Rates. Flashcards
Rate of reaction calculation.
change in concentration/time.
Graph of reaction rate.
Steepest/fastest at start of reaction as each reactant at highest concentration
Slows as reaction proceeds as reactants being used up and concentration decreases
Once one reactant used up plateaus and no change in concentrations=ROR 0.
Collision theory.
For a reaction to be successful particles must collide with sufficient energy and proper orientation.
Effect of concentration on ROR.
Increased concentration of reactant=increase in ROR:
More particles in same volume
Closer together and collide more frequently
Will be more effective/successful collisions in a given time.
Effect of pressure of gases on ROR.
Increased pressure=higher ROR
More gas particles in same volume
Concentration of gas molecules increases as same number of molecules in a smaller volume
Closer together and collide more frequently
More successful/effective collisions in same time.
Role of a catalyst.
Increases rate of reaction:
Not used up in reaction
May react to form an intermediate or provide a surface where the reaction can take place.
How do catalysts work?
Provides alternative pathway for reaction via a lower activation energy.
Revise enthalpy profile diagrams.
Homogeneous catalysts.
Has the same physical state as the reactants.
Forms intermediate
Breaks down to give product
Regenerates catalyst.
Heterogeneous catalysts.
Has a different physical state from the reactants.
Reactant molecules absorbed(weakly bonded) to surface of catalyst
Where reaction takes place
After, product molecules leave surface of catalyst by desorption.
Benefits of catalysts.
Reduces temperature needs for reactions
Less electricity or fossil fuels used
Faster and less energy=lower costs
Less energy used=less pollutants w/ higher atom economies and less CO2 emissions= environmental sustainability.
The Boltzmann distribution.
Ea=activation energy
Shows amount of particles w/ high energy and low energy
Only small number of particles have above Ea.
No molecules have 0 energy
Area under curve=total number of molecules
No max energy for particle=does not meet x axis
Highest peak=average amount of energy/the energy most particles hold.
Effect of temperature on Boltzmann distribution.
Increase in temperature=average energy of molecules increases
More molecules have a higher energy
Stretched over a greater range of energy values
Some still have low energy values
Peak at higher energy but lower on y axis
Greater amount of molecules over Ea.
Effect of temperature on ROR.
Higher temperature=more molecules w/ energy at Ea or higher
Greater proportion of collisions will lead to a successful reaction
increasing ROR
Also more frequent collisions as faster molecules but less impact vs energy levels.
Effect of catalysts on Boltzmann distribution.
Provides alternate lower energy reaction route
by lowering Ea
Greater proportion of molecules have required energy
On collision, more molecules will react to form products=Higher ROR.
Effect of surface area of solid reactants on ROR.
Higher surface area=increased ROR
More particles are exposed to other reactants
More surface available for particles to collide
Greater chance of particles colliding
More successful collisions per given time.
