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Chemical Reactions 1 or more substances changed into a new substance or substances. YIELD. Reactants: substances about to react Products: new substances produced Reactants Products. Law of Conservation of Mass. - PowerPoint PPT Presentation
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Reactants: substances about to react
Products: new substances produced
Reactants Products
YIELD
Law of Conservation of Massmass 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 + BCu + 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 + O2 2CUO
CuO + C2H5OH C2H4O + H2O + Cu
Read Catalysts for Food Productionp. 319- 321