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reactivity 2.3 Flashcards

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1
Q

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 (_____________)

A

evaporation

increase

condensation

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2
Q

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?

A

equilibrium

only true in a closed system

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3
Q

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?

A

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!!!

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4
Q

define equilibrium mixture

A

contents of the flask in an equilibrium reaction

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5
Q

characteristics of a physical and a chemical system at equilibrium: equilibrium is dynamic

A

the reaction has not stopped, but both forward and backward reactions are still occurring at the same rate

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6
Q

characteristics of a physical and a chemical system at equilibrium: equilibrium is achieved in a closed system

A

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

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7
Q

characteristics of a physical and a chemical system at equilibrium: the concentrations of reactants and products remain constant at equilibrium

A

they are being produced and destroyed at an equal rate

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8
Q

characteristics of a physical and a chemical system at equilibrium: at equilibrium there is no change in macroscopic properties

A

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

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9
Q

characteristics of a physical and a chemical system at equilibrium: equilibrium can be reached from either direction

A

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

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10
Q

define equilibrium position

A

the proportion of reactant & product in the equilibrium mixture

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11
Q

if an equilibrium lies to the RIGHT, define the reaction

A

it is a reaction where the mixture contains predominantly PRODUCTS

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12
Q

if an equilibrium lies to the LEFT, define the reaction

A

it is a reaction where the mixture contains predominantly REACTANTS

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13
Q

with the reaction:

aA + bB ⇌ cC + dD

what is the equilibrium constant expression (of the forward reaction)?

A

K = [C]ᶜ × [D]ᵈ / [A]ᵃ × [B]ᵇ

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14
Q

with the equilibrium constant expression, are reactants or products on top?

A

product / reactant

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15
Q

with the reaction:

aA + bB ⇌ cC + dD

what are the forward AND reverse reactions?

A

forward: a + b → c + d

reverse: c + d → a + b

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16
Q

what does ⇌ mean?

A

the reaction is reversible

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17
Q

higher K ⟹ at equilibrium, there are proportionately more ________ than _________ ⟹ equilibrium lies to the ________

A

more products than reactants

⟹ equilibrium lies to the right

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18
Q

lower K ⟹ at equilibrium, there are proportionately more ________ than _________ ⟹ equilibrium lies to the ________

A

more reactants than products

⟹ equilibrium lies to the left

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19
Q

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?

A

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

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20
Q

rules for writing equilibrium constant expressions x5

A

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

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21
Q

what is the range of K values? what # is equilibrium?

A

0 to infinity
1 = equilibrium

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22
Q

what is the extent of reaction K ≪ 1 ?

A

reaction hardly proceeds

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23
Q

what is the extent of reaction K < 1 ?

A

equilibrium lies towards reactants

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24
Q

what is the extent of reaction K = 1 ?

A

significant amounts of both R and P at equilibrium

25
Q

what is the extent of reaction K > 1 ?

A

equilibrium lies towards products

26
Q

what is the extent of reaction K ≫ 1 ?

A

reaction goes almost to completion

27
Q

K’ is what?

A

the equilibrium constant of the reversed reaction

28
Q

K’ equation

A

1/K

29
Q

define le chatelier’s principle

A

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)

30
Q

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 ______)

A

forward reaction

backward reaction

reactant

products

right

31
Q

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 ______)

A

backward reaction

product

products

right

32
Q

in a graph showing concentrations over time, what do parallel lines mean?

A

at equilibrium = concentration remains unchanged

33
Q

in a graph showing concentrations over time, what do sudden jumps up/down in a concentration of P or R mean?

A

addition/removal of the P or R

34
Q

CO₂ + H₂ ⇋ H₂O (g) + CO

a drying agent is added to absorb H₂O

what shift is needed to turn towards equilibrium?

A

shift right (create ↑ product)

35
Q

H₂ (g) + I₂ (g) ⇋ 2HI (g)

some nitrogen gas is added

what shift is needed to turn towards equilibrium?

