Equilibria yr 2 Flashcards
What is kc?
the equilibrium constant
What is the equation for kc for the reaction 2A + B = 2C + D
kc = [C]^2 [D]/ [A]^2 [B]
How do you calculate the units for kc?
same as you would for K in rate equation = cancel units in equation
What does homogeneous mean?
all products and reactants are in the same state
What does heterogeneous mean?
not all products and reactants are in the same state
What do you do if a substance in an equation is hetergeneous to the other substances in terms of writing the kc equation?
ignore it - not in kc equation
A(g) + B(s) = C(g) + D(g)
kc = [C] [D] / [A]
What 2 states are not included in the kc equation?
solids and pure liquids (water)
Why do you not include solids or pure liquids in the kc equation?
their concs remain constant
How can you work out the equilibrium concs?
ICE
Initial no. of mol
change in no of mol ( moles after reaction happened)
equilibrium no of mol / vol
What is the total pressure?
the total pressure in a reaction is the sum of all partial pressures of the individual gases
What is a mole fraction?
a mole fraction is the proportion (fraction) of a gas in a gas mixture
How do you calculate the mole fraction of a gas?
mole fraction of a gas = number of moles of gas/ tot number of moles in the gas mixture
or partial press of gas/ total pressure of mixture
How do you calculate partial pressure?
partial pressure = mole fraction x total pressure in a mixture
What is kp?
pressure equilibrium constant
What is used in the Kp equation instead of concs?
partial pressures of gases raised to the power of moles
What are the units for partial pressure?
KPa
What do you do when writing a Kp equation for a heterogeneous reaction?
only include gas substances
ignore solids, liquids and (aq)
What type of equilibria will Le chats principle only work in?
homogeneous equilibria
What happens to equilibria when you increase pressure?
equilibria will shift to the side of reaction that has fewer moles of gas
What happens to equilibria when increasing temperature?
shifts to the endothermic direction
What is the effect of temperature on the value of Kp?
if temp causes equil, to shift to right = kp increases
it temp causes eqil. to shift to left = kp decreases
How does pressure affect Kp?
changes pressure does not affect the value of Kp
What affect does adding a catalyst have on Kp and Kc?
no effect on the value of Kp and Kc = it speeds up the rate at which equilibrium is established
What are the affects of changing temp on kc?
temp change causes equil to shift to right = Kc increases
temp change causes equil to shift to left = kc decreases
What is the affect of changing concs on the value of Kc?
value of Kc is unaffected
What is equilibrium?
a reversible reaction in a close system is at equilibrium when the forward and back rates are equal
What are 3 methods for measuring the change in conc?
change in absorption of light - if substance is coloured
change in pH - acid/ alkali
titration
What does a larger kc and kp value mean?
the equilibrium is further shifted to the right
What happens to the value of kc increasing temp of a exothermic reaction?
equil shifts to left
kc decreases
What happens to the value of kc increasing temp of a endothermic reaction?
equil shifts to the right
kc increases
