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Article analysis IVMolarity PacketMolarity by Dilution WSReview

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Chem MattersChem MattersChem Matters Articles by Topic

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Quest for a clean drinkSalting RoadsForensics of Blood

EquilibriumEquilibriumBig name-- easy idea!Big name-- easy idea!

Chemical ReactionsChemical Reactions• You have a system made up of a

bunch of molecules.• Energy is absorbed to break bonds.• Molecules combine to form new

compounds (releasing energy).

Collision TheoryCollision TheoryMolecules must bang together—

with enough energy (activation energy)

in the right orientation (just the right way)

for a reaction to occur

Potential Energy DiagramPotential Energy DiagramEa = activation

energy. This is the minimum amount of energy necessary to make the reaction happen.

Top of the hillActivated complex-

(transition state)

Reverse ReactionsReverse Reactions• Once you have a bunch of the new

compound ………the new compound wants to go back to being the old compound.

In short- the products become reactants In short- the products become reactants and have to find a way to get back up and have to find a way to get back up

over the hillover the hill

Put those two ideas together and you have Put those two ideas together and you have EQUILIBRIUMEQUILIBRIUM

1. Reactants combine to make a products.

2. Products like to break apart and turn back into the reactants.

3. There is a point where the two reactions happen and you can't tell that any reactions are occurring (equilibrium).

Think about a swimming pool.Think about a swimming pool.(Phase Changes)(Phase Changes)

What happens in the summer when it is really hot?

What happens when it is raining?

What is happening when the level of the water doesn’t change?

In a closed system…In a closed system…

1. Net transfer of molecules from the liquid state to the vapor state

2. The amount of the substance in the vapor state becomes constant

3. The equilibrium state is achieved.

Rate of ReactionRate of ReactionDepends on the properties of the

reactants (size and reactivity)

Depends on the conditions of the system

Factors affecting Reaction RateFactors affecting Reaction RateWrite about how each affects the kineticWrite about how each affects the kinetic

energy of the reactants. energy of the reactants.

1. Temperature

2. Concentration

3. Particle Size (surface area)

4. Agitation

Iodine/ Vit C demoIodine/ Vit C demo

Particle Size DemoParticle Size Demo

So.. So.. What exactly is equal at What exactly is equal at equilibrium??equilibrium??

Rateforward rxn = Ratereverse rxn

Law of Chemical Equilibrium

There is no net change in the actual amount of the compounds.

Be careful!! The rate is equal– the amount is probably not equal!!

Changes with time in the Changes with time in the rates of reactions.rates of reactions.

This looks the same no matter what the products and reactants are!!

Equilibrium PositionEquilibrium PositionThe equilibrium position indicates the relative

concentration of the products and reactants at equilibrium.

A + B -----> AB

Can also be the reverse reaction.

AB -----> A + B

We draw a wacky double arrow shows to show what side of the equation is favored (has more).

A + B ABSize Matters!!

LeChatelier’s PrincipleLeChatelier’s Principle If a change is imposed on a system at

equilibrium, the position of the equilibrium will shift in a direction will reduce the change.

Things we can mess with--Things we can mess with--Concentration- if a component is added to a

reaction system at equilibrium, the equilibrium position will shift in the direction that lowers the concentration of that component. If a component is removed, the opposite happens.

H2 + F2 ------> 2HF Add this ------- get more of this

get more of this ------- Add this

TemperatureTemperatureTreat energy as a reactant in an

endothermic reaction and a product in an exothermic reaction.

Predict the direction of the shift in the same

way as when an actual product or reactant is added.

2H2 + O2 2H2O + 483kJ

Pressure-Pressure- only matters with only matters with gasses!gasses!

2SO2(g) + O2(g) 2SO3(g)

VolumeVolumeHow about changing the volume of the

container??

Decreasing the volume of the reaction container will cause the equilibrium to shift towards the side of the reaction with the fewest number of gas molecules.

DemoDemo

Equilibrium ConstantEquilibrium Constant

Equilibrium Expression: Is a ratio of the rates of

reaction.

aA + bB <-- > cC + dD

Keq = [C]c [D]d or [Products][A]a [B]b [Reactants]

State of Matter– State of Matter– does matterdoes matter

Reactants or products that are solids (s) or liquids (l)

are not put into the equilibrium expression

ONLY gasses (g) and aqueous solns (aq)

Are included in the equilibrium expression!!

Let’s Practice!Let’s Practice!Write the equilibrium expression for

the following reactions.

a. H2 + F2 <------> 2HF

b. N2 + 3H2 <-------> 2NH3

AnswersAnswersa. H2 + F2 <------> 2HF

Keq = [HF]2

[H2] [F2]

b. N2 + 3H2 <-------> 2NH3

Keq = [NH3]2

[N2] [H2]3

Example- Write the Example- Write the equilibrium expressionequilibrium expression

CaCO3 (s) + Heat - CaO (l) + CO2(g)

What does KWhat does Keqeq tell us?? tell us??

It tells us which side of the equation is favored (will we get more products or reactants?).

Keq>1 Products favored, Spontaneous

Keq<1 Reactants favored, Nonspontaneous

Here- watch this!!Here- watch this!!http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/066_LeChateliersPr.MOV