equilibria (I) Flashcards
what does Le Chatelier’s principle state
if a change is made to a system in dynamic equilibrium the position of equilibrium moves to counteract the change
what does it mean when a reaction is in dynamic equilibrium
- the rate of the forward reaction is equal to the backwards reaction
- the concentrations of the products and reactants remain constant
describe the effect of increase in temperature on a reaction in dynamic equilibrium
- an increase in temperature will favour the endothermic reaction, increasing the yield of the endothermic substance
describe the effect of decrease in temperature on a reaction in dynamic equilibrium
- equilibrium will shift to favour the exothermic reaction, increasing the yield of the exothermic substances
is the forward reaction endothermic or exothermic with an enthalpy change of +65 kjmol-1
endothermic
describe the effect of increase in pressure on a reaction in dynamic equilibrium
equilibrium will shift to the side with the fewest moles of gas (to release built up pressure)
describe the effect of decrease in pressure on a reaction in dynamic equilibrium
equilibrium will shift to the side with the greatest moles of gas
describe the effect of increase in concentration of products/reactants on a reaction in dynamic equilibrium
equilibrium will shift to the opposite side of the reaction
- (increasing conc of products will shift equilibrium in the direction of the backwards reaction)
- (increasing conc of reactants will shift equilibrium in the direction of the forwards reaction)
which type of system is affected by change in pressure, temperature and concentration
a homogenous system
do catalysts have an effect on the position of equilibrium and why
- no
- it will speed up the rate of the forwards and backwards reaction equally
(speeding up rate in which equilibrium is reached but with no effect on yield)
what are the conditions for making ethanol from ethene and water
- 60 atm pressure
- 300 degrees celsius
- phosphoric acid catalyst (H3PO4)
what is the equilibrium constant
Kc
How is Kc worked out
products/reactants (in square brackets to signify they are concentrations)
what is homogeneous equilibrium
both reactants and products are in the same state
what is heterogeneous equilibrium
some of the reactants and products are in different states
why arent solids and pure liquids included in Kc expression
their concentrations remain constant throughout the reaction
what is a high Kc value
where there are more products than reactants
what is a low Kc value
where there are more reactants than products
Haber process equation
N2(g) + 3H2(g) –> 2NH3(g)
what is continuous flow
an industrial process where reactants are constantly added and products are constantly removed
in terms of the Haber process what occurs with an increase in pressure
- equilibrium will shift to the right to the side with the smallest number of moles (2)
- the yield of ammonia will increase
in terms of the Haber process what occurs with an increase in temperature
- the position of equilibrium will favour the endothermic reaction and shift to the left
- decreasing the yield of ammonia
describe the conditions used in the haber process
- optimum conditions used for a high yield
why is it bad that Haber process requires a decrease in temperature
low temperature means low rate of reaction
why is it bad that the Haber process requires a high pressure
- high pressure expensive to maintain + equipment needed expensive
- H2 is very explosive under high pressures, it isnt safe
Describe the conditions used in the Haber process
- optimum conditions used for a high yield
- 450 degrees celsius temperature
- 200 atm pressure
- heterogeneous iron catalyst (in solid state)
why is a catalyst used in Haber process despite them having no effect on yield
due to use of continuous flow, this assures the reaction shifts forward with the catalyst
what happens with any unreacted hydrogen or nitrogen in the Haber process
they get re-cycled and react again
how is ammonia removed for continuous flow in the Haber process
ammonia is condensed then removed
where is nitrogen taken from in the Haber process
- taken from the atmosphere (78% nitrogen in atmosphere)
- economical as large quantity of it, that humans dont need
where is hydrogen taken from in Haber process
- comes from natural gas
- for example methane
reaction of methane and water to produce hydrogen
CH4 + 2H2O –> CO2 + 4H2
what is the aim of industrial and pharmaceutical processes
- maximise percentage yield
- make products as quickly as possible
- keep cost as low as possible
- have high atom economy (100% in Haber process as only desired NH3 formed)
