Kinetics 3.1.5 (AS) Flashcards
what is the rate of reaction defined as
The change in concentration of a substance in unit time.
what is the equation to work out rate
rate = amount of reactant used or product made / time
What is collision theory
- reactions can only occur if the particles collide in the correct orientation
- they must also have minimum energy to collide known as the activation energy
what is the activation energy
the minimum energy which particles need to collide to start a reaction
what does the maxwell-boltzmann distribution show us
the energy in gas particles
why must the maxwell boltzmann graph start at the origin
No particles have zero kinetic energy
what’s on the y and x axis of the maxwell boltzmann graph
y axis : number of molecules
x axis : kinetic energy
what does the area under the curve of a maxwell boltzmann distribution represent
the total number of particles present
what does the peak of the maxwell boltzmann distribution curve represent
The most likely energy of a particle in a sample ( Emp) ( the mode)
what does the point on the right of the peak represent in a maxwell boltzmann distribution curve
the mean energy of the particles
where is the activation energy in a maxwell distribution curve
near the bottom , where it starts to plateau
what does the area under the activation energy of a maxwell boltzmann distribution mean
particles with energy greater than the activation energy can react
- only a few particles have energy greater than the Ea
why should the energy distribution of a maxwell boltzmann curve never meet the x axis
there is no maximum energy for molecules
where in a maxwell boltzmann curve do particles have low energy and why
Before reacting the Emp ( peak of the curve )
- Because collisions cause some particles to slow down
where in a maxwell boltzmann distribution curve do most particles move with moderate speeds
in between the emp and the mean energy
what would the maxwell boltzmann curve look like if you increase temperature
- the total area under the curve should remain constant because the total number of particles is constant
- lower peak
- wider
- Area under the Ea is higher
- curve shifts to the right
what would the maxwell boltzmann curve look like if temperature decreases
- curve shifts to the left
- peak is higher
- area under curve is the same
- area under curve beyond activation energy decreases
why do we get a faster rate of reaction when temperature is increased
They collide more frequently and more often with energy greater than the activation energy .
This results in more frequency of successful collisions
How do concentration and pressure increase rate
At higher concentrations and pressure there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective / successful collisions
What does the maxwell boltzmann distribution curve look like when we increase concentration
- shape of the curve does not change ( peak is at same energy )
so EMP and mean energy do not change - The curves will be higher
- area under the curves will be greater because there are more particles
how do catalysts increase the rate
catalysts provide an alternative route or mechanism with a lower activation energy .
If activation energy is lower , more particles will have energy higher than the activation energy
- higher frequency of successful collisions
how does the maxwell boltzmann distribution curve change when a catalyst is involved
activation energy shifts to the left
how can rate be measured in experiments
- how long it takes for precipitate to form
- amount of mass lost
- volume of gas produced
what is the experiment of how long it takes for a precipitate to form
- place a cross on paper and time how long it takes for the cross to disappear
- problem = this is difficult to know when exactly the cross disappears
- try to use the same observer to reduce errors
what is the experiment for the amount of mass lost
- for reactions that produce a gas
place reaction in balance and measure the mass loss as gas is lost - fairly accurate method however use a fume cupboard if gas is harmful or toxic
what is the volume of gas experiment
another way of measuring the rate of a gas is produced
- measure the amount of gas louder using a gas syringe
- measure this over a specified time
