Chemical equilibria and Le Chatelier's principle Flashcards
What does it mean when we say a reaction has reaction dynamic equillibrium?
- Forward and reverse reactions proceed at equal rates.
- The concentrations of reactants and products remains constant.
True or False
We would say a reaction has reach dynamic equillibrium when you have the same AMOUNT of products and reactants.
- False. The amount of products/ reactants will be different to each other but their concentration/ amounts will remain CONSTANT each!!
True or False
Equilibrium can be reached when a beaker (with reaction) doesn’t have a lid on top of it.
- False.
- Equilibrium cannot be reached here, because product will escape from the beaker.
- Equilibrium can only be reached in a closed system.
What are homogenous reactions?
- Homegenous reactions are where all the reactants and products are all in the same state. Ie. solid/ gas/ liquid.
What is Le Chartelier’s principle?
- If homogenous reaction at equilibrium is subjected to change in temperature, pressure or concentration, the position of equilibrium will shift to counteract that change.
What happens to conc of reactants/ products when:
- Equilibrium position shifts to left
- Equilibrium position shifts to right?
- Left: conc of reactants increases.
- Right: conc of products increases.
What will happen in this reaction below when:
- we increase the concentration of H2.
3H2 (g) + N2 (g) (reversible arrow sign) —> 2NH3(g)
Why is it significant that all reactants/ products are in the same state?
- The equilibrium position will shift to the right to use up/ reduce conc of H2 - more NH3 will be produced.
- Significant because this idea only works in homegenous reactions.
True or False
A catalyst will cause the equilibrium position to shift to the right, producing more products.
- False.
- A catalyst does not affect the position of equillibrium.
- Will speed up rate of forward/ backward reaction equally.
- It will speed up the RATE at which equillibrium is reached, no effect on yield.
What will happen in this reaction below if we:
increase/ reduce the pressure at homegenous equilibrium?
3H2 (g) + N2 (g) (reversible arrow sign) —> 2NH3(g)
- Increase pressure: equilibrium will shift to side with fewer no moles of gas to reduce pressure (ie. to the right here.) - More NH3 produced.
- Reduce pressure: equilibrium will shift to side with more no of moles of gas to increase pressure (ie. to the left here.) More N2 and H2 are produced.
What can Le Chartelier’s principle be used to predict?
- Le Chatelier’s principle can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions
What will happen in this reaction below if we:
increase/ decrease the temperature at homegenous equilibrium?
3H2 (g) + N2 (g) (reversible arrow sign) —> 2NH3(g)
∆H = -415kJmol-1
- Increase temp: equilibrium position will shift in endothermic direction (ie. in this case, to the left) to reduce the temp. More N2 and H2 produced.
- Decrease temp: equilibrium position will shift in exothermic direction (ie. in this case, to the right) to increase temp. More NH3 will be produced.
In industry, why does a compromise between pressure and temperature sometimes need to be made?
- Because sometimes increase in temp may decrease equilibrium yield and pressure increases equilibrium yield (and vise versa.)
What does the graph for concentration of reactant against time (for reversible reaction) look like? Why?
- Inverse proportion curve.
- Initally reactants are used up quickly (in forward reaction) but then slow as their concentration is used up.
Image of curve in folder for chemical equilibria
What does the graph for concentration of product against time (for reversible reaction) look like? Why?
- Curve shows increase and then plateus.
- Initally reactants are reformed (from products) slowly but then speed up as the concentration of product increases (from the forward reaction.)
Image of curve in folder for chemical equilibria
