Chemical reactions
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Chemical Reactions. Chapter 7.2 Notes. Chemical Change. A chemical change occurs when a substance reacts and forms one or more new substances. Signs of a chemical change include color change, temperature change, light produced, gas formed, precipitate formed. Reactions.

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Chemical Reactions

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Chemical reactions

ChemicalReactions

Chapter 7.2 Notes


Chemical change

ChemicalChange

  • A chemical change occurs when a substance reacts and forms one or more new substances.

    • Signs of a chemical change include color change, temperature change, light produced, gas formed, precipitate formed.


Reactions

Reactions

  • Reactions are often classified by the type of reactant or the number of reactants and products.


Types of reactions

Types of Reactions

  • We will be looking at six different types of reactions.

    • Synthesis

    • Decomposition

    • Single replacement

    • Double replacement

    • Combustion

    • Acid-Base


Synthesis

Synthesis

  • Synthesis

    • A reaction in which two or more substances react to form a single substance.

      2H2+ O2 2H2O

  • 2 hydrogen gas molecules react with one oxygen gas molecule to form 2 liquid water molecules.


  • Decompostion

    Decompostion

    • Decomposition

      • A reaction in which a compound breaks down into two or more simpler substances.

        2KClO3 2KCl + 3O2


    Single replacement

    Single Replacement

    • Single Replacement

      • A reaction in which one element takes the place of another element in a compound.

        2Al + 3CuSO4 Al2(SO4)3 + 3Cu


    Double replacement

    Double Replacement

    • Double Replacement

      • A reaction in which two different compounds exchange positive ions and form two new compounds.

        Pb(NO3)2+ 2KI  PbI2 + 2KNO3


    Combustion

    Combustion

    • Combustion

      • A reaction in which a substance reacts rapidly with oxygen, often producing heat and light.

        CH4+ 2O2 CO2 + 2(H2)O


    Acid base

    Acid-Base

    • Acid-Base

      • This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water.


    Acid base1

    Acid-Base

    HBr+ NaOH ---> NaBr + H2O

    • Hydrobromic acid reacts with sodium hydroxide to produce sodium bromide and water.


    Electron transfer reactions

    Electron Transfer Reactions

    • Reactions as Electrons Transfer

      • The discovery of subatomic particles enables scientists to classify certain chemical reactions as transfers of electrons between atoms.


    Oxidation

    Oxidation

    • Oxidation is classified as any process in which an element loses electrons during a chemical reaction.


    Oxidation1

    Oxidation

    • For example, when iron reacts with oxygen to form rust or when calcium reacts with oxygen to form calcium oxide.

      • 2Ca + 02 2CaO

      • Ca Ca2+ + 2e-

        • Even though the reactants and products are balanced, the elements themselves have a charge. In this case, calcium lost two electrons and has a charge of +2.


    Reduction

    Reduction

    • Reduction is the process in which an element gains electrons during a chemical reaction. A reactant is said to be reduced if it gains an electron.

      • For example, in the previous calcium oxide reaction, calcium gave away two electrons and became positive, which is oxidation, however, oxygen gained two electrons and became negative, which is reduction.

        • O + 2e- O2-


    Oxidation reduction

    Oxidation-Reduction

    • Oxidation and reduction always occur together. When one element loses electrons another element must gain electrons.

    • Oxidation-Reduction Reaction

      • An oxidation-reduction reactions is one in which electrons are transferred from one reactant to another.


    Energy changes in reactions

    Energy Changes in Reactions

    Chapter 7.3


    Chemical energy

    Chemical Energy

    • Chemical Energy is the energy stored in the chemical bonds of a substance.

      • Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.


    Types of reactions1

    Types of Reactions

    • During a chemical reaction, energy is either released or absorbed.

      • Exothermic reaction – A reaction in which energy is released into its surroundings

      • Endothermic reaction – A reaction in which energy is absorbed from its surroundings.


    Catalyst

    Catalyst

    • A catalyst is a substance that affects the reaction rate without being used up in the reaction.

      • Chemists use catalysts to speed up a reaction or enable a reaction to occur at a lower temperature.


    Catalysts

    Catalysts

    • Since catalysts are neither reactants or products they are written over the arrow in a chemical equation.

      V2O5

      2SO2+ O2 2SO3


    Conservation of energy

    Conservation of Energy

    • Conservation of Energy

      • In an exothermic reaction, the chemical energy of the reactants is converted into heat plus the chemical energy of the products. While it may appear energy is lost due to heat, it is not. The total amount of energy before and after the reactions is the same.


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