Ch19 Equilibrium Flashcards
What factors must be true for a chemical system to be in dynamic equilibrium?
- if the concn of R + P remain constant
- rates of forward + reverse reactions are equal
- it needs to be a closed system
What is Le Chatelier’s Principle:
Le Chatelier’s Principle states…….:
When a system in dynamic equilibrium is subjected to external change, the position of equilibrium will shift to minimise effect of that change.
What is the general Kc equation:
What is a homogenous equilibrium:
Homogenous eqm = all species in same physical state
Kc expression contains concn of all species
What is a heterogenous equilibrium:
Heterogenous eqm = species in different physical states
Kc expression only contains species in (g) or (aq) as concentrations of (s) and (l) are constant.
What do the different Kc values represent?
- Kc > 1 = product favoured eqm
- Kc < 1 reactant favoured eqm
What is the rule for units in Kc calculations?
Positive indices come before negative indices
RICE TABLES SHEET
What is the Kp constant used for?
- reactions only involving gases
- partial pressure is used instead of concn in eqm expression
- partial pressure is proportional to concn
Explain how to calculate mole fractions:
Explain how to calculate partial pressure:
What three factors does Le Chatlier propose affect eqm?
- If concn of species increase, eqm shifts in direction that reduces concn
- If pressure increases, eqm position shifts towards side with gaseous moles
- If temp increases, eqm position shifts in endothermic direction
- If temp decreases, eqm shifts in exothermic direction
What three factors does Le Chatlier propose affect eqm?
- If concn of species increase, eqm shifts in direction that reduces concn
- If pressure increases, eqm position shifts towards side with gaseous moles
- If temp increases, eqm position shifts in endothermic direction
- If temp decreases, eqm shifts in exothermic direction
What do these values of k mean for the position of eqm:
* K = 1
* K = 100
* K = 1x10-2
- K = 1- indicates eqm halfway between R +P
- K = 100 - indicates eqm well in favour of P
- K = 1x10-2 - indicates eqm well in favour of R
What happens to k at constant temp but other factors changing (conc, pressure, catalyst) and what happens to k if temp changes,
- At constant temp, k is constant, does NOT change despite changes to concn, pressure, prescence of catalyst
- If temp is changed, k does change value.
Explain how temp affects value of k when the forward reaction is:
* exothermic
* endothermic
Forward reaction = exothermic
* k decreases with increase in temp
* increase in temp decreases eqm yield of products
* position is shifted towards products
Forward reaction = endothermic
* k increases with temp increase
* increase in temp increase eqm yield of products
* shifts eqm towards products
How does a change in concentration affect the value of Kc
How does a change in pressure affect Kp constant:
How does a catalyst affect eqm constants (Kc, Kp)
- eqm constants Kc and Kp are unaffected by presence of catalyst
- Catalysts affect rate of chemical reactions, not position of eqm
- catalysts speed up both forward and reverse reactions equally
- eqm is reached quicker, but eqm position NOT changed.