A

doesn’t affect reaction (no change)

36
Q

NaCl (s) + H₂SO₄ (l) ⇋ Na₂SO₄ (s) + HCl (g)

reaction is carried out in an open container

what shift is needed to turn towards equilibrium?

A

shift right (create ↑ product)

37
Q

AgCl (s) ⇋ Ag⁺ (aq) + Cl⁻ (aq)

some NaCl is added to the solution

what shift is needed to turn towards equilibrium?

A

shift left

38
Q

H₂O (l) ⇋ H₂O (g)

water evaporates from an open container

what shift is needed to turn towards equilibrium?

A

shift right

39
Q

equilibria involving gases will be affected by a change in pressure if the reaction involves a change in the ________________________

A

number of molecules

40
Q

increase in pressure ⟹ system responds to decrease this pressure by favouring the side with the _______ number of molecules

A

fewer

41
Q

decrease in pressure ⟹ system responds to increase this pressure by favouring the side with the _______ number of molecules

A

higher

42
Q

value of K will be unchanged as long as the temperature what?

A

remains the same

43
Q

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 ________

A

pressure ↑ ⟹ equilibrium shifts RIGHT & creates more CH₃OH

pressure ↓ ⟹ equilibrium shifts LEFT & creates more CO and H₂

44
Q

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?

A

it will have NO effect because there are identical #s of gaseous molecules

45
Q

is K temperature dependant?

A

yes

46
Q

exothermic reactions (ΔH < 0) ⟹ _______ energy ⟹ energy is a _______

A

releases

product

47
Q

endothermic reactions (ΔH > 0) ⟹ _______ energy ⟹ energy is a _______

A

absorbs

reactant

48
Q

2NO₂ (g) ⇌ N₂O₄ (g)

ΔH = -57kJ mol⁻¹

exo or endo thermic?

A

exo ⟹ E or heat is a product

2NO₂ (g) ⇌ N₂O₄ (g) + heat

49
Q

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 ________

A

producing

forward exothermic

right

product

N₂O₄

increases

50
Q

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 ________

A

reducing

backward endothermic

left

reactant

NO₂

decreases

51
Q

N₂ (g) + O₂ (g) ⇋ 2NO (g)

ΔH = +181kJ mol⁻¹

exo or endo thermic?

A

endo ⟹ heat is a reactant

N₂ (g) + O₂ (g) + heat ⇋ 2NO (g)

52
Q

N₂ (g) + O₂ (g) ⇋ 2NO (g)

ΔH = +181kJ mol⁻¹

temperature ↓ ⟹ equilibrium shifts ______ ⟹ K will _______

temperature ↑ ⟹ equilibrium shifts ______ ⟹ K will _______

A

temperature ↓ ⟹ equilibrium shifts LEFT (more reactants) ⟹ K will DECREASE

temperature ↑ ⟹ equilibrium shifts RIGHT (more products) ⟹ K will INCREASE

53
Q

will a catalyst have an effect on equilibrium position or value of K? why or why not?

A

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

54
Q

does the effect of:
concentration

change in position of equilibrium?
change in value of K?

A

changes position of equilibrium
does not change value of K

55
Q

does the effect of:
pressure

change in position of equilibrium?
change in value of K?

A

changes position of equilibrium if reaction involves a change in the number of gas molecules
does not change value of K

56
Q

does the effect of:
temperature

change in position of equilibrium?
change in value of K?

A

changes position of equilibrium
changes value of K

57
Q

does the effect of:
a catalyst

change in position of equilibrium?
change in value of K?

A

does not change position of equilibrium
does not change value of K

58
Q

what reaction is the haber process is based on the reactions? (equation and enthalpy change)

A

N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g)

ΔH = -93kJ mol⁻¹

59
Q

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

A

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)

chemistry (8 decks)

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