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
Common Ion Effect
in a saturated solution, the addition of either ion from another compound will shift equilibrium.
The presence of a common ion DECREASES the SOLUBILITY of an ionic compound
Predicting if Precipitate will Form
if concentration of ions is greater than its molar solubility: Qsp>Ksp, rxn shifts to the left resulting in precipitation
Arrhenius Acid (definition, example)
substance that ionizes in water to produce H+ ions
ex: HCl
Arrhenius Base (definition, example)
substance that dissociates in water to produce OH-
ex: NaOH
Limitations of the Arrhenius Theory
- Rather than just ionizing, H+ ion attaches itself to water producing hydronium ion
- does not explain basic properties of ammonia (NH3) as it does not have OH ion
Bronsted-Lowry Acid
a substance from which a proton (H+) can be removed (DONATES H+)
Bronsted-Lowry Base
substance that can remove a proton from an acid (ACCEPTS/TAKES H+)
Any negative ion (anion) can be a bronsted-lowry base, not just OH-
Amphoteric Substance
can act as either an acid or a base
contains a H+ and an overall negative charge or lone pair
Strong Acids (characteristics, example)
100% ionization
[hydronium]=[initial acid]
single arrow, solve with stoichiometry
Ex: HCl, HBr, H2SO4
Weak Acids (characteristics, example)
only partially ionize
[hydronium]«[initial acid]
small Ka, equilibrium lies far left
double arrow, solve with ICE chart
Ex: anything with carbon, HF
Strong Bases (characteristics, example)
100% ionization, producing OH-
[OH-]=[initial base]
single arrow, solve with stoichiometry
Ex: metal + OH, NaOH, KOH, arrhenius bases (except beryllium)
Weak Bases (characteristics, example)
react with water to produce OH-
[OH-]«[initial base]
small Kb value, equilibrium lies far left
double arrow, solve with ICE chart
Ex: do not contain OH-, NH3, anything containing nitrogen
The smaller the Ka/Kb the ______ the acid/base and the ________ less it ionizes
Smaller the Ka/Kb the WEAKER the acid/base and the LESS it ionizes
What properties will the conjugate of a STRONG acid/base produce?
Negligible acid-base properties
What properties will the conjugate of a WEAK acid/base produce?
Weak acid-base properties
Polyprotic Acids
Acids that have more than one proton, can only transfer one proton at a time
[hydronium] = [OH-] produces a ______ solution
Neutral, pH=7
[hydronium] > [OH-] produces a ______ solution
Acidic, pH<7
[hydronium] < [OH-] produces a ______ solution
Basic, pH>7
Salt (definition, where cation and anion come from, what pH depends on)
An ionic compound containing a cation (+) and an anion (-)
Cation comes from the BASE
Anion comes from the ACID
pH depends on whether the ions are conjugates of strong or weak acids/bases
Salts that produce NEUTRAL Solutions (what type of acid and base)
Strong acid + Strong base = Neutral
Neither ion has acid/base properties
Salts that produce ACIDIC Solutions (what type of acid and base)
Strong acid + Weak base = Acidic
Cation (C.A. from weak base) acts as an acid, anion has no effect on pH
Salts that produce BASIC Solutions (what type of acid and base)
Weak acid + Strong base = Basic
Cation has no effect on pH, anion (C.B. of weak acid) acts as a base.
Titration (use)
used to determine the unknown concentration of an acid or a base
Equivalence Point [titration] Definition
point where acid and base are equal in moles
midpoint of steep rise on titration curve
How to know when End Point of Titration occurs
occurs when the indicator changes colour
Why is difference between equivalence and end point negligible? [titrations]**
Equivalence point is when the acid and base are equal in moles. You cannot see it/observe it during an experiment. End point is when you see the indicator change colour, as the pH rapidly changes at equivalence, we say the difference in pH between the end and equivalence point is negligible.
