Topic 6 - The Rate And Extent of chemical change Flashcards
How can you find the rate of a chemical reaction?
By measuring the quantity of a reactant used or the quantity of product formed over time
What factors affect the rates of chemical reactions?
- Concentrations of reactants in solution
- Pressure of reacting gases
- Service area of solid reactants
- Temperature
- Presence of catalysts
How does increasing the temperature increase the rate of reactions?
The particles move faster and collide more frequently so there is more energy
How does increasing the concentration increase the rate of reactions?
If the solution is more concentrated there are more particles in the same volume so collisions are more frequent
How does increasing pressure increase the rate of reactions?
The same number particles occupy a smaller space so collisions happen more frequently
How does increasing the surface area increase the rate of reactions?
For the same volume of the solid the particles around it will have more area to work on so there will be more collisions
How does using a catalyst increase the rate of reactions?
A catalyst is a substance that speeds up a reaction without being used up in the reaction its self
How do you catalysts work?
They decrease the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy
What does collision theory explain?
How various factors affect rates of reactions
What is the collision theory?
Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy
What is activation energy?
The minimum amount of energy that particles must have to react
What increases the frequency of collisions?
- The concentration of reactants in solution
- The pressure of reacting gases
- The surface area of solid reactants
How do you increase the energy of collisions?
Increase the temperature
Do all reactions need the same catalysts?
No, different reactions need different catalysts
Give an example of a biological catalyst?
Enzymes
What are reversible reactions?
In some chemical reactions the products of the reaction can react to produce the original reactants
How can you change direction of reversible reactions?
By changing the conditions for example heating and cooling
If a reversible reaction is exothermic in One Direction what happens in the opposite direction?
It is endothermic but the same amount of energy is transferred in each case
What is equilibrium?
When the forward and reverse reactions occur at exactly the same rate
When does equilibrium occur?
When a reversible reaction occurs in apparatus which prevent the escape of reactants and products
What do the relative amounts of all the reactants and products at equilibrium depend on?
The conditions of the reaction
What happens if a system is at equilibrium and a change is made to any of the conditions?
The system responds to counteract the change
How can we predict the effects of changing conditions on the system at equilibrium?
Using Le Chatelier’s principle
What is Le chatelier’s principle?
The idea that if you change the conditions of a reversible reaction at equilibrium the system will try to counteract that change
What happens if the concentration of one of the reactants or products is changed during equilibrium?
The system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again
What happens if the concentration of reactants is increased?
More products will be formed until equilibrium is reached again
What happens if the concentration of a product is decreased?
More reactants will react until equilibrium is reached again
What happens if the temperature of a system at equilibrium is increased for an endothermic reaction?
The relative amount of products at equilibrium increases
What happens if the temperature of the system at equilibrium is increased for an exothermic reaction?
The relative amount of products at equilibrium decreases
What happens if the temperature of the system at equilibrium is decreased for an endothermic reaction?
The relative amount of products at equilibrium decreases
What happens if the temperature of the system at equilibrium is decreased for an exothermic reaction?
The relative amount of products at equilibrium increases
What does an increase in pressure for gaseous reactions at equilibrium cause?
The equilibrium position will shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction
What does a decrease in pressure for gaseous reactions at equilibrium cause?
Equilibrium position will shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction
