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Module 3 - Chapter 10 - Rates of reaction I - Coggle Diagram
Module 3 - Chapter 10 - Rates of reaction I
Rate of reaction
Rate of chemical reaction - howfast a reactant is being used up/ how fast a product is being formed
Change in concentration of a reactant/ product in a given time
Fastest at the start of the reaction, concentration is highest
Rate slows down as the reaction proceeds cause the reactants are being used up and concentrations decrease
Once a reactant is used up, concentration stops changing and rate of reaction is zero
On a concentration-time graph, rate of reaction equals the gradient of the curve
Altering rate
Collision theory
Two reacting particles must collide for a reaction to occur
Effective collision leads to a chemical reaction
For a collision to be effective, particles must collide with correct orientation and particles must have enough energy to overcome the activation energy barrier
Concentration
Increasing concentration increases the rate
Number of particles increases, particles are closed together and collide more frequently
In a given time, there'll be more effective collisions and an increase rate
Probability of collisions occuring with greater/ equal activation energy increases
Pressure
Increasing pressure compresses the gas into a smaller volume
Concentration of molecules increases as the same number of molecules occupy a smaller volume
Closer gas molecules collide more frequently
More effective collisions
Temperature
Thermal energy transferred is coverted to kinetic energy
Increased movement means collisions occur more often and with greater energy
More effective collisions, rate increases
Surface area
Increases surface increases number of exposed reactant particles
There are more frequent, successful collisions, rate increases
Following reaction progress
Monitor the volume of hase produced at regular intervals
Monitor the loss of mass of reactants using balance
Volume of gas produced and mass loss are proportional to change in concentration of reactant/ produt
Gas collection
Place an inverted cyclinder in a trough of water and measure the initial water level
Once the reaction starts, measure the volume at regular intervals until the reaction is complete
Gas syringe can be used instead
Plot a graph of gas produced against time, to find the rate at a certain time, draw a tangent and find the gradient
Mass balance
Initial mass of flask and contents is recorded and then at regular time intervals
Reaction is compelte when mass is constant
Plot a graph of mass lost against time and draw a tangent
Catalyst
Catalyst is a substance that changes the rate of a chemical reaction without undergiong any permanent change itself
May react with a reactant to form an intermediate or may provide a reaction surface
Increases the rate by providing an alternative reaction pathway of lower activation energy
Types
Homogeneous
Sam physical state as the reactants
Catalyst reacts to from an intermediate and then breaks down to give the product and regenerates the catalyst
Heterogeneous
Different physical state from reactants
Usually solids in contact with gaseous/ in solution reactants
Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction take splace
After the reaction, product molecules leave the surface by desorption
Molecules are adsorbed onto an active site, they increase the proximity of molecules and weaken covalent bonds so reactions occur more easily
Transition metals
Variable oxidation states
Electrons are transferred to produce a reactive intermediate
Contact process - Uses vanadium oxide to speed up conversion of sulfur dioxide to trioxide
Substainability/ economic importance
Catalysts allow for reduced temperatures for industrial processes
Less energy is required, less electricity/ fossil fuels are used
Costs are cut, productivity increases
Autocatalysis
When a product acts as a catalyst for that reaction
Reaction starts slowly and speeds up as products form
Boltzmann distribution
Energy of moving particles
In a gas/liquid, different parrticles have difference amounts of energy so move at different speeds
Spread of molecular energies in gases is known as the Boltzmann distribution
Only a small proportion of molecules have more energy than the activation energy
Features
No molecules have zero energy
Area under the curve equals the number of molecules
Number of molecules with given energy on the y axis, and energy of the x axis
No maximum energy for a molecule- curve doesn't meet the x axis at high energy
Peak is the most probable energy of a molecule
Temperature
Increasing temperature increases the avergae energy of the molecules
Small proportion of molecules still have low energy, more molecules have higher energy
Graph is stretched over a greater range of values
Peak is lower on the y axis and further on the x (peak is at a higher energy)
Area under the curve is the same (number of molecules is the same)
Catalysts
Activation energy lowers
Greater proportion of molcules have an energy equal to/ greater than the lower activation energy
On collision, more molecules react to form products, causing a greater rate of reaction
Concentration, pressure and surface area
Doesn't change the energy of the indivdual particles
Shape of distribution doesn't change
