unit 3 KA2 - controlling the rate Flashcards
(28 cards)
what must be controlled in industrial processes
reaction rates
what may happen if the reaction rate is too low in industrial processes
the process will not be economically viable
what may happen if the reaction rate is too high in industrial processes
there will be risk of explosion
what relationship may be used to perform calculations into reaction rate
the one between reaction time and relative rate with appropriate units
collision theory can be used to explain the effects of factors on reaction rates. what are these factors?
- concentration
- pressure
- surface area (particle size)
- temperature
- collision geometry
what can be used to show the energy pathway for a reaction
a potential energy diagram
what is meant by the enthalpy change
this is the energy difference between the products and the reactants.
when does the enthalpy value have a negative value
for exothermic reactions
when does enthalpy change have a positive value
for endothermic reactions
what is the activation energy
the minimum energy required by colliding particles to form an activated complex
how can activation energy be calculated
from potential energy diagrams
what is the activated complex
an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction
how do catalysts speed up chemical reactions
they provide an alternative reaction pathway with a lower activation energy
what can be used to show the effect of a catalyst on activation energy
a potential energy diagram
what is temperature
a measure of the average kinetic energy of the particles in a substance
what is the activation energy IN TERMS OF TEMPERATURE
the MINIMUM kinetic energy required by colliding particles before a reaction may occur
what can be used to explain the effect of changing temperature on the kinetic energy of particles and reaction rate
energy distribution diagrams
how can the effects of temperature and adding a catalyst be explained
in terms of a change in the number of particles with energy greater than the activation energy
why is the activation energy required to start a reaction
it breaks the bonds in the colliding particles
what are the two conditions to allow a reaction to occur
- correct geometry
- activation energy
why does an increase in particle size increase the reaction rate
as the surface area of a reactant increases, the area of contact between the reactants increases and this increases the rate of collisions between the reactant particles. there will therefore be more successful collisions and so the overall reaction rate will increase
why does an increase in concentration of the reactants increase the reaction rate
as the concentration of a reactant increases the reactant particles are pushed closer together which increases the rate of collisions. this gives rise to more successful collisions and results in the reaction rate to increase
why does an increase in temperature increase the reaction rate
temperature can be regarded as a measure of the average kinetic energy of particles in a substance. at higher temperatures particles have more kinetic energy and will therefore collide with greater force and more particles will have the required activation energy
in terms of bond breaking, state why a reaction is exothermic
in an exothermic reaction, the total energy for the bond breaking steps is less than the energy released in the bond making steps
