1.5 Kinetics
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What is the definition of Rate of Reaction?
Measure of the change of the concentration of products or reactants over time
What is the definition of collision theory?
That for a reaction to take place two particles must collide with enough energy to break the bonds
Why do collisions often not result in reactions?
• Not enough energy • Wrong orientation of molecules
What factors affect the rate of reaction and why?
Increasing temperature- Increases speed of the molecules so increases collisions Increasing concentration- More particles in same volume Increasing pressure- PArticles are closer together Increasing surface area- More surfaces available for reaction
In what ways can rate be measured?
• Time taken for precipitate to form (disappearing cross) • Volume of gas produced over time • Mass change overtime
What is the Maxwell Boltzmann distribution?
The distribution of energy amongst particles
Why does the Maxwell-Boltzmann graph start at the origin?
No particles have zero energy
What does the area under the graph in the Maxwell Boltzmann distribution show?
The total number of particles
What is the definition of activation energy?
The minimum amount of energy required for a reaction to take place
What is the difference between average energy and most probable energy on a Maxwell Boltzmann graph?
Average energy is the mean energy of the particles and is around the middle of the x axis and most probable is the energy at the peak with the most particles
Why do exothermic reactions not spontaneously occur in room temperature?
Activation Energy
What is the effect of temperature on the reaction curve?
• Lower and moves to right • Number of particles with very high energy increases • Area under the curve remains the same
What is the effect of high concentration on the reaction curve?
• Curve is higher and move to the right
Why does the reaction curve plateau?
Limiting reactant has run out so the rate is at zero
Why do some particles have very low energies?
Collisions cause molecules to lose energy
What is the definition of a catalyst?
Substances that affect the rate of reactions without being chemically changed
How do catalysts work?
Provide a different pathway with a lower activation energy Means more particles are at a high enough energy to react
What is a catalytic converter used for?
To reduce number of polluting gases produced by cars
How do catalytic converters work and give equations?
• Large surface area with honeycomb shape made of ceramic and coated with platinum less of the expensive metals needed CO+NO2 —> N + CO2 CxHx + NO —> N + CO2 + H2O
How do catalytic conversion reactions work?
• Adsorption- gases form weak bonds with metal atoms holding gases in right position to react • Desorption- Products break away from metal atoms freeing up catalyst surface
Why is the strength of bonds critical in catalytic conversion?
• Strong enough to hold gases in place • Weak enough to easily release products
Why is a honeycomb/ powder structure used in catalysts?
• Greater surface area • More successful collisions as more reactant surface is exposed • Rate increases without need for high pressures/temperature