Transcript Reaction Rates

UNIT 7-CHEMICAL REACTONS
RATES OF
REACTIONS
Collision Theory
Reaction
rate depends
on the collisions
between reacting
particles.
Successful
collisions occur
if the particles...
collide with each other
have the correct orientation
have enough kinetic energy
to break bonds
Activation Energy
(Ea):
minimum energy
required for a
reaction to occur
Activation Energy
 Low
Ea =
faster
reaction rate
Ea
 High
Ea =
slower
reaction rate
?
EXOTHERMIC
Heat energy
released
2H2(l) + O2(l)  2H2O(g) + energy
ENDOTHERMIC
Heat
energy
absorbed
2Al2O3 + energy  4Al + 3O2
Factors Affecting Rxn Rate
1. Surface Area (SA)
 high SA = fast reaction rate
 more opportunities for
collisions
 Increase surface area by…
- using smaller particles
- dissolving in water
How can you make sugar
cubes dissolve faster?
2. Concentration
high conc. = fast rxn rate
more opportunities for
collisions
3. Temperature
high temp = fast rxn rate
high KE
-fast-moving particles
-more likely to reach
activation energy
Which of these will sugar
dissolve faster in?
4. Catalyst
substance that increases rxn
rate without being consumed
(used up) in the rxn
lowers the activation energy