Chemical formulas and Equations Rates of Chemical Reactions.
-
Upload
phyllis-mccarthy -
Category
Documents
-
view
215 -
download
0
Transcript of Chemical formulas and Equations Rates of Chemical Reactions.
Chemical formulas and Equations
Rates of Chemical Reactions
Chemical Formulas and EquationsPhysical Change
Changes that only affect its physical properties like size, shape, or whether it is a solid, liquid or gas
There is no change of materialYou still have the same substance that you began
withIe: crumple paper, cut up wood, changes of water
from ice, to liquid to a gas
Chemical Formulas and Equations
Chemical ChangeA change that produces a new substance with
properties different from those of the original substances
Things that show that a chemical reaction has occurredPrecipitate forms (when 2 liquids combine the
new substance will drop out of solution..is not soluble)
Odor given offChange of colorTemperature change
Chemical Formulas and Equations
Chemical reaction occurs when a chemical change takes place
Anytime you have a new substance formedBurning paper is a result of a chemical
reactionFolding paper is a result of a physical change
because you still have paper, only change of shape
Chemical EquationsUsing chemical symbols of elements and
chemical formula you can write a shorthand of a chemical reaction
The substances you begin with in a chemical reaction is called the reactants
The new substances that are formed is called the product
In a chemical reaction you can write the reactants and resulting products in a chemical equation using arrows (and is read as produces)
Chemical EquationsBaking soda + vinegar gas + white solid
2NaHCO3 + H4C2O2 2NaH3C2O2 + H2O + CO2
Sodium hydroxide plus Sulfuric acid produces sodium sulfate and water
2NaOH + H2SO4 Na2SO4 + H2O
Conservation of MassAntoine Lavoisier: mass of the product must
be the same as the mass of the reactants
Chemical equations must show that there is the same kind and number of atoms that you began with as was formed
Every atom that appears on the reactant side of the equation is found on the product side
Balancing EquationsChemical equations must show the conservation
of mass by having same kind and same numbers of atoms on both side of a chemical reaction
Ag + H2S Ag2S + H2
(Silver tarnishes in presence of sulfur)Notice that the number of atoms aren’t the
same on both sideNeed to count the atoms… you can’t change the
formula but you can add a coefficient in front of the formula to balance equations
Balancing EquationsAg + H2S Ag2S + H2
Notice there is 2 Ag’s on product side and only one on reactant side…. Add a coefficient of 2 in front of reactant silver
2Ag + H2S Ag2S + H2
2 Ag’s, 2 H’s and 1 SIt is balanced
Balancing Equations
Al + O2 Al2O3
Aluminum and oxygen produces aluminum oxide
Not balanced (can only change the coefficient)
4Al + 3O2 2Al2SO3
Balancing Equationshttp://education.jlab.org/elementbalancing/index.html
Energy in Chemical Reactions
Energy releasedHeat, light, sound or other energy is given offWhen bonds break in a chemical reaction new
bonds form in the products and energy is given off
Energy found on product side of chemical reaction
Called an exothermic reaction
2H2 + O2 2H2O + energy
Energy in Chemical Reactions
Energy is AbsorbedEnergy is required to form new productsCan absorb light, sound, heat Called an endothermic reactionEnergy is placed on the reactant side of equations
2H2O + energy 2H2 + O2
Ice packs are example of endothermic reactions
Rates of Chemical reactionActivation Energy: starting a reactionTo start a chemical reaction a minimum
amount of energy is required to begin the process
That energy required is its activation energyFor gasoline to burn energy needs to be
introduced to begin the chemical reaction…. That energy (match) will begin the chemical process
Reaction RateRate refers to a change over timeReaction rate refers to the speed at which
chemical reactions takes place over timeReactions rates in some industries is important
because the faster the rate, the less the costSome faster reaction rates can hurt industries
Ripening fruit gives less time from field to marketsThe slower the ripening rate increases the time it
can be on shelves
Reaction RateTemperature changes rate
Lowering the temperature slows down reaction rates
Meat in freezers, bacteria grows faster in higher temperatures, lower movement of molecules, less chance of causing chemical changes
Temperature affects RateMost chemical reactions speed up with increase
in temperature because of faster moving molecules
Lowering temperature usually slows down reaction rate
Reaction RateConcentration Affects RateCloser the reactant atoms and molecules to
each other, the greater the chance of collisions between them and faster the reaction rate
Amount of substance present in a certain volume is called the concentration of that substance
Increasing the concentrations increases the number of particles of a substance per unit of volume
Reaction RateSurface Area Affects RateIf you increase the surface area you
will increase its chance of reacting with other substancesTwigs broken up compared to logs to
begin a fireCrushing up materials into smaller
pieces increases surface area
Slowing down ReactionsInhibitors slow down chemical
reactions
Makes the process of chemical change longer
BHT on cereal packages slow down the spoilage of cereal and increase its shelf life
Speeding up ReactionsCatalysts are substances that speed up a
chemical reaction without entering into the chemical reactionsIt produces the same amount of product fasterCatalytic Converters utilize metals (platinum) to
produce CO2 and water , which is less harmful in cars fuel combustion.
Enzymes are catalysts that are large protein molecules that speed up reactions needed in cells to work properlyThey help speed up conversion of food to fuel,
build bone and muscle tissue, and converting energy by fitting structures together properly so that reactions can occur faster
Speeding up ReactionsProteases is a special type of enzyme that helps break down large protein moleculesMeat tenderizersContact lenses cleaning solutions
breaks down protein from your eyes that collect on your lenses and cloud your view