10 - Reaction rates and equilibrium Flashcards
rate of a chemical reactant
measures how fast a reactant is being used up of how fast a product is being formed
when us a collision effective
- particles collide with correct orientation
- particles have sufficient energy to overcome the activation energy barrier of the reaction
increasing concentration affect rate of reaction
- ROR increases
- Increase in particles of the same volume, means they are closer together and collide more frequently. Therefore in a given time there is more effective collisions
increasing pressure of a gas affect ROR
- ROR increases
concentration of gas molecules increases as the same number of molecules occupy a smaller volume - molecules are closer so more frequent collisions and more successful collisions
how to measure the progress of a reaction
- monitor the removal of a reactant
- following the formation of a product
methods to determine ROR of gases
- monitor the volume of gas produced at regular time intervals
- monitor loss of mass of reactants using a balance
catalyst
a substance that changes the ROR without undergoing permanent change
- catalyst is not used up in the reaction
- catalyst may react with a reactant to form an intermediate or provides a surface for the reaction to take place
- catalyst is regenerated
types of catalyst
Homogeneous
Hetergeneous
Homogeneous
- has the same physical state as the reactants
- it reacts with the reactants to form an intermediate, it then breaks down to give the product and regenerates the catalyst
examples of reactions with a a homogeneous catalyst
1) making esters with sulfuric acid as a catalyst
CH3COOCH(l) + C2H5OH(l) -> CH3COO2H5(l) + H2O(l)
2) ozone depletion where Cl’ radicals as catalyst
2O3(g) -> 3O2(g)
Hetergeneous catalyst
has a different physical state to the reactants
- they absorb the reactant molecules onto the surface of the catalyst, where the reaction takes place
- after reactions, the product molecules leave the surfaces of the catalyst by deabsorption
example of heterogeneous catalyst
-Fe in the Haber process
- Ni in the hydrogenation of alkenes
catalysts- sustainability and economic importance
- reduces temp needed for reactions therefore the energy requirements
- less electricity or fossil fuels used, which can cut costs and increase profitability
axis on Boltzmann distribution
y= number of molecules with a given energy
x= energy
features of the Boltzmann distribution
- no molecules have zero energy- curve starts at origin
- area under the curve is equal to the total number of molecules
- there is no maximum energy for a molecules- so curve does not meet x axis
Boltzmann distribution and temperature
- as temp increases average energy of the molecules increases
- a small proportion of molecules have low energy and more molecules have higher energy
- graph is stretched over a greater range of values
- peak of graph is lower on the y-axis and further along the x-axis
-> greater proportions of collisions lead to a reactions as more molecules have energy greater than or equal to the activation energy
Boltzmann distribution and catalysts
- provides an alternative reaction with a lower Ea
- so Ea with catalyst has a greater proportion of molecules with energy equal to it more than the Ea without catalyst
dynamic equilibrium
- rate of forwards reaction is equal to the rate of the reverse reaction
- the concentration of reactants and products do not change
when will a reaction reach equilibrium
in a closed system
le chatelies principle
when a system in equilibrium is subjected to an external change the system readjusts itself to minimises the effect of that change
what does the value of Kc tell us
=1 indicates the position of equilibrium is halfway between reactants and products
> 1 position is more towards the products
<1 position of equilibrium lies towards the reactants
