X chemistry full notes chapter 1
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    X chemistry full notes chapter 1 X chemistry full notes chapter 1 Document Transcript

    • Chemical reactions and equationsTop definitions:1. Chemical reaction: A chemical reaction involves achemical change in which substances react to form newsubstances with entirely new properties. Substances thatreact or take part in the reaction are known as reactants andthe substances formed are known as products.2. Physical change: If a change involves change in colour orstate but no new substance is formed, then it is a physicalchange.3. Chemical change: If a change involves formation of newsubstances, it is a chemical change.4. Chemical equation: The symbolic representation of achemical reaction is called a chemical equation.5. Exothermic and endothermic reactions: If heat is evolvedduring a reaction, then such a reaction is known asexothermic reaction. If heat is absorbed from thesurroundings, then such a reaction is known as endothermicreaction6. Combination reaction: Combination reaction is a reactionin which 2 or more substances combine to give a singleproduct.7. Decomposition reaction: In a decomposition reaction, asingle reactant decomposes to give 2 or more products.Decomposition reactions require energy in the form of heat,light or electricity8. Displacement reaction: A reaction in which a more activeelement displaces less active element from its salt solution.For More School Notes & Projects Visit www.toppersarena.com
    • 9. Reactivity series: The Reactivity series is a list of metalsarranged in the order of decreasing reactivity. The mostreactive metal is placed at the top and the least reactivemetal is placed at the bottom.10.Double displacement reaction: A chemical reaction inwhich there is an exchange of ions between the reactants togive new substances is called a double displacementreaction.11.Precipitation reaction: An insoluble solid known asprecipitate is formed during a double displacement reaction.Such reactions are also known as precipitation reactions.12.Redox reaction: A reaction, in which oxidation andreduction takes place simultaneously is known as redoxreaction.13.Oxidation: Oxidation is a chemical process in which asubstance gains oxygen or loses hydrogen.14.Reduction: Reduction is a chemical process in which asubstance gains hydrogen or loses oxygen.Key learning:1. A chemical reaction involves a chemical change in whichsubstances react to form new substances with entirely newproperties. Substances that react or take part in the reactionare known as reactants and the substances formed areknown as products.2. During a chemical reaction, there is a breaking of bondsbetween atoms of the reacting molecules to give products.3. A chemical reaction can be observed with the help of anyof the following observations:a) Evolution of a gasFor More School Notes & Projects Visit www.toppersarena.com
    • b) Change in temperaturec) Formation of a precipitated) Change in coloure) Change of state4. Physical change: If a change involves change in colour orstate but no new substance is formed, then it is a physicalchange.5. Chemical change: If a change involves formation of newsubstances, it is a chemical change.6. Exothermic and endothermic reactions: If heat is evolvedduring a reaction, then such a reaction is known asExothermic reaction. If heat is absorbed from thesurroundings, then such a reaction is known as endothermicreaction.7. Chemical equation: The symbolic representation of achemical reaction is called a chemical equation.8. Features of a chemical equation:a. The reactants are written on the left hand side with a plussign between them.b. The products are written on the right hand side with aplus sign between them.c. An arrow separates the reactants from the products. Thearrow head points towards the products and indicates thedirection of the reaction.9. Skeletal chemical equation: A chemical equation whichsimply represents the symbols and formulae of reactantsand products taking part in the reaction is known as skeletalchemical equation for a reaction. For example: For theburning of Magnesium in the air, Mg + O2  MgO is theskeletal equation.For More School Notes & Projects Visit www.toppersarena.com
