Flashcards in Module 5: Chapter 19 (Equilibrium) Deck (19)
What is meant by the term dynamic equilibrium?
occurs when the rates of the forwards and the backwards reactions are equal and the concentrations of reactants and products no longer change (in a closed system).
Kc = ....?
[products] / [reactants]
What is heterogeneous equilibria?
Heterogeneous equilibrium contains equilibrium species in at least two different physical states or phases
The general rule is to not include concentrations of solids or pure liquids as their conc is constant - only include species that are (g) or (aq)
What is homogeneous equilibria?
A homogeneous equilibrium contains equilibrium species that all have the same state or phase (e.g. all gases)
What is Kp?
Kp is an equilibrium constant written in terms of the partial pressures of gases where the partial pressure of a gas is proportional to its concentration in a mixture of gases.
Mole fraction = ... = ... ?
mole fraction = volume of gas / total volume of gas = number moles of gas / total moles of gas
What is partial pressure?
Partial pressure = the pressure that a specified gas contributes to the total pressure.
What is the equation for partial pressure?
Partial pressure = mole fraction of the gas x total pressure
What is Kp and how does it differ from Kc?
The equilibrium constant Kp replaces concentrations of gases with partial pressures.
Square brackets must NOT be used! Only gases in expression
Why do endurance athletes like to train at high altitude?
- Total air pressure falls rapidly with altitude
- The oxygen dissolving ability of blood is directly proportional to the partial pressure of oxygen breathed in. The lower pressure at 5500m would lower the oxygen uptake of normal blood to 100cm3.
- Over time at this altitude the body can produce extra haemoglobin to increase the oxygen carrying capacity of the blood. By training at high altitude athletes can legally increase the oxygen carrying capacity of their blood. Back at normal altitudes this gives a competitive advantage in long distance running events.
What does the size of Kc indicate?
The size of the equilibrium constant K (either Kc or Kp) indicates where the position of equilibrium lies.
- K larger than 1 means the equilibrium position lies towards the product side (right).
- K smaller than 1 implies the equilibrium position lies towards the reactants side (left).
What factors change the value of K?
Changing concentration, pressure or adding a catalyst will NOT change the value of K.
The equilibrium constant will only change if the temperature changes.
What does adding a catalyst do to the value of K?
If a catalyst is added, the forward and reverse reactions both experience the same increase in rate (as the activation enthalpy is decreased by the same amount for each) so the equilibrium position is NOT changed but is reached more quickly.
Kp = ...?
p(products) / p(reactants)
What happens to the value of K when the forwards reaction is exothermic?
- K decreases with increasing temp
- raising temp decreases the equilibrium yield of products
What happens to the value of K when the forwards reaction is endothermic?
- K will increase with increasing temp
- raising temp increases equilibrium yield of products
Change in pressure = fewer moles of gaseous products
ratio of products to reactants < K
increasing pressure will increase products and decrease reactants
equilibrium shifts to the right
Change in pressure = more moles of gaseous products
ratio of products to reactants > K
increasing pressure will decrease products and increase reactants
equilibrium shifts to the left