ATAR Unit 3 (1) Flashcards
open system
exchanges energy & matter w. surroundings
closed system
exchanges only energy w. surroundings
reversible reaction
reaction where the products once formed can react together to re-form the reactants
reversibility [chemical]
only some chemical changes are reversible
reversibility [physical]
physical changes are usually reversible
four common reversible systems
evaporation & condensation of water [physical]
saturated sugar / salt solution [physical]
oxygen transport in blood [physical]
synthesis of ammonia [chemical]
static equilibrium
position of balance is achieved but no processes are happening [e.g. seesaw]
dynamic equilibrium
equal rate of forward & reverse reactions is achieved in closed systems
macroscopic properties remain constant & microscopic processes continue
reversibility [considering activation energy]
reactants collide w. sufficient energy [Eₐ] to form products
products collide w. sufficient energy [reverse Eₐ] to form reactants
extent of reaction
indicates how much product is formed at equilibrium
rate of reaction
measures the change in reactants & products w. time
graphing rate vs time
shape of the graph [rate theory]
graphing concentration vs time
stoichiometry of the reaction [coefficient]
le chatalier’s principle
if stress is applied to a system at equilibrium, the system will act to oppose the stress & restore equilibrium
increase temperature [exothermic reaction]
endothermic reaction absorbs heat
reverse reaction is favoured
moves to left-hand-side
reactants are favoured
K𝒸 decreases
decrease temperature [exothermic reaction]
exothermic reaction releases heat
forward reaction is favoured
moves to right-hand-side
products are favoured
K𝒸 increases
increase temperature [endothermic reaction]
endothermic reaction absorbs heat
forward reaction is favoured
moves to right-hand-side
products are favoured
K𝒸 increases
decrease temperature [endothermic reaction]
exothermic reaction releases heat
reverse reaction is favoured
moves to left-hand-side
reactants are favoured
K𝒸 decreases
increasing temperature effect [collision theory]
more kinetic energy within reactants & products
molecules move faster
more successful collisions
greater rate of reaction
pressure’s effect on K𝒸
changing pressure has no effect on the K𝒸 value
what if the number of molecules is equal on both sides of the chemical equation [2 : 2 molecules equation] ? [pressure]
change in pressure will not shift the position of equilibrium [no effect]
volume’s effect on pressure
if volume is doubled, pressure is halved
if volume is halved, pressure is doubled
increase pressure [3 : 2 molecules equation]
moves to the side of fewest molecules
net forward reaction
decrease pressure [3 : 2 molecules equation]
moves to the side of more molecules
net reverse reaction
increasing pressure effect [collision theory]
reduced volume equals increased pressure
molecules are closer together
increased frequency of collisions
greater rate of reaction
increase reactant
formation of more products
position of equilibrium shifts right
net forward reaction
increase product
formation of more reactants
position of equilibrium shifts left
net reverse reaction
decrease reactant
formation of more reactants
position of equilibrium shifts left
net reverse reaction
decrease product
formation of more products
position of equilibrium shifts right
net forward reaction
inert gas’ effect on K𝒸
adding an inert gas has no effect on the K𝒸 value
concentration’s effect on K𝒸
changing concentration has no effect on the K𝒸 value
increase dilution
moves to the side of more molecules
equilibrium is restored
catalyst’s effect on K𝒸
a catalyst has no effect on the K𝒸 value
homogenous system
reactants & products are in the same phase
heterogeneous system
reactants & products are in different phases
K𝒸 expression
products to the power of their coefficient[s] divided by reactants to the power of their coefficient[s]
what species do & do not appear in a K𝒸 expression ?
solids & liquids do not appear
aqueous & gases do appear
liquids do appear [if all species in the reaction are liquid]
liquids do appear [if H₂O is a reactant / product]
Q𝒸 > K𝒸
moves to left-hand-side
more reactants
Q𝒸 < K𝒸
moves to right-hand-side
more products
10⁻⁴ < K𝒸 < 10⁴
extent of reaction is significant
reactants = products [at equilibrium]
K𝒸 > 10⁴
extent of reaction is complete
products > reactants [at equilibrium]
equilibrium lies to the right-hand-side
K𝒸 < 10⁻⁴
extent of reaction is negligible
reactants > products [at equilibrium]
equilibrium lies to the left-hand-side
reversed equation’s effect on K𝒸
K𝒸 is inversed
doubled equation’s effect on K𝒸
K𝒸 is squared
halved equation’s effect on K𝒸
K𝒸 is square-rooted
acid [arrhenius model]
substance that produces hydrogen ions [H⁺] in an aqueous solution [e.g. HCl]
base [arrhenius model]
substance that produces hydroxide ions [OH⁻] in an aqueous solution [e.g. NaOH]
neutralization reaction [arrhenius model]
reaction where hydrogen ions react w. hydroxide ions to form water [e.g. H₂O ⇌ H⁺ + OH⁻]
acid + base →
salt + water [e.g. HCl + NaOH → NaCl + H₂O]
acid + metal →
salt + hydrogen gas [e.g. 2HCl + Mg → MgCl₂ + H₂]
