact on your sidetowards the products and indicates thedirection of the reaction.
“Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate(s) Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state(l) A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state(aq)(g) A reactant or product in the gaseous state
Unbalanced and Balanced Equations H Cl Cl H H Cl H Cl Cl Cl H ClHHH2 + Cl2 HCl (unbalanced) H2 + Cl2 2 HCl (balanced) reactants products reactants products H 2 1 H 2 2 Cl 2 1 Cl 2 2
Balanced chemical equation: A balancedequation is a chemical equation inwhich number of atoms of each element is equal on both sidesof the equationi.e. number of atoms of an element on reactant side = numberof atoms ofthat element on the product side.As per the law of conservation of mass, the total mass of theelements presentin the products of a chemical reaction is equal to the total mass oftheelements present in the reactants.Unbalanced chemical equation:- An unbalancedchemical equation has an unequal no. of atoms of one or more elements in the reactants and products. •An unbalanced equation has unequal masses of various elements in reactants and products.
The reactivityseries•The reactivity series isa list of metalsarranged in the orderof decreasingreactivity. The mostreactive metal isplaced at the top andthe least reactivemetal is placed at thebottom.
Combination reactionCombination reaction is a reaction in which 2 ormore substances combine togive a single product. Combination reaction canbe between 2 elements,between an element and a compound orbetween 2 compounds 2 Na + Cl2 2 NaCl Na Cl Na Cl General form: A + B AB element or element or compound compound compound
Photosynthesis C6 2 + O H2O6 C6H12O6 + O2 6Formation of water 2 H2 + O2 H2O 2Formation of salt 2 Na + Cl2 NaCl 2General Form A + B C
Decomposition reaction: -In a decomposition reaction, a single reactantdecomposes to give 2 or more products. Decompositionreactions requireenergy in the form of heat, light or electricityTypes of decomposition reactions:a. Decomposition reactions which require heat areknown as thermolytic decomposition reactionsb. Decomposition reactions which require light areknown as photolytic decomposition reactionsc. Decomposition reactions which require electricity areknown as electrolytic decomposition reactions
Decomposition reaction 2 H 2O 2 H2 + O2 H O H + H O HGeneral form: AB A + B compound two or more elements or compounds
Hydrogen Peroxide 2 H2O2 H2O2 + O2Electrolysis of water electricity 2 H2O H2 2 + O2Nitrogen triiodide 2 NI3 N2 + I2 3General Form AB A + B
Displacement reaction:-Those reaction in which one elementtakes the place of another element ina compound, are known asdisplacement rection. Single-replacement reaction Mg + CuSO4 MgSO4 + Cu General form: A + BC AC + B
Double displacement reaction:- A chemical reaction in which there is an exchange of ions between the reactants to give new substances is called double displacement reaction Double-replacement reaction CaCO3 + 2 HCl CaCl2 + H2CO3 General form: AB + CD AD + CB
If a substance gains oxygen or loses hydrogenduring a reaction, it is said to be oxidised.
•A substance that loses oxygen or gains hydrogen is known as an oxidising agent.•A substance that loses hydrogen or gainsoxygen is known as a reducingagent. •An oxidising agent gets reduced whereas a reducing agent gets oxidised•The oxidation and reduction reactionare also called redox reaction.
Rancidity can be prevented by:(A) Adding antioxidants i.e. the substances which prevent oxidation (B) Refrigeration (C) Storing the food in air-tight containers