Kinetics Flashcards
define collision theory (4)
- collision theorystates that for a chemical reaction to take place the particles need tocollidewith each other in the correctorientationand with enoughenergy
- the more succesful collisions = faster rate of reaction
what is the activation energy barrier
- means that bonds need to be broken before new ones can form.
- minimum energy required to break bonds and cause a chemical reaction
Give exaples of fast reactions and slow reactions
- Fast reactions: combustion of methane, reaction of sodium in water
- Slow reactions: rusting, digestion of food in gut
What is reactions rate
the speed at which reactants are converted into products in a chemical reaction
How is Rate of reaction calculated and what are the units
change in con/ change in time
moldm-3s-1
What does the maxwell Boltzmann distribution graph show
Shows how the speeds (and hence the energies) of a mixture of moving particles varies at a particular temperature
What does the assymetrical shape of the Maxwell Boltzmann diagram show
- Most particles have moderate energies
- A few have very high or very low energies
- The area under the curve represents the total number of particles present
- There is no maximum energy (the line does not cross the X axis – only at ‘infinite energy).
- Shaded area (after minimum Ea is reached) shows the proportion of particles with enough energy to collide effectively
What factors affect rate of reaction
- temp
- conc
- pressure
- catalyst
- surface area
What effect does temperature have on the RoR referencing the graph
- Curve gets broader and flatter due to a greater spread of values
- Total area under curve does not change = Total number of molecules in the system at that instant have not changed
- More particles with energy exceeding the activation energy
- Total number of molecules in the system at that instant have not changed – just the proportion with E > Ea
- Incnsreased kietic energy, greater collision rate, greater proportion of successful collisio
What effect does concentration have on the rate of reaction
- Increasing concentration increases rate
- More particles per unit volume
- More chance of a collision
- More successful collisions
What effect does pressure have on the rate of reaction
- Increasing pressure increases rate
- Particles are closer together
- Frequency of collisions increases
- More successful collisions
what effect does particle size have on RoR
- Rate increases as particle size decreases
- Smaller particles have greater surface area
- Increased frequency of collisions
- More successful collisions
Whats the effect of catalyst on the RoR and on the diagram
- lowers the activation energy
- more moecules with an excess of activation energy
- increased Rate of Reaction
what is the activated complex/ transition state, and describe the transition state theory
- the species that lies at the energy peak
- Transition state theory proposes that the activated complex is an intermediate arrangement that molecules go through, however it cannot be physically isolated and studied
whats the importance of studying rates of reaction
- Improve (optimise) the rate of production of a chemical
- Gain insight into the mechanism of a reaction
- Understand processes occurring in the environment
- Understand processes occurring within biological systems
- Assaying substances within body tissues
describe discontinuous methods to determine RoR
Destructive: Many separate experiments with different starting conditions: one reading per experiment
* Very difficult to measure the concentration at an exact time
- Especially in solution
- Can remove a product or stop the reaction
- e.g. by flash freezing or adding an inhibitor
- need many trials and can’t be sure exactly when the reaction stopped!
describe continuous methods to measure RoR
- Use physical techniques and don’t interfere with the progress of reaction
- e.g. by measuring the loss of reactant, formation of a product, change in colour intensity, pH etc…
- easier but less reliable
- only one experiment occuring eith many readings as experiment goes on
compare continuous and discontinuous methods
- continuous: only one experiment with many readings as the experiment goes on
- discontinuous: Many separate experiments with different starting conditions: one reading per experiment
what are some common methods of measuring rates of reactions
- loss of mass
- Measuring volume of gas
- colour intensity
- formation of precipitate
- pressure change
- conductivity
- Change in PH
what are the steps to calculating reaction rates from mass lost graphs
- Plot a graph of Mass lost against time
- Draw a tangent to the curve at t=0 (red line) This is the initial rate
- Calculate the rate from the gradient of the tangent
rate from the gradient
= y/x
- To calculate the rate at a specific time use the same tangent method but draw the tangent to represent the slope of the line at that time point ( orange line at 100s)