acid + carbonate →
salt + water + carbon dioxide gas [e.g. HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
acid [brønsted–lowry model]
proton [H⁺] donor [e.g. HSO₄⁻]
base [brønsted–lowry model]
proton [H⁺] acceptor [e.g. NH₃]
neutralization reaction [brønsted–lowry model]
reaction where an acid reacts w. a base [e.g. NH₃ + H₂O ⇌ NH₄⁺ + OH⁻]
conjugate acid-base pair
two species that differ by one proton [H⁺] [e.g. HNO₃ & NO₃⁻]
conjugate acid
when a base accepts a proton [H⁺]
conjugate base
when an acid donates a proton [H⁺]
amphiprotic substances
can act as either acids or bases; can either donate or accept protons [e.g. H₂O]
monoprotic acid
can donate one proton [e.g. HCl]
diprotic acid
can donate two protons [e.g. H₂SO₄]
triprotic acid
can donate three protons [e.g. H₃PO₄]
polyprotic acid
can donate more than one proton to a base
extent of dissociation [polyprotic acids]
first dissociation is greater than each subsequent dissociation; final dissociation occurs to the least extent; subsequent acids become progressively weaker
strong acid
dissociates completely in aqueous solution; readily donates protons [e.g. HCl, H₂SO₄, HNO₃]
weak acid
dissociates partially in aqueous solution; high proportion of undissociated acid particles [e.g. CH₃COOH, H₂CO₃, H₃PO₄]
strong base
dissociates completely in solution; readily accepts protons [e.g. NaOH]
weak base
dissociates partially in solution; high proportion of undissociated base particles [e.g. NH₃]
relative strength relationship of conjugate acid-base pairs
stronger the acid, weaker the conjugate base [if an acid readily donates a proton, its conjugate base does not readily accept it back]
stronger the base, weaker the conjugate acid [if a base readily accepts a proton, its conjugate acid does not readily donate it forward]
strength vs concentration
strength [strong / weak] refers to the degree of dissociation [tendency to donate / accept protons] of an acid / base
concentration [concentrated / dilute] refers to the relative amount of solute in a given volume of solution
water
very weak electrolyte & undergoes self-ionization to a very small extent
K𝒸 define
equilibrium constant / point of balance that exists in a reaction
Kᴡ define
ionic product / ionization constant of water
Kᴡ expression
[H₃O⁺][OH⁻] = 1 x 10⁻¹⁴
temperature’s effect on Kᴡ
increase temperature, increase Kᴡ
decrease temperature, decrease Kᴡ
pH expression
-log[H₃O⁺]
dilution’s effect on pH [strong acids & bases]
no effect on the number of moles [c₁V₁ = c₂V₂]
dilution’s effect on pH [acid at 25ºC]
pH increases until close to 7
dilution’s effect on pH [base at 25ºC]
pH decreases until close to 7
buffer
solution that is conjugate in nature & resists changes in pH when small amounts of acid / bases are added
general equation [buffer]
HA ⇌ H⁺ + A⁻
BOH ⇌ B⁺ + OH⁻
buffer composition
weak acid & conjugate base
weak base & conjugate acid
increase H⁺ to buffer [small amount]
H⁺ reacts w. A⁻
moves to left-hand-side [le chatalier’s principle]
more HA
[H⁺] remains relatively constant
pH does not change significantly
increase H⁺ to buffer [large amount]
H⁺ reacts w. A⁻
moves to left-hand-side [le chatalier’s principle]
more HA
exhaustion of A⁻
[H⁺] soars
pH plummets
increase OH⁻ to buffer [small amount]
OH⁻ reacts w. H⁺ [neutralization]
moves to right-hand-side [le chatalier’s principle]
more weak acid HA dissociates
[H⁺] remains relatively constant
pH does not change significantly
increase OH⁻ to buffer [large amount]
OH⁻ reacts w. H⁺ [neutralization]
moves to right-hand-side [le chatalier’s principle]
more weak acid HA dissociates
exhaustion of HA
[H⁺] plummets
pH soars
two solutions [buffer]
CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ [inverse response]
Kₐ define
acid dissociation constant
larger Kₐ
greater extent of dissociation
more products
more [H⁺]
stronger the acid
smaller Kₐ
lesser extent of dissociation
more reactants
less [H⁺]
weaker the acid
Kₐ of polyprotic acids
first dissociation has a greater Kₐ than each subsequent dissociation; each following step, Kₐ decreases; it becomes increasingly harder to lose a proton as the acid species becomes increasingly negative
acid-base indicator
weak acid / weak base where the conjugate acid form is one colour & the conjugate base form is another colour
pH range [indicator]
related to the indicator’s dissociation constant
position of equilibrium changes depending on the solution’s pH
colour change occurs when pKₐ = pH
equivalence point [neutralization reaction]
when the amount [number of moles] of acid & base are in stoichiometric ratio [equal]
end point
when the indicator changes colour
corresponds closely w. the equivalence point
transition point [indicator]
when concentration of the acid form & base form are equal
pH = pKₐ = -log[H⁺]
equivalence point
when the amount [number of moles] between reactants are in stoichiometric ratio [equal]
half equivalence point
when the amount [number of moles] between conjugate acid-base pair are in stoichiometric ratio [equal]
pH = pKₐ = -log[H⁺]
useful relationships [pKᴡ]
pKᴡ = pH + pOH = 14
pKᴡ = pKₐ + pKᵦ = 14
useful relationships [Kᴡ]
Kᴡ = [H₃O⁺][OH⁻] = 1 x 10⁻¹⁴
Kᴡ = Kₐ x Kᵦ = 1 x 10⁻¹⁴
