Rates of reaction Flashcards
(26 cards)
What are the variables that affect rates of reaction?
Temperature
Concentration
Surface area
Pressure
What has to happen for a reaction to take place?
Collisions with activation energy
What is the activation energy?
The lowest amount of energy that collision particles must have to react together
What will happen if you increase one of the variables?
The rate of reaction will increase as the frequency of collisions will increase
What happens if the concentration is high?
There is more particles per unit volume so there is more frequent collisions so it is faster
What happens if the concentration is low?
There is fewer particles so there is less collisions so it is slower
If the particles are smaller is the surface area bigger?
Yes as the SA:Vol is bigger
What happens if the surface area is bigger?
There is more frequent collisions so it is faster
What happens if the pressure is high?
The particles are closer together so there is more collisions so it is faster
What happens if the pressure is low?
The particles are further apart so there is less collisions so the rate is slower
What happens if the temperature is higher?
The particles have more energy so they move faster, colliding so more of these collisions have the activation energy so it is faster
What happens if the temperature is lower?
The particles have less energy so they move slower, colliding less so less of these collisions have the activation energy so it is slower
What is a catalyst?
A substance that speeds up the rate of reaction by lowering the activation energy of the reaction
How do catalysts lower the activation energy?
By providing an alternative reaction pathway
Are catalysts ever used up?
no so they can be reused
In reversible reactions if one way is exothermic, what will the other way be?
Endothermic
What is Le Chatelier’s Principle?
The idea if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change
What can Le Chatelier’s Principle be used to do?
To predict the effect of any changes you make to a reaction system
What will happen to equilibrium if you decrease the temperature?
It will move in the exothermic direction to produce more heat so there will be more products in the exothermic side and fewer in the endothermic
What will happen to equilibrium if you increase the temperature?
It will move in an endothermic direction to decrease the temperature so there will be more products on the endothermic side and fewer on the exothermic
What will happen to equilibrium if you increase the pressure?
Equilibrium tries to reduce it so moves in the direction of fewer molecules of gas
When does changing the pressure only ever affect?
When an equilibrium involves a gas
What will happen to equilibrium if you decrease the pressure?
Equilibrium tries to increase so moves in the direction of more molecules of gas
What happens when you change the concentration of either the reactants?
The system will no longer be at equilibrium
