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What makes “superglue” bond instantly while PVA glue does not? - PowerPoint PPT Presentation


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What makes “superglue” bond instantly while PVA glue does not? What factors determine how quickly food spoils? Why do “glow sticks” last longer when stored in the freezer?. Rates of reaction Rate = change in concentration (of reactant or product) time. Methods for measuring rate of reaction.

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Presentation Transcript
slide1

What makes “superglue” bond instantly while PVA glue does not?

  • What factors determine how quickly food spoils?
  • Why do “glow sticks” last longer when stored in the freezer?
methods for measuring rate of reaction

Methods for measuring rate of reaction

150g

Collect a gas over time

Follow a change in mass over time

Formation of a precipitate or colour change over time.

f actors affecting rate
Factors affecting rate
  • Concentration (pressure with gases)
  • Temperature
  • Catalysts
  • Surface Area
in contact
In Contact
  • Reactions don’t happen unless the substances are in contact.
slide7
Why?
  • The particles of the reactants need to get together so that they can react.
how does that work then
How does that work then?

Reactant particles

collide

REACTION

Product particles

formed

is it really that simple
Is it really that simple?

Yes

Well, sort of.

not really.

OK, not quite!

not all collisions are effective
Not all collisions are effective
  • Paper burns
  • Paper + oxygen  carbon dioxide + water + nitrogen
  • The paper in this room isn’t burning.
  • It doesn’t have enough energy to burn.
  • If we make it hotter it will catch fire.
  • Paper burns on its own at 250 ºC
a collision but with no effect
A collision but with no effect

Reactant particles

collide

Product particles

not formed as there is not enough energy

activation energy
Reactions only happen if the particles have enough energy.

The minimum amount of energy needed to start a reaction is called the Activation Energy

The amount of activation energy needed is different for each reaction.

But

Every reaction has activation energy, they all need a little push to get started.

Activation Energy
more than the activation energy
More than the activation energy.

Reactant particles

collide

REACTION

Product particles

formed

more than the activation energy1

O

O

O

C

O

More than the activation energy.

C

Effective collisions, a reaction.

the collision theory
The Collision Theory
  • Particles are constantly moving
  • For a chemical reaction to take place the reactant particles must collide first
  • For the collision to be successful the particles must have the right amount of energy
  • The minimum amount of energy required for an effective collision is called the activation energy
slide16

Successful collisionsWhen two molecules collide a reaction might take place if:- The molecules have enough energy to overcome the activation energy- The molecules collide in the correct orientation

c oncentration
Concentration
  • More particles in the same volume means they are closer together so greater chance of colliding.
  • More collisions means more collisions with energy greater than activation energy.
  • More frequent successful collisions means increased rate of reaction.
p ressure
Pressure
  • When the pressure is increased the same number of molecules occupy a smaller volume
  • For gaseous reactants this has the same effect as increasing the concentration.
  • More collisions take place, so more collisions with energy greater than activation energy.
  • More frequent successful collisions means increased rate of reaction.
catalysts

Catalysts

A catalyst speeds up a reaction without being consumed by the overall reaction.

c atalysts
Catalysts
  • Catalysts reduce the activation energy needed for a reaction
  • They do this by offering an alternate route for the reaction to take (for example via an intermediate)
  • Lower activation energy means more successful collisions
  • More successful collisions means faster rate
slide21

Catalysts are very useful in industry

  • They often require lower temperatures than uncatalysed reactions, which reduces the energy demand and carbon dioxide emissions from fossil fuels.
  • They allow different reactions to be used with a better atom economy and reduced waste.
  • They are often enzymes which allow processes to operate at lower temperatures and pressures
slide22

Examples of economically important catalystsIron in ammonia productionZiegler– Natta catalyst in poly(ethene) productionPlatinum/palladium/rhodium in catalytic converters