Kinetics Revision
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Kinetics Revision A-Level Chemistry
description
Revision of kinetics topic for A-level chemistry. Includes information about collision theory, rates of reaction and activation energy.
Transcript of Kinetics Revision
Kinetics Revision
A-Level Chemistry
Collision Theory
What is collision theory?
For molecules to react they must first collide
In addition, they must be the right orientation …
… and have enough energy
cv cv
What affects reaction rate?
TemperaturePressure
ConcentrationParticle size
Catalyst
How fast a chemical reaction goes is affected by many factors.
List them …
What about enzymes?
Enzymes are biological catalysts and for our purposes will be considered the same
as chemical catalysts
How fast a chemical reaction goes is affected by many factors.
List them ...
Chemical reaction rates
Temperature
Why does sugar dissolve in tea faster than water?
High Temp
Molecules have more energy …
… fewer collisions
Low Temp
Molecules have less energy …
… fewer collisions
As surface area increases the rate
of reaction generally increases
The particles on the
surface can react
When cut into smaller pieces the particles on the inside
can react
Chemical reaction rates
Surface Area
Which one will dissolve first in a cup of tea?
As the concentration of reactants increases, so does the likelihood that reactant molecules will
collide …The fewer red particles in a volume - the less chance of a collision
The more red particles in the same volume -
there is more chance of a collision
Chemical reaction rates
Concentration
… the rate of reaction increases
Chemical reaction rates
PressureWhat happens if you
increase the pressure in a reaction?
Increase in Pressure
Molecules are closer together
Number of collisions increases
Rate of reaction increases
A substance that increases the rate
of a reaction without being
consumed in the reaction
Chemical reaction rates
Catalysts
What is a catalyst?Provide an alternative pathway for reactions
… are biological catalysts (proteins) that increase the rate of biochemical reactions
Enzymes …
Chemical reaction rates
Look at the picture below …A =B =
reactants
products
Activation energy
The energy required for two
colliding molecules to
react
Activation Energy
Our picture from before can be redrawn …
Enthalpy
Extent of reaction
Activation energy (Ea)
enthalpy = energy
Activation Energy
Enthalpy
Extent of reaction
Ea
Energy of reactants
Energy of products
Because …
Energy of reactants
Energy of products
Exothermic
>
Energy given out
Activation Energy
Enthalpy
Extent of reaction
Energy of reactants
Energy of productsEa
Because …
Energy of reactants Energy of products
Endothermic
>Energy
taken in
