3.2.2 Extent of chemical reactions Flashcards
open vs closed
- open: matter and energy exchange
- closed: energy exchange only
reversible vs irreversible
- reversible: can occur in forward or reverse reaction since products can collide with each other to react again and form the reactants
- irreversible: can only occur in one direction
dynamic equilibrium
- rate of both forward and reverse reactions is equal (so concentrations don’t change) but the reactions have not stopped
- usually no observable change
- reaction is incomplete and both reactants and products are present
- reversible
equilibrium explained (N2, H2, NH3)
- forward: N2 and H2 molecules collide with each other and form NH3 so concentration of N2 and H2 decrease and frequency of collisions (rate of reaction) of forward reaction decreases but concentration of NH3 increases
- reverse: NH3 molecules start to collide and form N2 and H2 and reaction rate increases
- eventually both reactions proceed at same rate so concentration of all molecules remains constant
extent
- how much product formed when system reaches equilibrium
(e.g. strong acids react to a further extent but weak bases react to lesser extent since not as many products formed)
equilibrium constant K
a constant for a particular reaction at equilibrium at a particular temperature
reaction quotient reminders
- don’t forget units
- only include reactants/products in the same phase (i.e. gases ignore solides, aqueous ignore solids and water)
reaction quotient
proportion of reactants and products in a mixture
- indicates extent of reaction and equilibrium yield
values of K
K > 10^4 (only products are present)
K < 10^-4 (only reactants are present)
if inbetween, both reactants and products present
le chatelier’s principle
- if an equilibrium system is subjected to change the system will adjust itself to partially oppose the effect of the change and the system establishes a new equilibrium
position of equilibrium
relative amounts of reactants and products at equilibrium
adding reactant
- net forward reaction
- concentration of reactant spikes initially then decreases but still higher than original since position of equilibrium has shifted to the right
- concentration of products increases
Q<K
adding product
- net reverse reaction
- concentration of product spikes initially then decreases but still higher than original since position of equilibrium has shifted to the left
- concentration of reactants increases
Q>K
removing product (by reacting with another substance)
- net forward reaction
- concentration of product spikes down initially then increases but not as high as original
- concentration of reactants decreases
removing reactant (by reacting with another substance)
- net reverse reaction
- concentration of reactants spikes down initially then increases but not as high as original
- concentration of products decreases
decrease volume, increase pressure/concentration
- all concentrations initially increases
- then reaction proceeds to side with fewer moles of gas to partially oppose the change in the system and decrease concentration
increase volume, decrease pressure/concentration
- all concentrations initially decrease
- then reaction proceeds to side with more moles of gas to partially oppose the change in system and increase concentration
adding inert gas
- increases pressure but concentrations of reactants and products doesn’t change and position of equilibrium doesn’t change
dilution
- reduces concentration
- initially all concentrations decrease
- then reaction proceeds to side with more particles to partially oppose the system and increase concentration
temperature change
- temp increase: endothermic to absorb energy and decrease temp, K decreases
- temp decrease: exothermic to release energy and increase temp, K increases
- gradual change in concentrations
- rate will increase or decrease
catalyst
- increase rate of both forward and reverse reaction equally so no change in equilibrium position or constant
- but increase the rate which equilibrium is attained
