Chemical Reactions

Chemical Reactions When 2 or more elements chemically combine to form a “new” substance

Symbols: + used to separate 2 reactants or 2 products  yields; used to separate reactant & product (s) solid (l) liquid (g) gas (aq) aqueous; dissolved in water  catalyst= substance that speeds up a reaction but is NOT used up in the reaction

Chemical Equation Is a representation of a chemical reaction Two Parts Reactants Products

The arrow () divides an equation in half Reactants vs Products C + O2  CO2 The arrow () divides an equation in half Reactants The substance(s) that undergo the change All things on the left side of the “” Ex: C & O2 Products The new substance(s) that form All things on the right side of the “” Ex: CO2

Id the Reactants and Products 2Cu + O2  2CuO 2KClO3  2KCl + 3O2 HCl + NaOH  NaCl + H2O N2H4 + O2  N2 + 2H2O

Endothermic vs Exothermic Reaction absorbs energy from its surrounding Surrounding becomes colder Exothermic Reaction releases energy to the surrounding Surrounding becomes warmer

Signs of a Reaction Production of a GAS Formation of a Precipitate Fizzing, bubbling Formation of a Precipitate Insoluble solid Energy is released Light, heat Color Change

Counting Atoms Number in front is called a coefficient Coefficients are multiplied to all elements behind it Subscripts go to what they just follow

Counting Atoms Practice Mg(OH)2 3Ca(NO3)2 NH4OH

How Do I Balance an Equation? Id the elements present Count the amount of atoms on both sides of the “” for each element Place coefficients in front of compounds and multiply to any subscript Recount the atoms to see if they are equal

____Cu + ____O2  ____CuO Balancing Practice #1 ____Cu + ____O2  ____CuO

____N2H4 + ____O2  ____N2 + ____H2O Balancing Practice #2 ____N2H4 + ____O2  ____N2 + ____H2O

____KClO3  ____KCl + ____O2 Balancing Practice #3 ____KClO3  ____KCl + ____O2

Types of Reactions 4 Main Types 2 Special Types Synthesis Decomposition Single Replacement Double Replacement 2 Special Types Combustion Reaction Neutralization Reaction

Synthesis Reaction A + B  AB When 2 or more substances react to form a single substance 21 Dating: Becoming a Couple

Decomposition Reaction AB  A + B When a compound breaks down into two or more substances 12 Dating: Breaking Up

Single Replacement Reaction A + BC  B + AC A reaction in which one element trades places with another element in a compound Element and Compound  Dating: CHEATING

Double Replacement Reaction AB + CD  AD + BD Where two different compounds exchange positive ions (cations) to form two new compounds All compounds (4 of them) Dating: Swingers

Type Of Reaction Practice Na3PO4 + 3KOH  3NaOH + K3PO4 P4 + 3O2  2P2O3 Pb + FeSO4  PbSO4 + Fe CaCO3  CaO + CO2

Special Reaction: Combustion Reaction When an element or compound reacts with oxygen producing energy in the form of heat and/or light Reactants are always hydrocarbon & O2 Products are always CO2 & H2O Ex: CH4 + 2O2  CO2 + H2O

Reactions in Aqueous Solutions Aqueous= dissolved in water Over 70% of Earth’s surface is covered in water About 66% of the human body is water It is not surprising that many important chemical reactions take place in water.

Reactions in Aqueous Solutions continue… Complete ionic equation = shows dissolved ionic compounds as dissociated free ions. Spector ions = appears on both sides of an equation and is not directly involved in the reaction Net ionic equation = shows only the particles that are directly involved in the chemical change