Unit 3 - Chemical Systems and Equilibrium Flashcards
Dynamic Equilibrium (definition)
State of balance WITH movement
-two opposing rxns taking place at equal rates
-NO net reaction
-involves microscopic changes, invisible. No observable changes
-reaction is never complete, for every forward rxn there is a reverse rxn, always in motion.
Definition of Equilibrium
the state of a rxn in which all the reactants and products have reached CONSTANT concentrations in a CLOSED SYSTEM
Conditions that apply to all Equilibrium systems
- rates of opposing changes are equal
- observable properties of system are constant (no change can be observed)
- can only be reached in a CLOSED system (does not allow input or escape of any component of system including energy)
- can be reached from either direction
Homogeneous and Heterogeneous Equilibrium
Homogeneous: rxn with reactants and products in the same phase/state (ex. all gases)
Heterogeneous: rxn with reactants and products in different phases/states; concentration of solids and liquids are constant so are not included in equilibrium expression
What is the purpose of ‘K’ (equilibrium constant)?
helps to predict the relative concentrations of reactants and products in an equilibrium system
What does it mean if K=1 (approximately)?
Concentrations of products and reactants are approximately equal at equilibrium
What does it mean if K»1?
reaction proceeds toward completion, to the right.
more products at equilibrium
What does it mean if K«1?
reaction proceeds toward the left.
more reactants at equilibrium
Reaction Quotient (Q) purpose?
allows us to predict if a rxn has reached equilibrium, and to determine which direction the rxn must proceed to reach equilibrium
What does it mean if Q>K?
rxn has to proceed to left
What does it mean if Q=K?
system is at equilibrium
What does it mean if Q<K?
rxn has to proceed to the right
Le Châtelier’s Principle
When a chemical system at equilibrium is disturbed by a change in a property (a stress), the system adjusts in a way that opposes the change/stress.
How will system react to concentration changes (increasing and decreasing), using Le Châtelier’s Principle?
Increasing: system will react by consuming the excess, shifting to opposite side of whatever was added.
Decreasing: system will react by producing to replace loss, shifting to the side of whatever was lost.
How will system react to temperature changes (cooled and heated), using Le Châtelier’s Principle?
Heated: shifts in direction that ABSORBS heat
Cooled: shifts in direction that PRODUCES heat, trying to “warm itself”
How will system react to pressure changes (increase and decrease), using Le Châtelier’s Principle?
{gases only}
if volume changes, pressure also changes (but opposite). System reacts to oppose the change by shifting to increase/decrease the number of gas molecules. If equal # of gas molecules on each side of equation, no change.
Pressure increase: volume decreases, # of gas molecules must decrease, shifts to side with less molecules
Pressure decrease: volume increases, # of gas molecules must increase, shifts to side with more molecules
Changes that do NOT affect the position of equilibrium
-Adding a catalyst, just speeds up fwd and rev reactions equally.
-Adding an inert (unreactive) gas, total pressure is increased but since its inert, it wont react with anything.
Molar Solubility Definition
concentration of the solution at its saturation point
