Types of Reactions 7.2

Classifying Reactions reactions are often classified by the type of reactant or the number of reactants and products. some general types of chemical reactions are: synthesis decomposition single-replacement double-replacement combustion

synthesis a synthesis reaction is a reaction in which two or more substances react to form a single substance: Na + Cl ---> NaCl 2H2 + O2 ---> 2H2O

decomposition decomposition is a reaction in which a compound breaks down into two or more simpler substance. The exact opposite of synthesis. 2H2O ---> 2H2 + O2 CaCO3 ---> CaO + CO2

single replacement a single-replacement reaction is a reaction in which one element takes the place of another 2K + 2H2O ---> H2 + 2KOH Cu + 2AgNO3 ---> Cu(NO3)2 + 2Ag

double replacement a double replacement reaction is one in which two different compounds exchange positive ions and form two new compounds: CaCO3 + 2HCL ---> CaCl2 + H2CO Pb(NO3)2 + 2KI ---> PbI2 + 2KNO3

combustion a combustion reaction is one in which a substance reacts rapidly with oxygen, often producing heat and light. CH4 + 2O2 ---> CO2 + 2H2O

Energy Changes in Reactions 7.3

chemical bonds and 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.

breaking and forming bonds breaking chemical bonds requires energy. forming chemical bonds releases energy.

exothermic and endothermic reactions during a chemical reaction, energy is either released or absorbed.

exothermic reactions a chemical reaction that releases energy to its surroundings is called an exothermic reaction. in exothermic reactions, the energy released as the products form is greater than the energy required to break the bonds in the reactants.

Reaction Energy - Exothermic energy released to the surroundings ex: freezing

endothermic reactions a chemical reaction that absorbs energy from its surroundings is called an endothermic reaction. in an endothermic reaction, more energy is required to break the bonds in the reactants than is released by the formation of the products.

Reaction Energy - Endothermic energy is absorbed from the surroundings. ex: melting

conservation of energy in an exothermic reaction, the chemical energy of the reactants is converted into heat plus the chemical energy of the products. in an endothermic reaction, heat plus the chemical energy of the reactants is converted into the chemical energy of the products.