Chemical Reactions How matter changes

What is a chemical reaction? Chemical Reactions occur when there is a CHANGE in the CHEMICAL MAKEUP of a sample Examples of chemical reactions: Burning gasoline Iron oxidizing into rust Baking soda and vinegar Examples of NOT chemical reactions (physical changes): Water boiling and turning into steam Salt dissolving into water Mixing together red paint and blue paint to make purple paint

Identifying a chemical reaction The only sure-fire, 100% accurate way to identify a chemical reaction is to know what CHEMICALS YOU START WITH AND END WITH. If any chemicals changed then it’s a chemical reaction. Examples: C8H18 + O2 → CO2 + H2O Fe + O2 → Fe2O3 CH3COOH + NaHCO3 → CH3COONa + H2O + CO2

Things to Look For (If you don’t know the chemicals) Bubbles of gas form Precipitates (insoluble solids) form Color change Temperature change Light emitted Volume change Conductivity change Melting/boiling point change Smell or taste change (not recommended) Change in any distinctive chemical/physical property

Synthesis Decomposition Single Replacement Double Replacement 5 Types of Reactions Synthesis Decomposition Single Replacement Double Replacement Combustion

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Synthesis Two things coming together A + B  AB + 

Decomposition One thing coming apart AB  A + B  +

AB + C  AC + B Or AB + C  CB + A Single Replacement One part is switched AB + C  AC + B Or AB + C  CB + A

Example +  +  + +

Double Replacement Both things switch AB + CD  AD + CB +  +

Combustion A hydrocarbon burns in oxygen CxHy + O2  CO2 + H2O

Classifying Reactions Identify the following reactions:

The Law of the Conservation of Mass

The Law of the Conservation of Mass Mass cannot be created or destroyed Can be represented in chemical reactions Use coefficients to balance reactions in accordance to the law of the conservation of mass

The Law of the Conservation of Mass

Reactants Products 5 4 3

Practice Keep track of your numbers Both sides must be equal You can only change coefficients!

Stoichiometry Stoichiometry tells the future Uses mole relationships from a balanced chemical equation to predict the amount of reactants needed to produce a certain amount of product. The amount of product calculated from a stoichiometric equation is called the theoretical yield A limiting reactant must be calculated first