topic 6 Flashcards
What does the rate of a chemical reaction depend on (2)
- the collision frequency of reacting particles. The more collisions there are the faster the reaction is
- the energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful
The more collisions there are ….
The faster the reaction is
What is the activation energy
The minimum amount of energy that particles need to react
Why do particles need activation energy
To break the bonds in the reactants and start the reaction
What is the rate of a reaction
How fast the reactants are changed into products
2 examples of slow reactions
- rustling of iron
- chemical weathering- acid rain damaging limestone buildings
An example of moderate speed reaction
-metal magnesium reacting with an acid to produce a gentle stream of bubbles
How can you find the speed of a reaction
By recording the amount of product formed r the amount of reactant used up over time
What does the rate of reaction depend on (4)
- temperature
- concentration of a solution or the pressure of gas
- surface area
- presence of a catalyst
What does more collisions increase
It increases the rate of reaction
3 ways in how increasing the temperature increases the rate
- when the temperature is increases, the particles all move faster
- if they are moving faster, they are going to collide more frequently
- the faster they move the more energy they have, so more of the collisions have enough energy to make the reaction happen
What does it mean if a solution is more concentrated
It means there are more particles knocking about in the same volume of water or other solvent
What happens when the pressure of gas is increased
It means the same number of particles occupies a smaller space- this makes collisions between the reactant particles more frequent
How can you increase the surface area of a volume
If one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio
How does increasing surface area increase rate
It means that for the same volume of the solid, the particles around it will have more area to work on so there will be collisions more frequently
What is a catalyst
A substance that speed up the rate of a reaction without being used up in a reaction itself
What do catalysts do in a rate of reaction
They work by decreasing the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy
What are enzymes
Biological catalysts- hey catalyse reactions in living things
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 can “Le Chatelier’s Principle” be used to predict
The effect of any changes you make to a reaction system
What does it mean if the equilibrium lies to the right
The concentration of products is greater than that of the reactants
What does it mean if the equilibrium lies to the left
The concentration of reactants is greater than that of the products
What does the position of equilibrium depend on what conditions (3)
- the temperature
- pressure
- concentration of the reactants and products
if you decrease the temp of a system, what happens to the equilibrium
it moves in the exothermic direction to produce more heat- this means you get more products for the exothermic reaction and fewer products for the endothermic reaction
what does changing the pressure have an affect on equilibrium involving …
gases only
what happens to the equilibrium if you increase the pressure
the equilibrium tries to reduce it- it moves in the direction where there are fewer molecules of gas
what happens to the equilibrium if you decrease the pressure
the equilibrium tries to increase it- it moves in the direction of where there are more molecules of gas
when will a system no longer be at equilibrium
if you change the concentration of either the reactants or the products
what happens to the system if you increase the concentration of the reactants
the system tries to decrease it by making more products
what happens to the system if you decrease the concentration of products
the system tries to increase it again by reducing the amount of reactants
what does it mean if a system is at equilibrium
both reactions are still happening, but there is no overall effect. This means that the concentration of reactants and products have reached a balance and won’t change
how is equilibrium reached
equilibrium is only reached if the reversible reaction takes place in a ‘closed system’.
what is a closed system
it means that none of the reactants or products can escape and nothing else can go in
