Rates of reaction Flashcards
What 4 things affect the rate of reaction?
Catalyst
Concentration/pressure
Surface area
Temperature
What is it called when a collision of molecules is strong enough to break the old bonds and make new ones?
Successful or effective collision
What is it called when a collision of molecules isn’t strong enough to break the existing bonds?
Unsuccessful it ineffective collision
What is activation energy?
The minimum energy that a pair of colliding molecules need in order to react.
Apart from the activation energy what is something 2 molecules need in order to react?
They need the correct orientation
Why does increasing surface area of a solid increase the rate?
The rate depends on the frequency of successful collisions.
More molecules are exposed for collisions so they collide more frequently.
Therefore, there are more successful collisions per second.
Why does increasing the concentration of a solution increase the rate?
The rate depends on the frequency of successful collisions.
More molecules in a given volume so there will be more collisions per second.
Therefore, there are more successful collisions per second.
Why does increasing the pressure of a gas increase the rate?
The rate depends on the frequency of successful collisions.
Molecules move closer, more molecules in a given volume so more collisions per second.
Therefore, there are more successful collisions per second.
Why does increasing the temperature increase the rate?
The rate depends on the frequency of successful collisions.
Molecules have more kinetic energy, collide more frequently and more have at least the activation energy and can react when they collide.
Therefore, there are more successful collisions per second.
Why does using a catalyst increase the rate?
The rate depends on the frequency of successful collisions.
Provides an alternative pathway of lower activation energy so more molecules have at least the activation energy.
Therefore, there are more successful collisions per second.
What is the collision theory?
In order for a reaction to occur, two particles must collide with the correct orientation and with at least the activation energy.
What are the benefits of using a catalyst?
Lower temp needed Costs are lower Less emissions Fewer fossil fuels used More sustainable
What is a homogeneous catalyst?
Catalyst in the same state as reactants
What is a heterogeneous catalyst?
Catalyst in a different state to the reactants
What type of system is needed for a dynamic equilibrium to be set up?
A closed system
What is a dynamic equilibrium?
Rate of the forwards reaction = rate of backwards reaction.
The concentrations of reactants/products don’t change when equilibrium is reached.
What is a closed system?
Temperature, pressure and concentration are unaffected by outside influences
How will changing the concentration affect the equilibrium?
More reactants/less products - shifts right
Less reactants/more products - shifts left
How will changing the pressure affect the equilibrium?
Increase pressure, move in direction with less moles of gas.
Decrease pressure, move in direction with more moles of gas.
How will changing the temperature affect the equilibrium?
Increase - shifts to the endothermic reaction to remove the heat
Decrease - shifts to the exothermic reaction to replace the heat.
What is Le Chatelier’s principle?
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise/oppose the effect of the change.
What does a catalyst do to the equilibrium?
Nothing, it doesn’t change the equilibrium, it just decreases the time it takes to reach equilibrium.
How do you work out the equilibrium constant?
Concentration of products (X together)
Concentration of reactants (X together)
What are the units for Kc if there is 1 more mole of reactants than products?
dm^3mol-1
