Reactants: substances about to react Products: new substances produced Reactants Products YIELD

Law of Conservation of Mass mass can neither be created nor destroyed in a chemical reaction

Indicators of State  (s) or (cr): solid  ( l ): liquid  (aq): aqueous dissolved in water  (g): gas

Writing Balanced Chemical Equations 1.Describe the reaction in words 2.Rewrite using formulas and symbols (Check for diatomic elements!) 3. Check equation for atom balance 4. Choose coefficients that balance the equation

Types of Chemical Reactions

Synthesis: 2 or more substances combine to form another more complex substance A+B  AB Decomposition: 1 substance breaks down into 2 or more simpler substances AB  A+B

Single Displacement: 1 element replaces another in a compound A + BC  AC + B Cu + Ag(NO3)  Cu(NO3) + Ag

Double Displacement: 2 ionic compounds in solution  Precipitate  Water  Gas AB + CD  AD + CB AgNO3(aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)

Bond Energy  The amount of energy required to put a bond together is equal to the amount it takes to pull them apart.  Bonding to hydrogen atoms together absorbs 436 kj of energy.  When two hydrogen atoms are split how much energy is released?  436 kj

Endothermic Reaction: net absorption of energy  More energy is required to break bonds than to form new ones  Bonds formed have greater potential energy than bonds that were broken  Ex. Ice packs Exothermic Reaction: net release of energy  Less energy is required to break old bonds than to form new ones  Bonds formed have less potential energy than the bonds that were broken  Ex. Hand warmers

Bond Energy and Conservation of Energy  Energy released in an exothermic reaction is NOT CREATED BY THE REACTION!  It was stored as potential energy in the bonds of the reactants  In an endothermic reaction the products store energy as potential energy rather than releasing it as heat.

Activation Energy  Energy that may be needed to start a reation  Used to break the bonds in the reactants

Catalyst:  A catalyst can increase the rate of a chemical reaction  Decreases the activation energy  Decreases costs making rxn more economical  The human body uses enzymes to catalyze reactions

Exploring ad Catalyst: Lab In A Nutshell  The reaction did not take place until the heated copper was added  The copper was not consumed by the reaction  Regains original color  2Cu + O 2  2CUO  CuO + C 2 H 5 OH  C 2 H 4 O + H 2 O + Cu

Read Catalysts for Food Production p