DESCRIBING CHEMICAL REACTIONS

WHAT ARE CHEMICAL REACTIONS?  Chemical reactions occurs when one or more substances change into one or more different substances.  Chemical reactions obey the law of conservation of mass and can be represented by balanced chemical equations.  Chemical reactions occur in our daily lives and affect us and our environment

Chemical Reactions With Equations  Just like math, chemists use equations to describe chemical reactions.  There are 2 types:  WORD EQUATIONS  CHEMICAL EQUATIONS

WORD EQUATIONS  We write the names for the chemicals involved in the reaction to describe it  Ex.Magnesium + Oxygen  Magnesium Oxide

CHEMICAL EQUATIONS  We use chemical formulas to describe the reactions  Ex. 2 Mg (s) + O 2 (g)  2 Mg 2 O (s)

COMPONENTS OF A REACTION REACTANTS  PRODUCTS Reactant: a chemical present at the start of a chemical reaction that is used up during the reaction Product: a chemical that is produced during a chemical reaction Energy: in some reactions, energy is released (exothermic) while in others energy must be added (endothermic); if energy is put into a reaction, it will be noted on the reactant side and if it is emitted from a reaction it is placed on the products side Catalyst: a substance that causes or accelerates a chemical reaction without itself being affected.

SYMBOLS in REACTIONS   is read as YIELDS, FORMS, PRODUCES  + is used when there are several reactants and/or products involved  State Symbols – solid = (s), liquid = (l), gas = (g), aqueous = (aq)  Remember, aqueous means DISSOLVED IN WATER  If heat is added (endothermic) or produced (exothermic) we use the symbol, Δ = heat/energy  If we use a catalyst to speed up a reaction, we use the symbol