Kinetics Flashcards
What must particles do in order to react?
Collide with sufficient energy activation energy) and the correct orientation.
Do most collisions result in a reaction?
No
Define activation energy
The minimum energy required for particles to collide with, in order for a reaction to occur.
What is the effect of increasing temperature on rate of reaction? Why?
Increasing temperature = increased rate of reaction.
Much higher proportion of particles have energy greater than the activation energy = more successful collisions per second = increased rate of reaction.
What is the effect of increasing concentration/pressure on rate of reaction? Why?
Increased concentration/pressure = increase rate of reaction.
There are more particles in a given volume = more frequent successful collisions = increase rate of reaction
What is catalyst?
A substance which increases the rate of reaction but is not used up in the reaction.
How do catalysts work and how do they increase rate of the reaction?
Catalyst provide an alternative reaction pathway (one activation energy).
Low activation energy, so more particles have E >/ EA, so more frequent successful collisions, so increase rate of reaction.
How does increasing temperature change the maxwell Boltman distribution curve?
Total area under curve remains same as same number of particles.
Distribution shift more so molecules with higher energies.
EMP and mean shift to higher energies but few particles have these energies.
I.e. peak is lower onto the right.
Molecules have a wide range of energies done at lower temperatures.
More particles have energy greater than activation energy.
How do we measure rate of reaction with disappearing cross?
Reactant? Calculations? Equations?
(Sodium thiosulphate and hydrochloric acid)
Na2So3 + 2HCl —-> 2NaCl + So2 + H2O
Measure time taken for cross to be obscured in seconds using stopwatch.
1/time = rate of reaction
Approximate for rate. Though we do not consider concentration assume moles of sulfur produced is fixed and constant.
How does increasing concentration change Maxwell Boltman distribution curve?
Increasing particles increases number of particles per unit volume, increases the frequency of successful collisions.
Shape of graph remains same: same position of EMP and mean but covers higher as area underground is greater as more particles.
More molecules have energy greater than activation energy.
How does increasing pressure change Maxwell Boltzman distribution if temperature and volume are fixed?
pV=nRT, so at a constant V and T, for P to increase, n must increase.
Number of gas particles per unit volume has increased, thus concentration of particles has increased, frequency of successful collision increases.
Area under graph increases, and more molecules have energy higher than activation energy.
Why does increasing surface area increase the rate of reaction?
Frequency of successful collisions between reactant particles with greater energy than activation energy increases.
Define rate of reaction
The speed at which a reaction takes place.
What is a catalyst?
Catalysts are substances that speed up the rate of reaction by providing an alternative route with a lower activation energy. They can be heterogeneous or homogeneous.
They are not chamged or used up in the reaction themselves.
Explain how a high pressure increases rate of reaction
1) Particles are closer together
2) More successful collisions in a given period of time
