6 Chemical Kinetics
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When was kinetic theory developed and why?
The kinetic theory developed in the 18th century out of a need to explain how it is that gases exert pressure inside a container
What type of states of matter does kinetic theory account for?
The kinetic theory of matter accounts for the properties of solids, liquids, and gases in terms of the interactions of particles and their relative energies
What is the average kinetic energy of the particles directly proportional to?
The average kinetic energy of the particles is directly proportional to the temperature of the system in Kelvin
What is kinetic energy?
Kinetic energy refers to the energy associated with movement or motion. It is determined by the mass and velocity of the substance
What is the equation for kinetic energy?
KE = ½mv2
What is there an inverse relationship between due to the kinetic energy of the particles being equal at the same temperature?
As the kinetic energy of the particles at the same temperature is equal, this means there is an inverse relationship between mass and velocity
What does this inverse relationship explain?
This is why substances with a lower mass diffuse more quickly than those with greater mass at the same temperature
What 4 factors determine the rate of a chemical reaction?
collision frequency collision energy activation energy collision geometry
What is the collision frequency?
If a chemical reaction is to take place between two particles, they must first collide The number of collisions between particles per unit time in a system is known as the collision frequency
how can collision frequency be changed?
The collision frequency of a given system can be altered by changing the concentration of the reactants, by changing the total pressure, by changing the temperature or by changing the size of the reacting particles
What is it called when the collision of two molecules does not result in a reaction?
Not all collisions result in a chemical reaction Most collisions just result in the colliding particles bouncing off each other Collisions which do not result in a reaction are known as unsuccessful collisions
When do unsuccessful collisions occur?
Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds If they do not have sufficient energy, the collision will not result in a chemical reaction
When will a reaction be successful in terms of collision energy? What is collision energy?
If they have sufficient energy, they will react, and the collision will be successful The combined energy of the colliding particles is known as the collision energy
What is the activation energy?
The minimum energy the colliding particles need in order to react is known as the activation energy
When will a reaction be unsuccessful, in terms of activation energy?
If the collision energy of the colliding particles is less than the activation energy, the collision will be unsuccessful
When will a reaction be successful, in terms of activation energy?
If the collision energy is equal to or greater than the activation energy, the collision will be successful, and a reaction will take place
How can the activation energy of a reaction be changed?
The activation energy can be changed by the addition of a catalyst
What does collision geometry mean in terms of a successful reaction? When is collision geometry particularly important?
Particles have to have the right orientation when they collide for the reaction to be successful This is particularly the case with large molecules with complex shapes
Why do most collisions not result in a reaction?
Most collisions do not result in reaction because they do not reach the activation energy rather than not having the correct collision geometry
How do the concentrations of reactants and products change as a reaction progresses?
As a chemical reaction proceeds, the concentration of the reactants decreases and the concentration of the products increases
What is the rate of reaction?
The rate of a reaction is the speed at which a chemical reaction takes place and has units mol dm-3 s-1
How can the rate of reaction be calculated?
rate of reaction = change in amount of reactants or products mol dm-3 s-1 / time (s) (basically the gradient of the graph)
What is the basis of measuring the rate of reaction?
To measure the rate of a reaction, we need to be able to measure either how quickly the reactants are used up or how quickly the products are formed
What does the method used to measure rate depend on? very very basic
The method used for measuring depends on the substances involved