Chemical Reactions

Chemical Reactions and Equations A chemical reaction occurs when the atoms of one or more substances are rearranged to form completely new substances

Evidence for Chemical Reactions When a chemical reaction occurs there are typically several signs that a chemical change is happening Color change Solid is formed from two liquids Heat is given off Light is given off

Representing Chemical Reactions In every chemical reaction there are reactants and products Reactants are the starting materials Products are the new compounds that are formed Reactant1 + Reactant2 Product1 + Product2

Chemical Equations contd. In chemical equations, chemical symbols or formulas are used to show which elements or compounds are participating in the reaction Examples: NaOH + HCl  NaCl + H2O AgNO3 + HCl  AgCl + HNO3 Mg + O2  MgO

Balancing Chemical Equations Let's take a look at our previous reactions: NaOH + HCl  NaCl + H2O AgNO3 + HCl  AgCl + HNO3 Mg + O2  MgO According to the law of conservation of mass, mass can neither be created nor destroyed, therefore we must balance the equation to show this

Types of Chemical Reactions

Single Replacement Single replacement reactions occur when a single element reacts with a compound One element replaces another to form a new compound Example: Mg + 2 HCl  MgCl2 + H2

Double Replacement Double replacement reactions occur when two compounds react The ions in each compound simply swap places with each other Example: CaCl2 + Na2CO3  CaCO3 + 2 NaCl

Combustion Combustion reactions occur when one of the reactants is oxygen. Oxygen (O2) has to be a reactant and not a product Example: C3H8 + 5 O2  3 CO2 + 4 H2O

Synthesis Synthesis reactions occur when two or more reactants react to create only one product Example: 2 Na + Cl2  2 NaCl

Decomposition Decomposition reactions occur when one reactant reacts to form two or more products. These are basically the opposite of a synthesis reaction Example: 2 NaClO3  2 NaCl + 3 O2