Download REACTION RATES: KINETICS

Bell work
• Which type of organic compound is
essential for providing energy to
organisms?
A. proteins
B. carbohydrates
C. amino acids
D. hydrocarbons
REACTION RATES: KINETICS
• Rate that reactants turn into products
5 FACTORS AFFECTING REACTION RATES
• 1. temperature: incr. temp INCREASES
rxn rates
Why? *particles move faster and collide
with greater intensity
• 2. surface area: increasing will cause
reaction rate to increase
Why? *greater exposure of reacting
particles to each other
examples: pulverizing, crushing, chopping up, etc.
3. agitation: increases reaction rate
Why? *increases likelihood
ofparticles being exposed to one
another; increase in collisions
examples: shaking, stirring
• 4. concentration: increasing concentration of
reactants increases rate
Why? *increasing # particles increases
chance of collision resulting in a reaction
• 5. catalysts: substance that increases the
reaction rate without being used up in the
reaction.
Why? * lowers the ACTIVATION energy;
sort of “invites” reacting particles together
so they will react
Reaction Rates
• It is possible to vary the conditions of the
rxn, the rate of almost any rxn can be
modified
o collision theory can help explain why the
rates can be modified
• Several strategies can be used:
o
o
o
o
Increase the temperature
Increase the concentration
Decrease the particle size
Employ a catalyst
Temperature
• Increasing the temp speeds up the rxn,
while lowering the temp slows down the
rxn
• Increasing the temp increases the
frequency of the collisions
– Collisions taking place more often more
likely they are to stick
• And the extra energy increases the power
of the collisions
– Also increasing the likelihood of a
successful collision
• Just sitting out, charcoal does not react
at a measurable rate
– However, when a starter flame touches the
charcoal, atoms of reactants collide with
higher energy and greater frequency
– Some of the collisions are high enough in
energy that the product CO2 is formed
o
The energy released by the rxn then supplies enough energy to get more C and O2
over the activation-energy barrier
• Evidence
of this would be if you remove
the starter flame, the rxn will continue on
its own.
Concentration
• The more reacting particles you have in a
given volume, the higher the rate of rxn.
• Cramming more particles into a fixed
volume increases the concentration of
reactants,
– Increasing the concentration, increases the
frequency of the collisions, and therefore
increasing the reaction rate.
Particle Size
• The smaller the particle size, the larger
the surface area for a given mass of
particles
• The total surface area of a solid or liquid
reactant has an important effect on the
rate of reaction.
• An increase in surface area increases the
amount of the reactant exposed for
collision to take place…
– Which increases the collision frequency
and the reaction rate.
Particle Size
o
One way to increase the surface area of
solid reactants is to dissolve them
• which
separates the particles and
makes them more accessible to other
reactants.
o
Grinding solids into a fine powder also
increases the surface area of reactants
• Small
dust-like particles can be very
dangerous, can be highly explosive
Catalyst
o
An increase in temp is not always the best
way to increase the rate of rxn
•A
o
catalyst is often better.
A catalyst is a substance that increases
the rate of a rxn without being changed
during the rxn
• They
permit rxns to proceed at lower
energy than is normally required
o
With a lower activation energy more
reactants can form products in a given
amount of time.