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