Chemical Reactions. Chemical Equation Describes what you had before and then after the change...
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Transcript of Chemical Reactions. Chemical Equation Describes what you had before and then after the change...
Chemical Reactions
Chemical EquationDescribes what you had before
and then after the changeReactants: substances that
undergo changeProducts: new substances
formed
Reactants Products
Chemical EquationChemical equation:
representation of a chemical reaction in which the reactants and products are expressed as formulas
Examples:
C + O2 CO2
Conservation of MassAntoine Lavoisier 1743-1794
◦Law of conservation of mass: mass is neither created nor destroyed in a chemical reaction
Mass of the products is always equal to the mass of the reactants
Balancing Equations
H2 + O2 H2O
NOT BALANCED!
Number of atoms on the reactant side MUST equal the number of atoms on the product side!!!
Balancing Equations
H2 + O2 H2O
Use Coefficients to balance equations
2H2 + O2 2H2O
ExampleCu + O2 CuO
Balanced or unbalanced???
ExamplesNa + Cl2 NaCl
H2 + Cl2 HCl
AgNO3 + Cu Cu(NO3)2 + Ag
BaS + PtF2 BaF2 + PtS
Types of Reactions
Classifying reactionsReactions are often classified by
the type of reactant or the number of reactants and products
General types include:◦Synthesis reaction◦Decomposition reaction◦Single-replacement◦Double-replacement◦Combustion
SynthesisTwo or more substances react to
form a single substance
A + B AB
Example: 2Cu + O2 2CuO
DecompositionCompound breaks down into two
or more simpler substances
AB A + B
Example:CaCO3 CaO +
CO2
Single ReplacementOne element takes the place of
another element in a compound
A + BC B + AC
Example:Cu + 2AgNO3 2Ag +
Cu(NO3)2
Double ReplacementTwo different compounds exchange
positive ions and form two new compounds
AB + CD AD + CB
Example:CaCO3 + 2HCl CaCl2 + H2CO3
CombustionSubstance reacts rapidly with
oxygen, often producing heat and light
Breaking and Forming BondsBreaking bonds:
◦Requires energy Example: Propane grills have a starter
that produces a spark
Forming bonds:◦Releases energy
Example: heat and light are given off by a propane grill
Exothermic ReactionChemical reaction that releases
energy to its surroundings
Endothermic ReactionChemical reaction that absorbs
energy from its surroundings
Exothermic vs EndothermicExo:
◦Reactants have more energy than products AB+ CD+ 450 J AD + CB
Endo: ◦Products have more energy than
reactants AB + CD AD + CB + 450 J
Reaction Rates
Reactions over timeAny change that happens over a
period of time can be expressed as a rate
Reaction rate: rate at which reactants change into products over time◦Tell us how fast a reaction is going
How fast reactants are being consumed How fast the products are being formed How fast energy is being absorbed or
released
Factors Affecting Reaction RatesReaction rate depends on how
often particles collide◦More frequent = increase reaction rate◦Less frequent = decrease reaction rate
TemperatureSurface areaConcentrationStirringCatalysts
TemperatureIncrease in temperature =
increase in reaction rateDecrease in temperature =
decrease in reaction rate
Surface AreaAn increase in surface area
increases the exposure of reactants to one another
An increase in surface area = increase in reaction rate
StirringStirring causes collisions to occur
more rapidlyStirring = increase in reaction
rate
ConcentrationConcentration = number of
particles in a given volumeGreater the concentration =
increase in reaction rate
CatalystsCatalyst: substance that affects
the reaction rate without being used up in the reaction◦Used to speed up reactions or used
to enable a reaction at a lower temperature
◦Written over the arrow because it is not used up
2SO2 + O2 2SO3
V2O3
CatalystsIn order for a reaction to occur,
particles must collide with enough energy to break the bond◦Catalyst lowers this energy barrier◦Provides a surface area for reacting
particles to come together