Kinetics Flashcards
Activation energy is:
The minimum amount of energy needed for a reaction to occur
Accorsing to collision theory, a reaction can only take place if:
Particles collide with the minimum activation energy and in the correct orientation
Compare activation energies
Reactions with low Eas take place easily. Ones with high Eas do not, since they require extra energy e.g. from heat.
What is the rate of a reaction?
The change in unit concentration of a substance in unit time.
What happens when you increase the concentration in a reaction?
Increase the number of particles per unit volume, so particles are closer together, so reaction is faster because more frequent SUCCESSFUL collisions
What happens when you increase the pressure in a reaction?
More particles in the same unit volume, so particles are closer together, so more frequent successful collisions per unit time
What happens when you increase the temperature of a reaction?
More particles have energy greater than the activation energy, so more frequent successful collisions
What happens when you increase the surface area?
Smaller particles have a higher surface area to volume ratio, so more frequent successful collisions
How can you increase surface area?
Cutting
Adding ridges
Adding holes
Turning into powder
What is a catalyst?
Something which speeds up the rate of a reaction without being chemically used up.
How does a catalyst increase the rate of a reaction?
By providing an alternative reaction pathway with a lower activation energy
Describe the Maxwell-Boltzmann distribution
The Maxwell-Boltzmann distribution is a graph that shows the distribution of the kinetic energies of molecules of a gas at certain temperature (GAS ONLY)
State and explain the key parts of a Maxwell-Boltzmann distribution graph
Emp = most probable energy (bottom to highest point on the graph)
Emean = mean energy
Ea (activation energy) = molecules after the line have energy greater than the activation energy
Area under the curve = total number of molecules
Why can reactions reach completion?
Particles can have energy greater than the activation energy to react.
Even if a few particles have energy greater than the activation energy, the reaction can reach completion as the molecules transfer energy during collisions.
What is the effect of CHANGING the temperature on the Maxwell-Boltzmann curve?
Rate of reaction increases, so particles have more energy, so many more particles have energy greater than the activation energy, so the shape of the Maxwell-Boltzmann distribution changes.
