Unit 1: Section 5 - Kinetics, Equilibria and Redox Reactions Flashcards
What is the equation for reaction rate?
Reaction rate = Amount of reactant used or product formed / Time
What is collision theory?
A reaction between 2 particles won’t take place unless they collide in the correct orientation and with at least the minimum amount of kinetic energy required
What is the activation energy?
The minimum amount of kinetic energy that particles need to react
What does a Maxwell-Boltzmann distribution curve show?
The area under the graph - the total number of molecules
The curve starts at (0,0) - no molecules have zero energy
The peak - the most probable energy
To the right of the peak - mean energy of all the molecules
Molecules that can react - to the right of the activation energy
How does increasing the temperature affect the rate of reactions?
- If you increase the temperature of a reaction, the particles will on average have more kinetic energy and will move faster therefore the rate of reaction will be faster
- A greater number of particles will have at least the activation energy and be able to react
3 .This pushes the Maxwell-Boltzmann to the right, but there are the same number of particles so the area has to stay the same - as the molecules are moving faster, they will also collide faster
- As you get 2 effects happening, small increases in temperature will led to large increases in reaction rate
How does increasing the concentration affect the rate of reactions?
- The particles will on average be closer together
- If they’re closer, they will collide more often
- If collisions happen more frequently, they’ll have more chances to react
- Therefore the rate of reaction increases
How does increasing the pressure affect the rate of reactions?
- More of the gas particles are closer together
- So they are more likely to collide so collisions take place more frequently
- Therefore the reaction rate increases
What is a catalyst?
A substance that increases the rate of a reaction by providing an alternative pathway with a lower activation energy, the catalyst is chemically unchanged at the end of the reaction
How do catalysts work?
- Provide an alternative reaction route of lower activation energy
- More particles have energy > activation energy, so more frequent successful collisions, so increased reaction rate
How do catalysts affect graphs?
- In an energy profile, the activation energy will be lowered
- In a Maxwell-Boltzmann distribution curve, the activation energy line is shifted the the left
How to measure reaction rates by timing how long it takes for a precipitate to form?
- Used when the product is a precipitate which clouds the solution
- Watch a cross through the solution and time how long it takes to disappear
- You need to have the same observer every time, and the same cross because roughly the same amount of precipitate will be produced when the cross is obscured
- This is a very subjective method though
How to measure reaction rates by measuring a decreases in mass?
- Used when the product is a gas
- As gas is produced, the mass of the reaction mixture decreases
- The method is accurate, but as releases gas into the atmosphere, it is usually done in a fume cupboard
How to measure reaction rates by measuring the volume of gas given off?
- Use a gas syringe to measure the volume of gas being produced
- Gas syringe usually gives the volume to the nearest 0.1cm^3 so is usually an accurate method
What is dynamic equilibrium?
When the forward reaction is going at the same rate as the backward reaction so the concentrations of reactants and products stays constant
This can only happen in a closed system
What is Le Chatelier’s principle?
If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change