C2.4 Rates of reaction Flashcards
When can chemical reactions occur?
when reacting particles collide with each other and with sufficient energy
What is the activation energy?
the minimum amount of energy particles must have to react
What 5 ways can you increase the rate of reaction?
- increase temperature
- increase pressure of reacting gases
- increase concentration of reactants in solutions
- increase surface area of solid reactants
- use a catalyst
How does increasing the temperature increase the rate of reaction?
increases speed of reacting particles- move faster
so that they collide more frequently and more energetically
more of the collisions are successful (more of the particles have the activation energy)
How does increasing the pressure of reacting gases increase the rate of reaction?
particles are closer together
increases the frequency of collisions
How does increasing the concentration of the reactants in solutions increase the rate of reaction?
Rate of reaction increases as there are more particles per unit volume
so there is an increase in the frequency of collisions
How does increasing the surface area of solid reactants increase the rate of reaction?
increases the frequency of collisions
Describe catalysts
- change the rate of chemical reactions (speed up)
- are not used up during a chemical reaction
- different reactions need different catalyst
What is an advantage of using catalysts?
-used in industrial processes to reduce costs- allow reaction to work at lower temperature- less energy needed.
What are some disadvantages of using catalysts?
- expensive to buy
- often need to be removed and cleaned
- catalysts can be ‘poisoned’ by impurities so stop working
Describe 3 ways to measure the rate of reaction
1) precipitation- see how long it takes for a solution to turn from cloudy to clear
2) change in mass (gas given off)- use scales to measure mass before and after reaction
3) volume of gas give off- use a gas syringe. the more gas given off in a given time then the faster the rate of reaction.
What are the 2 ways you can find the rate of reaction?
- amount of reactant used (divided by) time
- amount of product formed (divided by) time
Why does a catalyst work for a longtime before it needs replacing?
Because it is not used up in the reaction
Although gold is expensive and rare, suggest why it is still used as a catalyst in industrial processes
gold is the only catalyst for some reactions
catalysts are nit used up
improves the speed of the reaction
only small quantities are needed
