Reaction rates Flashcards
What is the rate of a reaction?
The change in concentration of a reactant of product in a given time
What is the equation for the rate of a reaction?
rate = change in concentration / time
What is the units for the rate of a reaction?
mol dm^-3 s^-1
When is the rate of reaction fastest?
At the start of the reaction, as each reactant is at its highest concentration
When does the rate of reaction become zero?
Once of the reactants has been completely used up, the concentrations stop changing and the rate of the reaction is 0
What 4 factors can change the rate of a chemical reaction?
- Concentration (or pressure when reactants are gases)
- Temperature
- Use of catalyst
- Surface area of solid reactants
What does the collision theory state?
2 reacting particles must collide for a reaction to occur
What is an effective collision?
One that leads to a chemical reaction
What are the 2 conditions for a reaction to be effective?
- The particles collide with the correct orientation
- The particles have sufficient energy to overcome the activation energy barrier of the reaction
How does increasing the concentration affect the rate of reaction?
- When the concentration of a reactant is increased, the rate of reaction generally increases
- An increase in concentration increases the number of particles in the same volume
- The particles are closer together and collide more frequently
- In a given period there will be more effective collisions and therefore an increased rate of reaction
How does increasing the pressure of a gas affect the rate of reaction?
- When a gas is compressed into a smaller volume the pressure of a gas in increased and the rate of reaction increases
- The concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume
- The gas molecules are closer together and collide more frequently, leading to more effective collisions
If a reaction produces a gas, what 2 methods can be used to determine the rate of reaction?
- Monitoring the volume of gas produced at regular time intervals using gas collection
- Monitoring the loss of mass of reactants using a balance
The volume of gas produced and mass loss are both proportional to the change in concentration of a reactant or a product; so the change in volume or mass with time both give a measure of the rate of reaction
If a reaction produces a gas, what 2 methods can be used to determine the rate of reaction?
- Monitoring the volume of gas produced at regular time intervals using gas collection
- Monitoring the loss of mass of reactants using a balance
The volume of gas produced and mass loss are both proportional to the change in concentration of a reactant or a product; so the change in volume or mass with time both give a measure of the rate of reaction
What is a catalyst?
A substance that changes the rate of a chemical reaction without undergoing any permanent change itself
What are the rules of a catalyst?
- The catalyst is not used up in the chemical reaction
- The catalyst may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
- At the end of the reaction the catalyst is regenerated