chapter 5 - kinetics Flashcards
Define kinetics
The change in concentration of a reactant (or product) over per unit time (S-1)
how can the rate of reaction be calculated from a graph
The rate of reaction can be calculated by drawing a tangent to the curve and calculating the gradient.
Factors affecting the rate of reaction
Catalyst-mainly in biology the pH can change and it can only affect the acids.
Collision theory-for particles to react they must collide with the activation energy or greater and the correct orientation.
activation energy-the minimum energy needed for a reaction to occur when two particles collide.
How does increasing the temperature affect the rate of reaction
Increasing the temperature will increase the energy of the particles, this will lead to more frequent collisions and more particles will have the activation energy or greater. This leads to more successful collisions per second.
how does decreasing the pressure Affect the rate of reaction, (only in gasses)
Decreasing the pressure only in gases will cause the particles to be further apart as the volume has increased, this will lead to less frequent collisions and less successful collisions per second. The energy of the particles does not change.
How does increasing concentration affect the rate of reaction
increasing concentration means more particles are in a fixed/given volume, therefore there are more frequent collisions and more successful collisions per second. However the energy of the particles does not change.
how does increasing the surface area affect the rate of reaction
Increasing the surface area will give a greater area for the reaction to occur, the energy of the particles does not change and the number of collisions will increase and therefore the frequency of successful collisions will increase per second.
how does the addition of a catalyst affect the rate of reaction
The addition of a catalyst will lower the activation energy required to start a reaction. More particles will have the required activation energy or greater, and so this will increase the number of collisions per second.
Experiments for the rate of reaction
1) Measuring the formation of a precipitate over time e.g. (disappearing cross or a colorimeter)
2) Measure the volume of a gas given off overtime you will need a gas syringe or an inverted measuring cylinder in water
3) you can measure the colour change over time (colorimeter)
4) You can measure the pH overtime using a pH probe
Maxwell Boltzmann distribution of energies, what does this graph show
It shows the energy of particles in a system at a given temperature
Maxwell Boltzmann distribution curve key principles
The area under the curve shows the total number of molecules
The most probable energy/mode is the peak of the curve
The mean is just to the right of the most probable energy
Only a few molecules have a high energy there is no maximum energy as the curve is asymptomatic
Very few molecules will react upon collision (have the activation energy or greater)
what is on the X and Y axes of the Maxwell Boltzmann distribution curve
on the X axes it is the number of molecules with energy
On the Y axes it is the collision energy
common mistakes of the Maxwell Boltzmann distribution curve
The area under the curve is not the same and doesn’t start at the origin
The graph should not touch the X axes as it is asymptomatic
The graph should not flick at the start
The graph should have a smooth peaking point (peak)
The effect of increasing temperature on the Maxwell Boltzmann distribution curve
Increasing the temperature will show a larger proportion of the particles that have the activation energy or greater. The peak will be lower than the original peak.
Make sure that the total number of molecules i.e. The area under the curve is the same in both curves As the number of molecules does not change.
The effect of increasing concentration on the Maxwell Boltzmann distribution curve (doubling the concentration)
The area under the curve will double as you are doubling the number of particles/molecules. This doubles the frequency of successful collisions.
Increasing the concentration will therefore increase the pressure as there are double the amount of molecules in a fixed/given volume.
