Booklet 6 - Rates Of Reaction Flashcards
What is the rate of a chemical?
Tells you how fast reactants turn into products
What two ways can we measure the rate of a chemical reaction?
1) . Measuring how quickly the reactants are used up
2) . Measure how quickly a product is made
Whats the equation for the mean rate of a reaction (reactant)?
Quantity of reactant used ➗ time taken
Whats the equation for the mean rate of a reaction (product)?
Quantity of product formed ➗ time taken
What two descriptions can be made from seeing the rate of a reaction on a graph?
1) . The steeper the line the faster the rate
2) . As reactants are used up the concentration of these reactant particles decreases, there are few available then, so the rate decreases and eventually the gradient becomes zero ie a horizontal line
What is the collision theory?
Explains how various factors affect rates of reaction
What does the collision theory suggest?
That chemical reactions only occur when reacting particles collide with each other and with sufficient energy
What is the minimum amount of energy particles require called?
The minimum amount of energy that particles must have to react is called the activation energy
How does temperature affect rate?
Increasing the temperature increases the speed of the reacting particles so that they collide more & more energetically. The activation energy is overcome more often and the rate increases
How does concentration affect rate?
Increasing concentration of reactants in solutions or increasing the pressure of reacting gases also increase the frequency of collisions as they’re now closer together, and so increase the rate
How does surface area affect rate?
Large pieces of solid have a small area relative to their volume ie their inner surfaces aren’t exposed & are not available to react. Therefore, fewer collisions occur and the reaction is slower
How can you increase the SA to increase the rate?
Breaking the solid into smaller pieces increases the S.A to volume ratio, so for the same volume of the solid, the particles around it will have more area to work on, increasing the frequency of collisions and therefore increasing rate.
What are catalysts?
Catalysts change the rate of reaction but are not used up during the reaction.
- Different catalysts are required for different reactions
How do catalysts affect rate?
They increase the rate of reaction by providing a different pathway for the reaction, that has a lower activation energy
What’s a reversible reaction?
In some chemical reactions, the products of the reaction can react to produce the original reactants
How is a reversible reaction represented?
A + B -> C + D
What two things could a reversible reaction show?
If a reversible reaction is exothermic in one direction, and endothermic in the opposite direction. The same amount of energy is transferred in each case
When is equilibrium reached?
When a reversible reaction occurs in a apparatus or closed system, nothing can escape or be added, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate
What do the relative amounts of all the reactants and products at equilibrium depend on?
The conditions of the reaction
What happens when a change is made to a system that has reached equilibrium?
If a change is made to any of the conditions, then the system responds to counteract the change
What idea can we use to predict the effects of changing conditions on system at equilibrium?
Le Chatelie’s Principle
What is the effect of changing concentration?
If the concentration of one of the reactants or products is changed, 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 reactant is increased?
More products will be formed until equilibrium is reached again
What happens if the concentration of reactant is decreased?
More reactants will react until equilibrium is reached again
If the temperature of a system at equilibrium is increased what two things happen?
1) . The relative amount of products at equilibrium increases for an endothermic reactions
2) . The relative amount of products at equilibrium decreases for an exothermic reactions
If the temperature of a system at equilibrium is decreased what two things could happen?
1) . The relative amount of products at equilibrium decreased for an endothermic reactions
2) . The relative amount of products at equilibrium increases for an exothermic reactions
What does an increase in pressure do to the equilibrium?
Causes the equilibrium position to 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 do to the equilibrium?
Causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction
