3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc
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when can dynamic equilibrium occur
in a closed system which is at a constant temperature
what is Le Chatelier’s Principle
if a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change
in a reversible reaction at equilibrium…
-forward and reverse reactions proceed at equal rates -the concentrations of reactants and products remain constant.
define dynamic equilibrium
state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in constant concentrations of reactants and products over time
what happens if you increase the concentration of a reactant
increase concentration of reactant = equilibrium tries to get rid of extra reactant = favours forwards reaction = equilibrium shifts right
what happens if you increase the concentration of a product
increase concentration of product = equilibrium tries to get rid of extra product = favours backwards reaction = equilibrium shifts left
what happens if you decrease the concentration of a reactant
decrease concentration of reactant = favour backwards reaction = equilibrium shifts left
what happens if you decrease the concentration of a product
decrease concentration of product = favours forwards reaction = equilibrium shifts right
what equilibria does changing pressure affect
equilibria involving gases
what happens if you increase pressure
increase pressure = equilibrium shifts to side with fewer gas molecules to reduce pressure
what happens if you decrease pressure
decrease pressure = equilibrium shifts to side with more gas molecules = increases pressure
what happens if you increase temperature
increase temp adds heat = equilibrium shifts in the endothermic direction to absorb heat
what happens if you decrease temperature
decrease temp removes heat = equilibrium shifts in the exothermic direction to try replace the heat
conditions for reaction to make ethanol from ethene and steam
• pressure of 60 to 70 atmospheres • temp of 300 degrees C • phosphoric acid catalyst
making ethanol from ethene and steam: exothermic or endothermic
exothermic
making ethanol from ethene and steam temperature
low temp favours forwards reaction (so more product) but low temp means slow rate of reaction so 300 degrees C is a compromise
making ethanol from ethene and steam pressure
high pressure favours forwards reaction and increases rate of reaction. pressure isn’t higher as this is too expensive
making ethanol from ethene and steam equation
C2H4 (g) + H2O (g) = C2H5OH (g) reversible
making ethanol from ethene and steam how much ethene reacts
small proportion of ethene reacts each time gases pass through reactor
making ethanol from ethene and steam what is done to increase how much ethene reacts
unreacted ethene is separated from the ethanol and recycled back into the reactor
making ethanol from ethene and steam how much ethene is converted to ethanol
95% of the ethene is converted into ethanol
making methanol equation
2H2 (g) + CO (g) = CH3OH (g) reversible
making methanol pressure
50-100 atmospheres
making methanol temperature
250 degrees C