kinetics [P1] PAPER 2 Flashcards
how does a catalyst increase the rate of a reaction?
how does it alter the maxwell-boltzmann distribution curve?
• provides an alternative pathway with a lower activation energy
- nothing happens to the overall shape of the curve
- position of Ea shifts to the left (so more molecules have energy ≥ Ea)
define the term ‘activation energy’
the minimum energy required for a reaction to occur
why does the curve start at the origin?
no molecules have no energy
label the missing axis
number of particles/molecules
which letter represents the mean energy of the molecules?
C
which letter represents the most probable energy of the molecules?
B
what does the area under the curve represent?
total number of molecules/particles
why do most collisions between particles not result in a reaction?
the particles don’t have enough energy (they have energy less than the activation energy)
suggest why a small increase in temperature can lead to a large increase in the rate of reaction between colliding particles
MANY more particles with energy ≥ Ea (so much higher frequency of successful collisions)
what is the effect of increasing pressure/concentration on the rate of a reaction?
how does this change the maxwell-boltzmann distribution curve?
- more particles in a given volume
- more frequent successful collisions (in a given time)
- larger area under the curve (so more particles have energy ≥ Ea)
- most probable energy and activation energy still at the same points
- still starts at the origin
a nickel catalyst is used for a reaction - why is the catalyst more effective when coated onto an unreactive honeycomb?
• increases surface area
• increase in more successful collisions (in a given time on the surface of the catalyst)
how do you calculate the rate of a reaction at a specific time from a graph?
tangent from the line/curve of best fit at the point of the specific time
what is the effect of increasing/decreasing temperature on the rate of a reaction?
how does this change the maxwell-boltzmann distribution curve?
[INCREASE]
• molecules gain more kinetic energy and move faster
• more frequent successful collisions (in a given time)
[INCREASE]
• peak is lower and shifts to the right (so more molecules have energy ≥ Ea)
• still starts at the origin and (new) curve crosses original curve once
• same area under (new) curve
[DECREASE]
• peak is higher and shifts to the left (so less molecules have energy ≥ Ea)
• rest is the same as for increase
what must happen for two molecules to react with each other?
collide with energy more than or equal to the activation energy OR sufficient/minimum/enough energy
what must you ensure when drawing a maxwell-boltzmann distribution curve?
• start at origin
• never cross x-axis
what is a catalyst?
substance that speeds up a reaction but is chemically unchanged at the end
how could you identify a substance is a catalyst from chemical equations?
unchanged at the end of the reaction
OR the substance is re-formed
OR does not appear in the overall equation
why may a catalyst be hot when being used for a reaction?
to provide activation energy
why does the rate of a reaction decrease over time?
- fewer reactant particles that have energy ≥ Ea as they are being used up as the reaction progresses
- fewer successful collisions in a given time
- As concentration increases, temperature increases
- This increases the rate of reaction
- As there are more particles with energy ≥ Ea, more successful collisions occur in a given time
state the meaning of the term ‘rate of reaction’
change in concentration of a substance in a given time
at a given temperature of a sample of a gas, the average kinetic energy of all the molecules is ______
constant
