Unit 3: Controlling The Rate Flashcards
Reaction rate
Must be controlled to make sure it is economically viable (result in good yield of product and profits) and safe (reaction does not progress too quickly, causing explosions)
Collision theory
For a chemical reaction to occur, reactant molecules must collide with enough energy to reach the minimum kinetic energy, called the activation energy (Ea)
Reactant molecules collide
As they collide they must have enough energy to overcome repulsive forces (caused by outer electrons) and start to break the bonds between atoms
Activated complex
An intermediate stage is reached and a high energy, unstable arrangement of atoms is formed called the activated complex
Product molecule forms
Energy is given out as new bonds are formed and the atoms are rearranged into the product molecule
Collision geometry
Must be right do that the activated complex can be formed, creating a successful collision.
Altering factors
Temperature
Concentration
Pressure
Particle size
Use of a catalyst
Temperature
If the temperature is increased the particles will have more energy, making them move quicker - increasing the rate of reaction because the particles will collide more often
Particle size
Decreasing the particle of a reactant, increases its surface area that collisions can take place on.
Pressure
If the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions.
Catalyst
Provide an alternative pathway for a reaction which is lower in energy, making them held at a favourable angle for collisions to occur.
Exothermic reaction
Energy of products - energy of reactants
Exothermic will always be
Endothermic reactions
Energy of products-energy of reactants
Endothermic always positive
Activation energy
Forward reaction= Ea - R
Reverse reaction= Ea - P
Enthalpy change
Forward = product - reactants (negative)
Reverse = reactants - products (positive)
