3.1.5 Kinetics Flashcards
What is rate of reaction?
Rate of reaction is the change in the amount of reactant or product over time
What does collision theory state
Reaction won’t take place between two particles unless the conditions are correct
What are the conditions in collision theory which allow reactions to take place (direction)?
Particles need to collide in the right direction (facing each other the right way)
What are the conditions in collision theory which allow reactions to take place (energy)?
Particles need to collide with at least a certain minimum amount of kinetic energy (activation energy)
Define activation energy
minimum amount of kinetic energy particles need to react
What is activation energy needed for?
this much energy is needed to break the bonds within reactant particles to start the reaction
How easily do reactions with low activation energies happen
Reactions with low activation energies often happen easily
How easily do reactions with high activation energies happen
Reactions with high activation energies don’t happen easily
Why does a Maxwell Boltzmann graph start at (0,0)
Because no molecules have zero energy
What does the peak of the curve on a Maxwell Boltzmann graph represent
Peak of the curve represents the most probable energy (Emp) of any single molecule
What does just right of the peak of a Maxwell Boltzmann graph show?
Mean average energy of all the molecules is a bit to the right of the peak
What does the area under a Maxwell Boltzmann distribution curve show
Area under a Maxwell Boltzmann distribution curve is equal to the total number of of molecules
How does temperature affect rate of reaction?
Increasing the temperature, increases rate of reaction
What happens to the proportion of molecules with at least the activation energy when temperature is increased
Greater proportion of molecules will have at least the activation energy and be able to react
What happens when you increase temperature in terms of energy
If you increase temperature, the molecules will on average have more kinetic energy and will move faster
What happens to molecules due to their increase in kinetic energy after a temperature increase
The molecules will be moving around quicker so they will collide more often
How will increasing temperature affect the shape of the Maxwell Boltzmann distribution curve?
Increasing temperature will push the Maxwell Boltzmann distribution curve over to the right
How will decreasing temperature affect the shape of the Maxwell Boltzmann distribution curve?
Decreasing temperature will the push the Maxwell Boltzmann distribution curve over to the left
Does changing temperature change the area under the Maxwell Boltzmann distribution curve?
No as number of molecules stays the same
Does changing temperature change the activation energy
Changing temperature doesn’t change the activation energy
How does increasing temperature affect the most probable energy
Increasing temperature increases the most probable energy
How does decreasing temperature affect the most probable energy
Decreasing temperature will decrease the most probable energy
How does concentration affect rate of reaction
Increasing concentration will increase rate of reaction
What does increasing concentration do to how close particles are together
If you increase the concentration of reactants in a solution, the particles will on average be closer together
What happens as a result of particles being closer together
If particles are closer together, collisions are more frequent
What happens if collisions are more frequent
If collisions are more frequent, there will be more chances for particles to react so rate of reaction increases
How does changing concentration affect activation energy value
Changing concentration doesn’t change activation energy value
How does changing concentration affect most probable energy value
Changing concentration doesn’t change most probable energy value
How does increasing concentration affect area under the Maxwell Boltzmann distribution curve?
Increasing concentration increase area under Maxwell Boltzmann distribution curve
If concentration is doubled, so will the area
How does decreasing concentration affect area under Maxwell Boltzmann distribution curve
Decreasing concentration decreases area under Maxwell Boltzmann distribution curve
If concentration is halved, so will the area
How does increasing concentration affect the number of molecules with energies above activation energy
Increasing concentration increases molecules available to collide in a given volume. Will also be more molecules with energies above the activation energy
How does increasing temperature affect the number of molecules that have at least the activation energy
At higher temperatures, more molecules have at least the activation energy
How does changes in pressure affect rate of reaction
Changes in pressure affect rate of reaction the same way as changes in concentration
What can you use catalysts to do?
You can use catalysts to make chemical reactions happen faster
What does a catalyst do to rate of reaction
A catalyst increases the rate of a reaction
How does a catalyst increase rate of reaction
Catalyst increases rate of reaction by providing an alternative reaction pathway with a lower activation energy
Do catalysts get used up in reactions
Catalysts don’t get used up in the reaction
Do catalysts take part in reactions
Catalysts do take part in reactions but are remade at the end of them
Why does lowering activation energy increase rate if reaction
More particles with enough energy to react when they collide so in a set time more particles react
Does adding a catalyst change the shape of the Maxwell Boltzmann distribution curve?
Maxwell Boltzmann distribution curve is unchanged as molecules still have the same amount of energy
Does adding a catalyst change the activation energy
Adding a catalyst lowers the activation energy, so shifts it to the left on a Maxwell Boltzmann distribution curve
How do you work out rate of reaction?
(Amount of reactant used or product formed) / (time)
How does increasing pressure increase rate of reaction
Increasing pressure pushes all of the particles closer together so increases the number in a given volume, this increases the frequency of collisions and so also rate of reaction
measuring rate of reaction practical:
step 1
draw a black cross on a white tile and place a conical flask on top
measuring rate of reaction practical:
step 2
add the fixed volumes of sodium thiosulfate solution and HCl into the conical flask, measure initial temp and start stopwatch
measuring rate of reaction practical:
step 3
wait until cross disappears (precipitate forms) and stop the stopwatch, noting down the time. Record temp of solution
measuring rate of reaction practical:
step 4
calculate average temperature using the initial and final temperatures
measuring rate of reaction practical:
step 5
repeat practical at different temperatures, as temp increases so should rate of reaction
how does surface area affect rate of reaction
increasing surface area increases rate of reaction
how does increasing surface area increase rate of reaction
more particles are exposed to the other reactant
there is a greater chance of particles colliding, which leads to more successful collisions per second
the rate of reaction increases
