1. Factors Affecting Reaction Rates

2. C12-3-07 FACTORS THAT AFFECT RATE
OUTCOME QUESTION(S):
C FACTORS THAT AFFECT RATE
Draw potential energy diagrams for endothermic and exothermic reactions.
Include: heat of reaction (enthalpy)
Identify and explain factors that affect the rate of a chemical reaction.
Include: nature of reactants, surface area,
concentration, pressure, volume, temperature,
and effects of a catalyst.
Vocabulary & Concepts
enzyme inhibitor

3. +
Potential
Energy
Kinetic Energy
Kinetic Energy
Kinetic Energy
EA requirements set the stage for reaction rate, but there are things that can be done to increase it

4. 1. Effect of Particle Size (surface area)
Rate of reaction increases with increased surface area (crushing, grinding) .
This is one that is often messed up: making things smaller increases the exposed surface area
More particles involved, more frequent collisions, higher chances of successful collisions.

5. 2. Effect of Concentration
Rate of reaction increases with increased concentration (mol/L) of particles.
More particles involved, more frequent collisions, higher chances of successful collisions.

6. Note: pressure changes volume which affects concentration:
3. Effect of Pressure
Only affects reaction rates of gaseous reactions.
Rate of reaction increases with decreased volume of the container - mimics higher [ ].
Note: pressure changes volume which affects concentration:
8 “moles” = 4 M
2 L
8 “moles” = 8 M
1 L
8 “moles” = 16 M
0.5 L
Closer particles, more frequent collisions, higher chances of successful collisions.

7. 4. Effects of a Temperature Change
Rate of reaction increases with increased temperature.
Agitation is an easy way to give extra (temperature) kinetic energy
More kinetic energy, more particles with EA,
higher chances of successful collisions.

8. 5. Effect of the Nature of Reactants
Reactions with fewer compounds react faster
2 NO(g) + O2(g) → 2 NO2(g)
2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)
Aqueous (aq) reactions are fastest: > g > l > s
weaker IMFs and more surface area
H2(g) + I2(g) → 2 HI(g)
KNO3(aq) + NaI(aq) → KI(aq) + 2 NaNO3(aq)
And…some compounds simply react faster just because of the nature of the atoms that compose them

9. 6. Effect of Catalysts
A catalyst speeds up a reaction by providing an alternate pathway with a lower EA
Does not alter products or ΔH
Appears unchanged over course of the reaction
Not shown in the chemical reaction equation
Enzymes are known as biological catalysts.
An inhibitor is the opposite of a catalyst.
A catalyst would be a flashlight used to unlock a door in the dark – the key did the work, the flashlight provided an alternate pathway for a quicker result

10. Catalysts create a pathway of lower activation energy for both the forward and reverse reactions

11. Things that increase reaction rate:
increase surface area
increase concentration
increase pressure
increase temperature
aqueous or gas phases
catalyst
To decrease reaction rate - do the opposite....

12. C12-3-07 FACTORS THAT AFFECT RATE
CAN YOU / HAVE YOU?
C FACTORS THAT AFFECT RATE
Draw potential energy diagrams for endothermic and exothermic reactions.
Include: heat of reaction (enthalpy)
Identify and explain factors that affect the rate of a chemical reaction.
Include: nature of reactants, surface area,
concentration, pressure, volume, temperature,
and effects of a catalyst.
Vocabulary & Concepts
enzyme inhibitor