Unit 6 - Rate And Extent Of Chemical Change Flashcards
How to work out mean rate of reaction
Quantity of product or reactant formed / time taken
What is collision theory
Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy. The rate of a chemical reaction is determined by the frequency of successful collisions
What does frequency mean in collision theory
Means the number of successful collisions per second
What happens when a solid reacts with a solution in terms of particles
The particles in the solution can only react with particles on the surface of the solid
How does surface area affect rate of reaction
More particles available to react so more frequenct collisions
We have more collision per second so rate will increase when surface area is increased
How does surface area to volume ration affect rate of reaction
Smaller sized blocks of solid reactant have a great surface area to volume ratio than large blocks, this means more particles on the surface so there are more collisions per second so increased rate of reaction
What happens if two particles with small amounts of energy collide
Because they have low energy they cannot overcome the activation energy barrier, so they would not collide successfully and no reaction would occur
What happens if two particles both with large amounts of energy collide
They have enough energy to overcome the activation barrier and collide successfully, a reaction would take place
How does temperature affect rate of chemical reactions
-increases the rate of reactions
-as increase temperature will increase kinetic energy in particles
-as they have more energy they can move faster
-this increases frequency of collisions, there is a greater number of collisions per second
-each collision has more energy so more particles can overcome activation barrier and collide successfully
What is a catalyst
Increase the rate of chemical reactions but are not used up during the reaction
Advantages of catalysts
Allow us to carry out reactions quickly without needing to increase temperature so they save money, as they are not used up during a reaction we can reuse them
How do catalysts affect rate of reaction
Increase the rate by providing a different pathway for the reaction that has a lower activation energy so less energy required to cross activation energy barrier so more particles successfully collide per second
Why don’t we include catalysts in the chemical equation for a reaction
They are not used up in the reaction
How do we know if a reversible reaction is Exothermic or endothermic
If a reversible reaction is Exothermic in one direction it is endothermic in the opposite direction ,the same amount of energy is transferred in each case
What is equilibrium
The forward and the reverse reactions will take place at the exact same rate this point is equilibrium
What are the effects of changing conditions on equilibrium
If a system is at equilibrium and a change is made to the conditions then the system responds to counteract the change, this is called la chateliers principle
Factors that affect rate of chemical reaction
the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts
How does concentration affect rate of a reaction
If it is more concentrated then there are more particles in the same volume, this makes more collisions between reactant particles and are more frequent
How does pressure affect rate of reaction
when pressure is increased it means that the same number of particles occupy a smaller space this makes more collisions between reactant particles and are more frequent
How to work out rate of a reaction
Amount of reactant used or amount of product formed / time
What is the scientific term for saying that the cloudiness of a solution changes
The turbidity changes
Give an example of a slow reaction
Rusting of iron
Examples of a fast reaction
Explosions
What is a reversible reaction
the products of the reaction can react to produce the original reactants
Rules for reversible reactions
If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.
The same amount of energy is transferred in each case
What is equilibrium
When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate.
What is effect of changing conditions on equilibrium
If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.
The effects of changing conditions on a system at equilibrium can be predicted using Le Chatelier’s Principle
How does changing concentration affect equilibrium
If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.
How does temperature affect equilibrium
If the temperature of a system at equilibrium is increased:
-the relative amount of products at equilibrium increases for an endothermic reaction
-the relative amount of products at equilibrium decreases for an exothermic reaction.
If the temperature of a system at equilibrium is decreased:
-the relative amount of products at equilibrium decreases for an endothermic reaction
-the relative amount of products at equilibrium increases for an exothermic reaction.
How does pressure affect equilibrium
For gaseous reactions at equilibrium:
-an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of gas molecules as shown by the symbol equation for that reaction
-a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction
Why does changing temperature always affect equilibrium
-Increasing the temperature shifts the equilibrium in the direction of the endothermic
-Decreasing the temperature shifts the equilibrium in the direction of the exothermic
