Rate of reactions Flashcards
Why must reaction rates be controlled in industrial processes?
If the rate is too low then the process will not be economically viable; if it is too high there will be a risk of explosion.
Relative rate calculation
Rate = 1/time units is S-1
Temperature
The measure of the average kinetic energy of the particles in a substance.
Energy distribution diagrams
Used to explain the effect of changing temperature, concentration, use of a catalyst.
Energy diagrams change in temperature
Stretch out line and flatten it so it goes further to the right if increased.
Make it go higher and further to the left if decreased.
Explanation of increased temperature on rate of reaction.
The kinetic energy of the molecules increases; more molecules have energy greater to the activation energy; the rate of reaction is increased.
Energy diagrams change in concentration.
Increase height of line in diagram as there are more particles present so more collisions occur. If concentration is increased.
Decrease height of line in diagram as less particles present so less collisions occur. If concentration decreased.
Explanation of increased concentration on rate of reaction.
With increased concentration; there are more particles present; more molecules have energy greater than the activation energy; the rate of reaction is increased.
Energy diagrams when catalyst is used.
Move line further to the left when catalyst used as more particles have energy past activation energy.
Move line further to the right when catalyst Is not used as less particles have energy past activation energy.
Explanation of catalyst on rate of reaction
With a catalyst; the activation energy required by the reactants decreases; more molecules have energy equal or greater to the activation energy; the rate of reaction is increased.
How does a catalyst increase rate of reaction?
It provides an alternative reaction pathway with a lower activation energy.
They work by forming temporary bonds with reactants, causing the bonds within the reactants to weaken- this lowers the activation energy.
Effect of particle size on rate of reaction
Powdered solids react faster than lumps. Since it is only the particles on the surface of a solid that can react (since they are exposed).
Breaking up solids into smaller pieces exposes more surfaces and hence more particles are available to react.
