Download Factors that affect the rate of reactions

Chapter 6 - Chemical Reactions
Factors Affecting the Rate of Reactions
The rate of a reaction is the measure of how fast the reactants can change into products.
If the reaction takes a long time then it has a LOW reaction rate. If the reaction goes quickly
it has a HIGH reaction rate.
There are 4 different ways in INCREASE the reaction rate.
1. Temperature
Increasing the temp cause the reactants to move faster. If the reactants move faster they will
hit each other more often and with a greater energy this will help them have a successful reaction.
If the temperature is decreased, then the particles will move slower and hit with less often
with less energy.
Higher temp = faster reaction rate
Lower temp = slow reaction rate
2. Concentration
Concentration refers to the amount of reactants that are present in a certain area.
If the concentration of reactants are increased then there are more reactants in the certain
area, therefore the reactants have a better chance of hitting each other and having a
reaction.
If the concentration of reactants are decreased then there are less reactants in a certain
area. This will decrease the chance of the reactants hitting each other and the reaction rate
will slow down.
Concentration ONLY affects reactants in a aqueous or gas phase. It does not help a liquid or
a solid.
low conc. both
low chance
of collision
(slow reaction)
high conc. blue
low conc. red
high conc. both
higher chance
of collision
(faster reaction)
very high chance
of collision
(much faster reaction)
3. Surface Area
Surface area is a measure of how much area is exposed. If the surface area is large, then there
is a better chance of hitting another reactant so the reaction rate will be high.
The greater the surface area the higher the reaction rate.
Surface area ONLY affect reactants that are in DIFFERENT phases. For example; Solid and a
liquid, liquid and a gas etc. It does not affect reactants that are in the same phase.
To summarize the 3 ways to change the rate of a reaction.
If you can make the reactants:
MOVE FASTER, HIT each other MORE OFTEN with MORE ENERGY
The reaction rate will INCREASE
4. Catalyst
A catalyst is a substance that can ALWAYS speed up the rate of a reaction but it is not used up
in the reaction. It does not change the products, it only helps make the products faster.
In your body, or in biology, a catalyst is called an enzyme. There are 1000’s of enzymes that
control everything in your body. Enzymes are large organic molecules.
Ex, Saliva, contains the enzyme amylase. Amylase helps digest carbohydrates in your mouth.
Catalysts have the ability to lower the energy it takes to break the bonds that start the
reaction. Therefore less energy is required to start the reaction so the reaction will go faster.
Ex; Catalytic converters on your exhaust in your car. Have a large surface area for a fast
reaction. They are coated with platinum, rhodium and palladium. The catalytic converter
removes the poisonous gases that are produced by your car.
2CO + O2 → 2CO2
2N2O3 → 2N2 + 3O2
hydrocarbons + O2 → CO2 + H2O
Enthalpy (H) & enthalpy change (H )
Enthalpy
- the “heat content” of a substance
or - the total KE & PE of a substance at const. pressure.
Chemists interested in enthalpy changes (H )
Exothermic reaction energy is released into the surroundings. The environment will get
warmer and the reaction will be colder.
If the reaction gets colder then it lost heat so the H is negative
H + H → H2 + heat
H+H
Enthalpy (H)
Heat is released to surroundings.
H is negative (-)
H
Exother
mic
H2
Reaction Proceeds
Endothermic reaction energy is absorbed from the surroundings. The environment will get
colder and the reaction will be warmer.
If the reaction gets warmer then it gained heat so the H is positive
O2 + Heat → O + O
O + O
H
Enthalpy (H)
O2
Heat is absorbed from the surroundings.
H is positive (+)
Endother
mic
Reaction Proceeds
Equations and heat
H = - 20 KJ
( -ive H means exothermic)
 shown H2 + S → H2S
6C + 3H2 → C6H6
H = + 83 KJ ( +ive H means endothermic)
beside
Thermochemical equations:
(“Heat Term” is in the equation. NO “H” shown beside the equation!)
- “heat term” shown on left side of arrow - endothermic (“it uses up heat like a reactant”)
eg.
CH3OH + 201KJ  C(s) + 2H2(g) + ½ O2(g)
-“heat term” shown on right side of arrow -exothermic ( “it gives off heat like a product”)
eg.
