Kinetics
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- Created by: Hindleyc
- Created on: 17-06-18 10:43
What is the collision theory?
Reactions can only occur when collisions take place between particles having sufficient energy
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What is the energy needed for?
to break relevant bonds in one or either of the reactant molecules
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What is the minimum energy required?
Activation energy
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what is the activation energy?
Minimum energy which particles need to collide to start a reaction
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What is the ROR?
Change in concentration of a substance in unit time usual unit=mol/dm^3/s
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How do you measure reaction rate?
gradient of graph of concentration v time
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What is the initial rate?
Rate at start of reaction where it is fastest
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What can reaction rates be calculated from?
graphs of concentration of product or reactant
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How else do we measure reaction rate?
1/time- approximation of ROR as doesn't include concentration
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why can this be used?
We can assume that the amount of sulphur produced is fixed and constant
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What is the Maxwell Boltzmann distribution?
Energy distribution showing spread of energies that molecules of a gas or liquid have at a particular temperature
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Where should the energy distribution start?
At the origin/ go through it because there are no particles with no energy
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Why do a few have low energies?
Collisions cause some particles to slow down
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What is the Emp?
Most probable energy (not same as mean)
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Where is the mean energies of particles?
Not at peak of curve
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What does the area under the curve represent?
Total number of particles present
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What do most molecules have?
energies between the 2 extremes but distribution not symmetrical (normal)
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Why should the energy distribution never meet eh x-axis?
there is no max energy for molecules
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What do only a few particles have?
Energy greater than or equal to the activation energy
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How can a reaction go to completion if few particles have energy greater than the activation energy?
particles can gain energy through collisions
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What happens as temperature increases?
the distribution shifts towards having more molecules with higher energies
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What happens to Emp and mean energy at higher temps?
shift to higher energy values although number of molecules with those energies decreases
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What happens to total area under curve?
Remains constant as total number of particles is constant
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What do the molecules have at higher temperatures?
Wider range of energies
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What happens 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 collisions
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What effect does this have on curve?
Shape doesn't change,- peaks at same energy so Emp and mean energy don't change. Curves will be higher and area under curves greater because there are more particles
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What does this mean
More molecules have energy greater than Ea (although not a greater proportion)
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What will different volumes of same initial concentration have?
Same initial rate if other conditions are the same but will end at diff amounts
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The higher the conc/temp/SA...
The faster the rate (steeper gradient )
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How to compare rate?
Need to calculate/ compare initial moles of reactants to distinguish between different finishing volumes. e.g. the amount of product is proportional to the moles of reactant
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Effect of catalyst?
Inc ROR w/o getting used up. by providing an alternative route or mechanism with a. lower Ea
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What happens if Ea is lower?
More particles will have energy greater than Ea so there will be a higher frequency of effective collisions- reaction will be faster
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What is the effect of inc SA?
Causes successful collisions to occur more frequently b/w reactant particles and this will inc the ROR
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What can a reaction not take place unless?
A collision occurs between reacting particles
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What do not all collisions lead to?
Successful reaction
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What must energy for a collision b/w erecting particles exceed?
Min energy for reaction to occur
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Effect of inc Conc? aq
Inc no. reacting particles per unit volume therefore greater frequency of collisions- the more collisions there are the faster the ROR
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Pressure ? g
Same as Conc
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Temp?
Inc no. particles with energy greater than or equal to A.E higher temp means more particles with sufficient energy to react so more frequent collisions so faster ROR
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Other cards in this set
Card 2
Front
What is the energy needed for?
Back
to break relevant bonds in one or either of the reactant molecules
Card 3
Front
What is the minimum energy required?
Back
Card 4
Front
what is the activation energy?
Back
Card 5
Front
What is the ROR?
Back
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