Kinetics Flashcards
What is the rate of reaction?
The reaction rate is defined as the change in concentration (or amount) of a reactant or product over time.
How do particle react?
Particles must collide to react.
A reaction won’t take place between to particles unless:
-They collide in the right direction (they need to be facing each other in the right way)
- They collide with at least a certain minimum amount of kinetic energy
What is the activation energy?
The minimum amount of kinetic energy that particles need to react is called the activation energy.
What does the area underneath a Maxwell-Boltzmann distribution curve show?
The area underneath the curve is equal to the total number of molecules
What does the peak of the M-B distribution curve show?
The peak of the curve represents the most likely energy of any single molecule.
Where is the mean energy located on the M-B curve?
This energy is located a bit to the right of the peak.
Which molecules can react on the M-B distribution curve?
The number of molecules which can react are the ones with more than the activation energy.
How does increasing the temperature affect the M-B distribution curve?
Increasing the temperature means that he particles have more kinetic energy and therefore move faster.
A greater proportion of molecules will have at least the Activation Energy and be able to react.
As well as this, the molecules will begin to collide more frequently.
This causes the M-B curve to be shifted over to the right.
How does increasing the concentration affect the rate of reaction?
If you increase the concentration of a solution, the particles will be closer together.
If they’re closer they’ll collide more frequently and therefore there will be a higher chance of reaction.
How does increasing the pressure affect the rate of reaction?
If a reaction is involving gases, increasing the pressure will act in the same way as increasing the concentration.
Raising the pressure pushes all of the gas particles closer together, making them more likely to collide= collisions happen more frequently and the reaction rate increases.
What is a catalyst?
A catalyst is a substance that increases the rate of reaction by providing an alternative reaction pathway with a lower Ea.
the catalyst is chemically unchanged at the end of the reaction.
How does adding a catalyst affect the rate of reaction?
Because the catalyst lowers the Ea, there are more particles with enough energy to react when they collide.
So, in a certain amount of time, more particles react.
How can you measure reaction rates?
- Timing how long a precipitate takes to form
- measuring a decrease in mass
- Measuring the volume of gas given off.
Describe the method for timing how long it takes for a precipitate to form.
- You can use this method when the product is a precipitate which clouds a solution
- You watch a mark through the solution and time how long it takes to be obscured
- If the same observer uses the same mark each time, you can compare the rates of reaction because (roughly) the same amount of precipitate will have been formed when the mark becomes obscured.
- But this method is subjective- different people may not agree on the exact moment the mark disappears.
Describe a method for measuring a decrease in mass.
- When one or more of the products is a gas, you can measure the rate of formation using a mass balance.
- As a gas is given off, the mass of the reaction decreases.
- This method is accurate and easy to do. Bu it does release gas into the atmosphere, so it’s usually done in a fume cupboard.
