reactivity 2.3 Flashcards
at room temperature, a significant number of Br₂ will have enough E to escape from the liquid state and form vapour (____________)
in a sealed container (a closed system), the Br₂ (g) cannot escape ⟹ _________ in Br₂ (g) concentration ⟹ some vapour molecules will collide with the surface of the liquid and loses E (_____________)
evaporation
increase
condensation
when rate of evaporation = rate of condensation ⟹ no net change in amounts of liquid and gas present ⟹ a system at ____________
in what type(s) of system(s) is this true?
equilibrium
only true in a closed system
2HI (g) ⇌ H₂ (g) + I₂ (g)
2HI and H₂ are colourless gases
I₂ is a purple gas
at the start of the reaction there is no purple colour
as reaction continues, increase in the purple color is observed [ due to ↑ I₂ (g) ]
would the purple colour continue to increase? why or why not?
-
the reverse reaction (which initially has a 0 rate). why?
why does it start slowly and increases?
-
when would this system reach equilibrium?
no
the rate of dissociation of HI is fastest at the start when [HI] is greatest, and falls as the reaction proceeds
-
there is no H₂ / I₂
as [H₂] and [I₂] increases
-
when the rate of dissociation of HI = the rate of the reverse reaction of association between H₂ and I₂ (so concentrations remain constant)
see lesson 01 page 3 for reaction graphs!!!
define equilibrium mixture
contents of the flask in an equilibrium reaction
characteristics of a physical and a chemical system at equilibrium: equilibrium is dynamic
the reaction has not stopped, but both forward and backward reactions are still occurring at the same rate
characteristics of a physical and a chemical system at equilibrium: equilibrium is achieved in a closed system
a closed system has no exchange of matter with the surroundings so equilibrium is achieved where both reactants and products can react and recombine with each other
characteristics of a physical and a chemical system at equilibrium: the concentrations of reactants and products remain constant at equilibrium
they are being produced and destroyed at an equal rate
characteristics of a physical and a chemical system at equilibrium: at equilibrium there is no change in macroscopic properties
macroscopic properties are observable properties such as colour and density
these do not change as they depend on the concentrations of the components of the mixture
characteristics of a physical and a chemical system at equilibrium: equilibrium can be reached from either direction
the same equilibrium mixture will result under the same conditions, no matter whether the reaction is started with all reactants, all products, or a mixture of both
define equilibrium position
the proportion of reactant & product in the equilibrium mixture
if an equilibrium lies to the RIGHT, define the reaction
it is a reaction where the mixture contains predominantly PRODUCTS
if an equilibrium lies to the LEFT, define the reaction
it is a reaction where the mixture contains predominantly REACTANTS
with the reaction:
aA + bB ⇌ cC + dD
what is the equilibrium constant expression (of the forward reaction)?
K = [C]ᶜ × [D]ᵈ / [A]ᵃ × [B]ᵇ
with the equilibrium constant expression, are reactants or products on top?
product / reactant
with the reaction:
aA + bB ⇌ cC + dD
what are the forward AND reverse reactions?
forward: a + b → c + d
reverse: c + d → a + b
what does ⇌ mean?
the reaction is reversible
higher K ⟹ at equilibrium, there are proportionately more ________ than _________ ⟹ equilibrium lies to the ________
more products than reactants
⟹ equilibrium lies to the right
lower K ⟹ at equilibrium, there are proportionately more ________ than _________ ⟹ equilibrium lies to the ________
more reactants than products
⟹ equilibrium lies to the left
consider the following reactions (K value at 550K)
H₂ (g) + I₂ (g) ⇌ 2HI (g) (K value = 2)
H₂ (g) + Br₂ (g) ⇌ 2HBr (g) (K value = 10¹⁰)
H₂ (g) + Cl₂ (g) ⇌ 2HCl (g) (K value = 10¹⁸)
which reacted the least? which reacted the most?
H₂ (g) + I₂ (g) ⇌ 2HI (g) (K value = 2) ⟹ reacted the least ⟹ least product
H₂ (g) + Cl₂ (g) ⇌ 2HCl (g) (K value = 10¹⁸) ⟹ reacted the most ⟹ most product
rules for writing equilibrium constant expressions x5
coefficients = exponents
products/reactants
state (g/l/aq/s)
use [ ]ˣ around each product or reactant
multiply products with products OR reactants with reactants if there are multiple ones
what is the range of K values? what # is equilibrium?
0 to infinity
1 = equilibrium
what is the extent of reaction K ≪ 1 ?
reaction hardly proceeds
what is the extent of reaction K < 1 ?
equilibrium lies towards reactants
what is the extent of reaction K = 1 ?
significant amounts of both R and P at equilibrium
what is the extent of reaction K > 1 ?
equilibrium lies towards products
what is the extent of reaction K ≫ 1 ?
reaction goes almost to completion
K’ is what?
the equilibrium constant of the reversed reaction
K’ equation
1/K
define le chatelier’s principle
a system at equilibrium when subjected to a change will respond in such a way as to minimize the effect of the change
(whatever we do to a system at equilibrium, the system will respond in the opposite way)
if the concentration of one of the reactants increases ⟹ rate of _____________ increases while the _____________ will not be affected ⟹ reaction rates will no longer be equal ⟹ system responds by removing ____________ ⟹ equilibrium shifts in favour of __________ (to the ______)
forward reaction
backward reaction
reactant
products
right
if the concentration of product decreases by removing product from the equilibrium mixture ⟹ rate of __________________ decreases ⟹ equilibrium is disrupted ⟹ system responds by making more _________ ⟹ equilibrium shifts in favour of _________ (to the ______)
backward reaction
product
products
right
in a graph showing concentrations over time, what do parallel lines mean?
