Chem Unit 2 (Kinetics)) Flashcards
Rate of Reaction?
change in concentration / time
Affected by concentration?
There’s more particles in the same solution so more successful collisions with the necessary energy to react.
Affected by temperature?
The particles have more kinetic energy so move faster, leading to mroe successful collisions with the necessary energy to react.
Affected by particle size?
The smaller the particles, the large the surface area within which the particles can react so more successful collisions with the necessary energy to react.
Collision Theory?
particles in a gas are in constant motion, colliding with eachother.
These collisipons don’t all have the necessary energy to react. (e.g. 02 and N02 in air).
head-on collisons are more likely to cause a reaction than collisions at an angle and parrticles with more spped are more likely to cause collisons with suffiecnt energy to react.
Activation Energy?
Particle have to collide with sufficent combined kinetic energy to produce a reaction
This energy is needed to brerak the existing bonds and form the new ones in products.(transition state)
Colliding particles with insufficent energy just bump off each other.
Maxwell Boltzmann distribution of energies:
Small fraction of molecules have low energy ( (move slowly)
Small fraction of molecules have high energy (move quickly) - these particles ahve an energy equal or greater to the activation energy (E>Ea)
Most have an energy somewhere in the middle
Fraction of molecules ( y axis) and Energy ( x axis)
Effect of temperature on the rate of reactionL
More kinetic energy>more successful collisions>more particles with an energy (E>Ea) shaded area is higher
peak moves DOWN and to the RIGHT
total area under the curve stays the same because the volume is the same.
With a large temperature difference the difference between the number of particles with E>Ea is bigger and the difference between the peaks (maximum proportion of molecules) is going to be bigger.
Why does the E>Ea never go to 0?
Because particles can never have 0 energy.
10K rise in temperature (Kinetic graphs)
Peak move to the right but ONLY SLIGHTLY DOWN
The E>Ea particles are going to approximately double
Effect of concentration (Kinetics graph)
Concentration of the reactant decreases
Concentration of the product increases.
The rate of reaction at any given instant in a graph is given by the gradient/slope of the curve at that given instant.
How do you work out the rate of reaction from a concentration/time graph?
1) Plot the graph
2) Draw the curve
3) Draw a tangent on the specific bit of the curve (straight line following the shape of the curve)
4) Draw a hypotenuse triangle linking the tangent up with two straight lines.
5) Read off the change in concentration (on the y axis)
6) Read off the change in time (on the x axis).
Do change in concentration / time
What does a constant temperature have on the concentration/time realationship
If the temperature stays constant, the concentration the rate of reaction will also increase.
Concentration of gasses?
Increasing the pressure will increase the concentration of particles in the same volume and increase the number of successful collisions with sufficient energy to react.