S(g) + O2(g)  SO2(g) + 296 kJ
pg 119 # 70 - 80
Chapter 6 - Chemical Reactions
Factors Affecting the Rate of Reactions
The rate of a reaction is the measure of how _______ the reactants can change into products.
If the reaction takes a long time then it has a LOW reaction rate. If the reaction goes quickly
it has a HIGH reaction rate.
There are 4 different ways in INCREASE the reaction rate.
1. Temperature
Increasing the temp cause the reactants to ______________. If the reactants move faster
they will hit each other more often and with a greater energy this will help them have a successful
reaction.
If the temperature is decreased, then the particles will ______________ and hit with less
often with less energy.
Higher temp = faster reaction rate
Lower temp = slow reaction rate
2. Concentration
Concentration refers to the amount of reactants that are present in a certain area.
If the concentration of reactants are increased then there are more reactants in the certain
area, therefore the reactants have a ____________________________each other and
having a reaction.
If the concentration of reactants are decreased then there are less reactants in a certain
area. This will decrease the chance of the reactants hitting each other and the reaction rate
will slow down.
Concentration ONLY affects reactants in a aqueous or gas phase. It does not help a liquid or
a solid.
3. Surface Area
Surface area is a measure of how much area is exposed. If the surface area is large, then there
is a ____________________________ another reactant so the reaction rate will be high.
The greater the surface area the higher the reaction rate.
Surface area ONLY affect reactants that are in DIFFERENT phases. For example; Solid and a
liquid, liquid and a gas etc. It does not affect reactants that are in the same phase.
To summarize the 3 ways to change the rate of a reaction.
If you can make the reactants:
MOVE FASTER, HIT each other MORE OFTEN with MORE ENERGY
The reaction rate will INCREASE
4. Catalyst
A catalyst is a substance that can ALWAYS _____________________ of a reaction but it is
not used up in the reaction. It does not change the products, it only helps make the products
faster.
In your body, or in biology, a catalyst is called an____________. There are 1000’s of
enzymes that control everything in your body. Enzymes are large organic molecules.
Ex, Saliva, contains the enzyme amylase. Amylase helps digest carbohydrates in your mouth.
Catalysts have the ability to _____________________ it takes to
_____________________ that start the reaction. Therefore less energy is required to start
the reaction so the reaction will go faster.
Ex; Catalytic converters on your exhaust in your car. Have a large surface area for a fast
reaction. They are coated with platinum, rhodium and palladium. The catalytic converter
removes the poisonous gases that are produced by your car.
2CO + O2 → 2CO2
2N2O3 → 2N2 + 3O2
hydrocarbons + O2 → CO2 + H2O
Enthalpy (H) & enthalpy change (H )
Enthalpy
- the “heat content” of a substance
or - the total KE & PE of a substance at const. pressure.
Chemists interested in enthalpy changes (H )
_____________ reaction ____________________ into the surroundings. The
environment will get warmer and the reaction will be colder.
If the reaction gets colder then it lost heat so the ________________
H + H → H2 + heat
H+H
Enthalpy (H)
Heat is released to surroundings.
H is negative (-)
H
Exother
mic
H2
Reaction Proceeds
______________reaction _____________________ from the surroundings. The
environment will get colder and the reaction will be warmer.
If the reaction gets warmer then it gained heat so the ________________
O2 + Heat → O + O
O + O
H
Enthalpy (H)
O2
Heat is absorbed from the surroundings.
H is positive (+)
Endother
mic
Reaction Proceeds
Equations and heat
H = - 20 KJ
( -ive H means ______thermic)
 shown H2 + S → H2S
6C + 3H2 → C6H6
H = + 83 KJ ( +ive H means ______thermic)
beside
_______________________ equations:
(“Heat Term” is in the equation. NO “H” shown beside the equation!)
- “heat term” shown on ________ of arrow - ______thermic (“it uses up heat like a reactant”)
eg.
CH3OH + 201KJ  C(s) + 2H2(g) + ½ O2(g)
-“heat term” shown on ________ of arrow - ______thermic ( “it gives off heat like a product”)
eg.
S(g) + O2(g)  SO2(g) + 296 kJ
pg 119 # 70 - 80