    • 10. Balanced chemical equation: A balanced equation is achemical equation in which number of atoms of eachelement is equal on both sides of the equation i.e. numberof atoms of an element on reactant side = number of atomsof that element on the product side.11. As per the law of conservation of mass, the total massof the elements present in the products of a chemicalreaction is equal to the total mass of the elements present inthe reactants.12. The process of equating the number of atoms on boththe sides of a chemical equation is known as balancing of achemical equation.a. The first step in balancing a chemical equation is to writethe number of atoms of each element present on the lefthand side and right hand side.b. We should always start balancing with the compound thatcontains maximum number of atoms. It can be reactant or aproduct. Then in that compound select the element whichhas the maximum number of atoms.c. While balancing a chemical equation, the molecularformulae of the reactants and products should not change.The molecular formulae are simply multiplied by suitablecoefficients.d. To make a chemical equation more informative, thereaction conditions such as temperature, pressure orcatalyst are written on the arrow separating the reactantsand products.e. The evolution of gas is indicated by an upward arrow.f. The formation of precipitate is indicated by a downwardarrow.g. Heat evolved during the reaction is written as + Heat onthe product side.h. Heat absorbed during the reaction is written as + Heat onthe reactant side.13.Types of chemical reactions:For More School Notes & Projects Visit www.toppersarena.com
    • a. Combination reactionb. Decomposition reactionc. Displacement reactiond. Redox reaction14.Combination reaction is a reaction in which 2 or moresubstances combine to give a single product. Combinationreaction can be between 2 elements, between an elementand a compound or between 2 compounds.15.Decomposition reaction: In a decomposition reaction, asingle reactant decomposes to give 2 or more products.Decomposition reactions require energy in the form of heat,light or electricity16.Types of decomposition reactions:a. Decomposition reactions which require heat are known asthermolytic decomposition reactionsb. Decomposition reactions which require light are known asphotolytic decomposition reactionsc. Decomposition reactions which require electricity areknown as electrolytic decomposition reactions17.Displacement reaction: A reaction in which a more activeelement displaces less active element from its salt solution.18.The reactivity series is a list of metals arranged in theorder of decreasing reactivity. The most reactive metal isplaced at the top and the least reactive metal is placed atthe bottom.19.Double displacement reaction: A chemical reaction inwhich there is an exchange of ions between the reactants togive new substances is called double displacement reaction.For More School Notes & Projects Visit www.toppersarena.com
    • 20.Precipitation reaction: An insoluble solid known asprecipitate is formed during a double displacement reaction.Such reactions are also known as precipitation reactions.21.Redox reaction: A reaction in which oxidation andreduction take place simultaneously in a reaction, is knownas a redox reaction.22.Oxidation is a chemical process in which a substancegains oxygen or loses hydrogen.23.Reduction is a chemical process in which a substancegains hydrogen or loses oxygen.24.If a substance gains oxygen or loses hydrogen during areaction, it is said to be oxidised.25.If a substance gains hydrogen or loses oxygen during areaction, it is said to be reduced.26.A substance that loses oxygen or gains hydrogen isknown as an oxidising agent.27.A substance that loses hydrogen or gains oxygen isknown as a reducing agent.28.An oxidising agent gets reduced whereas a reducingagent gets oxidised.29. In terms of electronic concept, Oxidation is defined as aloss of electrons while reduction is defined as a gain ofelectrons.30. Corrosion is the slow eating up of metals by the actionof air and moisture on their surfaces. Corrosion in case ofIron is known as Rusting.31. Chemically, rust is hydrated ferric oxide (Fe2O3.xH2O)For More School Notes & Projects Visit www.toppersarena.com
    • 32. Advantages of corrosion: Though corrosion isundesirable, it can be advantageous in case of aluminiumwhich on exposure to air, gets coated with a protective layerof aluminium oxide. This protects the metal underneath fromfurther corrosion and damage.33.Rancidity: When oils and fats or foods containing oils andfats are exposed to air, they get oxidised due to which thefood becomes stale and gives a bad taste or smell. This iscalled Rancidity.34. Rancidity can be prevented by:a) Adding antioxidants i.e. the substances which preventoxidationb) Refrigerationc) Storing the food in air-tight containersFor More School Notes & Projects Visit www.toppersarena.com