at equilibrium = concentration remains unchanged
in a graph showing concentrations over time, what do sudden jumps up/down in a concentration of P or R mean?
addition/removal of the P or R
CO₂ + H₂ ⇋ H₂O (g) + CO
a drying agent is added to absorb H₂O
what shift is needed to turn towards equilibrium?
shift right (create ↑ product)
H₂ (g) + I₂ (g) ⇋ 2HI (g)
some nitrogen gas is added
what shift is needed to turn towards equilibrium?
doesn’t affect reaction (no change)
NaCl (s) + H₂SO₄ (l) ⇋ Na₂SO₄ (s) + HCl (g)
reaction is carried out in an open container
what shift is needed to turn towards equilibrium?
shift right (create ↑ product)
AgCl (s) ⇋ Ag⁺ (aq) + Cl⁻ (aq)
some NaCl is added to the solution
what shift is needed to turn towards equilibrium?
shift left
H₂O (l) ⇋ H₂O (g)
water evaporates from an open container
what shift is needed to turn towards equilibrium?
shift right
equilibria involving gases will be affected by a change in pressure if the reaction involves a change in the ________________________
number of molecules
increase in pressure ⟹ system responds to decrease this pressure by favouring the side with the _______ number of molecules
fewer
decrease in pressure ⟹ system responds to increase this pressure by favouring the side with the _______ number of molecules
higher
value of K will be unchanged as long as the temperature what?
remains the same
CO (g) + 2H₂ (g) ⇋ CH₃OH (g)
(3 mole of (g)) ⇋ (1 mole of (g))
(all gases)
pressure ↑ ⟹ equilibrium shifts ______ & creates more ________
pressure ↓ ⟹ equilibrium shifts ______ & creates more ________
pressure ↑ ⟹ equilibrium shifts RIGHT & creates more CH₃OH
pressure ↓ ⟹ equilibrium shifts LEFT & creates more CO and H₂
H₂ (g) + I₂ (g) ⇋ 2HI (g)
(2 mole of (g)) ⇋ (2 mole of (g))
(all gases)
how will a change in pressure affect position of equilibrium?
it will have NO effect because there are identical #s of gaseous molecules
is K temperature dependant?
yes
exothermic reactions (ΔH < 0) ⟹ _______ energy ⟹ energy is a _______
releases
product
endothermic reactions (ΔH > 0) ⟹ _______ energy ⟹ energy is a _______
absorbs
reactant
2NO₂ (g) ⇌ N₂O₄ (g)
ΔH = -57kJ mol⁻¹
exo or endo thermic?
exo ⟹ E or heat is a product
2NO₂ (g) ⇌ N₂O₄ (g) + heat
2NO₂ (g) ⇌ N₂O₄ (g)
ΔH = -57kJ mol⁻¹
temperature decreases ⟹ system responds by ________ heat ⟹ favouring the ______ ______ reaction ⟹ equilibrium will shift to the ________ (in favour of the ______) ⟹ more _______ will be produced ⟹ K ________
producing
forward exothermic
right
product
N₂O₄
increases
2NO₂ (g) ⇌ N₂O₄ (g)
ΔH = -57kJ mol⁻¹
temperature increases ⟹ system responds by ________ heat ⟹ favouring the ______ ______ reaction ⟹ equilibrium will shift to the ________ (in favour of the ______) ⟹ more _______ will be produced ⟹ K ________
reducing
backward endothermic
left
reactant
NO₂
decreases
N₂ (g) + O₂ (g) ⇋ 2NO (g)
ΔH = +181kJ mol⁻¹
exo or endo thermic?
endo ⟹ heat is a reactant
N₂ (g) + O₂ (g) + heat ⇋ 2NO (g)
N₂ (g) + O₂ (g) ⇋ 2NO (g)
ΔH = +181kJ mol⁻¹
temperature ↓ ⟹ equilibrium shifts ______ ⟹ K will _______
temperature ↑ ⟹ equilibrium shifts ______ ⟹ K will _______
temperature ↓ ⟹ equilibrium shifts LEFT (more reactants) ⟹ K will DECREASE
temperature ↑ ⟹ equilibrium shifts RIGHT (more products) ⟹ K will INCREASE
will a catalyst have an effect on equilibrium position or value of K? why or why not?
no, all a catalyst does is provide an alternate route for the reaction with a lower Eₐ
as the forward and backward reactions pass through the same transition state, a catalyst thus lowers the Eₐ for both forward and backward reactions
does the effect of:
concentration
change in position of equilibrium?
change in value of K?
changes position of equilibrium
does not change value of K
does the effect of:
pressure
change in position of equilibrium?
change in value of K?
changes position of equilibrium if reaction involves a change in the number of gas molecules
does not change value of K
does the effect of:
temperature
change in position of equilibrium?
change in value of K?
changes position of equilibrium
changes value of K
does the effect of:
a catalyst
change in position of equilibrium?
change in value of K?
does not change position of equilibrium
does not change value of K
what reaction is the haber process is based on the reactions? (equation and enthalpy change)
N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g)
ΔH = -93kJ mol⁻¹
N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g)
(4 mole of (g)) ⇋ (2 mole of (g)) (all gasses)
ΔH = -93kJ mol⁻¹
deduce the conditions that would maximize the conversion of reactants to products (shifts right) in this reaction
for the equilibrium to shift to the right, the scale must look like a heavier left size ⟹ removing products/adding reactants
(removing NH₃ (g) or add N₂ (g) or add H₂ (g))
(remove heat/decrease temperature or increase pressure)
