How far? Flashcards
(32 cards)
What is kp?
the equilibrium constant for a gas phase reaction
What does a large kc value mean?
means the position of equilibrium lies to the right
what does a very small kc value mean?
position of equilibrium lies to the left.
what would a kc value of one suggest?
that the reaction lies half way between the reactants and the products
What happens to the number of molecules during reversible reaction? (equilibrium moles)
the total number of moles of substance is not conserved or constant (although the total number of atoms are conserved) e.g. the dehydrogenation of ethane to produce ethene and hydrogen
in a reversible reaction to her dies cincersin of the reactants into products result in?
the number of moles of products increasing and the number of moles of reactants decreasing. (opposite can also occur, if there is a mixture of reactants and products, or just products.
Given the change in one of the components of the mixture we can deduce all the others.)
when do we not need to work out the equilibrium concentrations?
if there are an equal number of moles on both sides (volumes cancel in Kc(because c=n/vx1000))
What is kc only affected by?
change in temp
If you have a mixture of gases (A, B, C, etc), how is the moles fraction of gas a worked out?
by dividing the number of moles of A by the total number of moles of gas
What symbol is the mole fraction of gas A and gas Bgiven?
XA
XB etc
What is the equation of type mole fraction of gas A?
XA = number of moles of gas A/total number of moles of gas
What is the partial pressure of one of the gases in a mixture,
the pressure which it would exert if it alone occupied the whole container
What symbol partial pressure of gas A often given?
PA
what is the total pressure of gases due to? (first relationship)
both molecules hitting the walls - in other words, the sum of the partial pressures.
what is the equation to work out PA?
Partial pressure- mole fraction of A (XA) x total pressure
What is partial pressure measured in?
ATM
What is homogenous equilibrium?
which everything in the equilibrium mixture is present in the same phase. In this case, to use Kp, everything must be a gas
when can the partial pressures of the everything be worked out?
if you allow the reaction to reach equilibrium
What do kc and kp always have provided you don’t change the temperature?
same temp
what is the format of kp?
same as kc except partial pressure is used instead of conc
What is the effect of temp on kc/kp?
inc temp shifts the equilibrium in the direction of the endothermic reaction
to absorb the heat energy (lowers or increases the reactant concentration)
Dec temp shifts the equilibrium in the direction of the exothermic reaction to release the heat energy and (lowers or increases the reactant concentration)
what happens because the reactants are on the bottom of the kc or kp expression (concentration)
reactant concentration increases, Kc/Kp decreases in magnitude.
If reactant concentration decreases, Kc/Kp increases in magnitude.
What happens if you change the concentration or pressure of an equilibrium mixture? (one mark)
Kc/Kp does not change
State and explain the what happens in a system when the conc or pressure of an equilibrium mixture changes-
- write kp expression
- when pressure is increased, pp of all gases will increase (denom/num will increase if there are more moles on one side
3.Le chateliers principe
4 what happens to kp after the shift -Denominator decreases and Kp is restored to its original value.
(numerator also increases but you don’t need to explain both changes)
