reaction rates and equillibrium Flashcards
what is a catalyst
a catalyst is a substance which increases the rate of a chemical reaction without undergoing any permanent change itself.
Extra notes on catalysts
The catalyst is not used up in the chemical reaction , the catalyst may react with a reactant to form a intermediate or may provide a surface on which the reaction can take place . At the end of the reaction the catalyst is regenerated .
How do catalysts work
By providing an alternative reaction pathway with a lower activation energy . This means that a greater proportion of the reactant molecules will collide with enough energy to cross the activation energy barrier and react .
What are the two types of catalyst
Homogeneous and heterogeneous catalysts
Is activation energy exo or endo
Activation energy is always endothermic
What is another word for physical state
Phase
What is a homogeneous catalyst
Here the catalyst is in the same physical state as the reactants . The catalyst forms an intermediate which then breaks down to give the product and regenerates the catalyst .
What is a heterogeneous catalyst
Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants eg. In a vehicle catalytic convertor
What is a heterogeneous catalyst
Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants . Eg in a vehicle catalytic convertor
What happens in a heterogeneous catalytic converter
Bonds formed to catalyst surface must be weak enough to allow adsorption and desorption to take place , but strong enough to weaken bonds and allow the chemical reaction to take place
What does a poison do
Binds to the surface but doesnt leave
What is a catalytic convertor
Heterogeneous, adsorption/desorption , three key reactions catalysed
What are the three reactions catalysed
The oxidation of carbon monoxide to carbon dioxide .
The reduction of nitrogen monoxide back to nitrogen
The oxidation of hydrocarbons to water and carbon dioxide
What is the equation for the oxidation of carbon monoxide to carbon dioxide
2CO(g) + O2(g) —> 2CO2(g)
What is the equation for the reduction of nitrogen monoxide back to nitrogen
2NO(g) + 2CO2(g) —> N2(g) + CO2(g)
What is the equation for the oxidation of hydrocarbons to water and carbon dioxide
2C6H6+15O2—> 12CO2+ 6H2O
What are the benefits of catalysts
-Lower temperatures and pressures required therefore reducing energy demand .
-different reactions can be used with better atom economy thus reducing waste
-lower production costs
-catalysts can be used to generate specific products
What are some examples of important industrial reactions reliant on heterogeneous catalysts
Making ammonia (Fe) N2+3H2–> 2NH3
Reforming (fuel improvement ) (pt or rh) c6h14 —> c6h12 +h2
Hydrogenation of alkenes (Ni) c2h4 + h2 —> c2h6
Making sulfur trioxide for sulfuric acid (v205) 2So2 + o2 —> 2so3
what is the general reversible reaction equation
aA+bB=cC+dD
what is the general equation for the equilibrium law
Kc = [C]c [D]d
[A]a [B]b
what is Kc in terms of reactants and products
Kc = products
reactants
what is equilibrium law
the exact position of equilibrium is calculated using the equilibrium law
what does the magnitude of Kc indicate
the magnitude of Kc indicates the extent of a chemical equilibrium . it indicates how far a reaction proceeds , not how fast
when K=1 what does this mean
indicates a position of equilibrium that is halfway between reactants and products
what does Kc>1 indicate
a position of equilibrium that is towards the products
what does kc<1 indicate
a position that is towards the reactants
Suggest two reasons why using a lower temperature is beneficial to the environment
Reduction in co2 emissions
Less energy use
What are the benefits of catalysts
Less co2 emissions as energy is saved
Reduce waste by allowing a different reaction to be used with a better atom economy
Catalytic converters reduce pollution
What is the definition for rate of reaction
The change in concentration of a reactant or product per unit time
What is the equation for rate of reaction
Change in concentration of reactant or product / time taken for the change to take place
What are the units for rate of reaction
Moldm^-3 s^-1
Where is the rate of reaction the fastest
T=0
What are the factors that can affect rate of a reaction
Catalyst, temperature, concentration, surface area , pressure
What makes a successful collision
Head on collision , more energetic reaction takes place
Orientation must be correct
how does increasing the concentration affect rate of reaction
increases rate of reaction as increases the number of molecules in the same volume , the particles are closer together leading to more frequent collisions
how does increasing the pressure affect rate
increasing the pressure of gaseous reactants means the same number of molecules occupy less volume so the molecules are closer together and so collide more often
what method can we use to measure the rate of reaction for an acid or base
ph changes by carrying out titrations
ph changes by using a ph meter/ probe
for reactions that produce gases what methods can we use to measure rate
change in volume or pressure
the loss of mass of reactants
for reactions that produce visual changes what can we observe to measure rate
the formation of a precipitate or a colour change
for reactions that involve changes in the amounts of ions , we can measure ….. to measure rate
changes in the electrical conductivity of the reaction
why does the boltsman curve start at the origin
because no molecules have zero energy
what does the total area under the curve in the boltsman distribution represent
the total number of molecules
what does the shaded area under the curve represent
the number of molecules with enough energy to react if they collide
why does the curve not meet the x axis
there is no maximum energy for a molecule .
at higher temperature what happens to the curve
peak (most probable energy) shifts to the right and down and shaded area increases as a greater proportion of collisions will lead to a reaction
what happens to the curve in the prescence of a catalyst
no effect on the distribution of energies . activation energy reduced and shifts to left
what happens at dynamic equilibrium
the forward and backward reactions continue at equal rates so the concentrations of reactants and products do not change
what is a closed system
a system isolated from its surroundings
what is the position of equilibrium
the relative quantitites of reactants and products . indicating the extent of a reversible reaction at equilibrium
what is le chateliers pricniple
when a system in dynamic equilibrium is subjected to change , the system reajusts itself to minimise the effect of the change and restore equiibrium
if concentration of a reactant is increased what will happen
more products will be formed until equilibrium is reached again
if concentration of a product is decreased what will happen
more reactants will react until equilibrium is reached again
if the temp of a system is increased what will happen
favour endo
what does an increase in pressure do
shift to side with smaller amount of gas molecules
What is Kc affected by
Only by temperature
Why is high pressure bad for high yield equations
Provides a safety risk
Why are higher temperatures not ideal for industrial processes
Higher temperatures increase energy costs
