Module 3 Section 2 - Dynamic Equilibrium Flashcards
What is dynamic equilibrium?
The rate of the forward reaction is equal to the rate of the backwards reaction. The concentrations of the reactants and products remain constant and this can only happen in a closed system.
What is Le chatelier’s principle?
If there’s a change in concentration, pressure or temperature, the equilibrium with move to help counteract that change
How does concentration affect equilibrium?
1) if you increase the concentration of a reactant, the equilibrium counteracts this change by making more product so equilibrium shifts to the right.
2) if you increase the concentration of products, the equilibrium counteracts this change so more reactant is produced. The equilibrium position shifts to the left.
How does pressure affect equilibrium?
1) increasing the pressure shifts the equilibrium position to the side with fewer gas moles to reduce the pressure.
2) decreasing the pressure shifts the equilibrium to the side with more gas molecules. This raises the pressure
How does temperature affect equilibrium?
1) increasing temperature shifts the equilibrium position in the endothermic direction to absorb heat.
2) decreasing the temperature removes heat and so favours the exothermic direction to try and replace heat.
How do catalysts affect the position of equilibrium?
Catalysts have no effect on the position of equilibrium. They speed up the forward and reverse reactions by the same amount, they do not increase yield just allow equilibrium to be reached faster.
What is the equation for the formation of ethanol from ethene and steam?
C2H4 (g) + H2O <-> C2H5OH
What are the conditions for the reaction of ethene and steam?
1) ethanol is produced by a reversible exothermic reaction
2) 60-70 atmospheres
3) 300 degrees Celsius
4) phosphoric acid catalyst
Why are the conditions of the reaction of ethene and steam a compromise?
1) as the reaction is exothermic, lower temperature would increase the yield but the reaction rate would be too slow so 300 degrees is a compromise for maximum yield and faster reaction rate.
2) higher pressures favour the forward reaction so 60-70 atmospheres is used, as it increases reaction rate and yield. However increasing pressure more would be dangerous and expensive, so a compromise is used to maximise yield and minimise costs.
What is equilibrium constant?
It gives you an idea of how far to the left or right the equilibrium is
General equation for equilibrium constant?
Reactant / products
number in equation used as powers
How does the value of Kc show the equilibrium position?
1) the larger the value of Kc, the further to the right equilibrium lies, so more products relative to reactants.
2) the smaller the value of Kc, the further to the left equilibrium lies, so more reactants relative to products.
What are the two ways to investigate equilibrium position?
1) changing temperature
2) changing concentration
How to investigate equilibrium position by changing temperature?
Equation
2NO2 (g) <-> N2O4 - the forward reaction is exothermic / backwards reaction is endothermic
1) place two sealed tubes containing the equilibrium mixture in water baths, one cold and one warm water and observe the colours of the mixture.
2) in the warm water, the endothermic reaction is favoured, so equilibrium position shifts to the left, so more NO2 is produced. This changes the colour to a darker brown.
3) in the cold water, the exothermic reaction is favoured so equilibrium position shifts to the right so more N2O4 is made. This means the tube will lose colour as it is a colourless gas.
How to test equilibrium position by changing concentration?
Equation - mixing iron nitrate and potassium thiocyanate produce iron thiocyanate
Fe3+ + 3SCN- <-> Fe(SCN).
Fe3+ is yellow, SCN is colourless and Fe(SCN) is blood red. The equilibrium mixture is a reddish colour.
1) If you add more iron nitrate (Fe3+), the mixture turns a deep red colour
2) If you add more potassium thiocyanate (SCN-), the mixture turns a deep red colour
3) If you add more iron thiocyanate (Fe(SCN)) , the mixture turns a yellow colour
4) keep one test tube as a control that is just in equilibrium
