1.5 Kinetics
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Collision theory
For a reaction to occur, particles must collide with sufficient energy and be in the correct orientation
Activation energy
The minimum energy required to start a reaction by the breaking of bonds
Rate of reaction
The change in concentration of a substance in a given time
As a reaction proceeds, the rate _________ as…..
decreases ….the concentration of reactant falls
Increasing concentration ________ the rate of reaction
Increases - Number of particles per unit volume increases - So the number of successful collisions per unit time increases
Increasing pressure ________ the rate of reaction
Increases - Number of particles per unit volume increases - So the number of successful collisions per unit time increases
Increasing surface area ________ the rate of reaction
Increases - More particles are exposed to the other reactant - So the number of successful collisions per unit time increases
Increasing temperature ________ the rate of reaction
Increases - More molecules have E>Ea - So the number of successful collisions per unit time increases
Adding a catalyst ________ the rate of reaction
Increases An alternative reaction pathway with a lower Ea is provided
What is a Maxwell-Boltzmann distribution
A graph of number of molecules against their energy
Features of a Maxwell-Boltzmann distribution
• Area under curve = total number of molecules • Graph starts at the origin • Highest point = most probable energy and is to the left of the average (graph skewed to the right) • No maximum energy (graph doesn’t reach x-axis)
Why does the Maxwell-Boltzmann distribution graph start at the origin but not reach the x-axis on the right
There are no particles with zero energy, but there is no maximum energy of particles
Effect on the Maxwell-Boltzmann distribution when temperature is increased
Peak shift to the right and downwards, area remains the same