reactivity 2.3

Question 1

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 (_____________)

Answer 1

evaporation

increase

condensation

Question 2

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?

Answer 2

equilibrium

only true in a closed system

Question 3

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?

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the reverse reaction (which initially has a 0 rate). why?
why does it start slowly and increases?

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when would this system reach equilibrium?

Answer 3

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!!!

Question 4

define equilibrium mixture

Answer 4

contents of the flask in an equilibrium reaction

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

they are being produced and destroyed at an equal rate

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

define equilibrium position

Answer 10

the proportion of reactant & product in the equilibrium mixture

Question 11

if an equilibrium lies to the RIGHT, define the reaction

Answer 11

it is a reaction where the mixture contains predominantly PRODUCTS

Question 12

if an equilibrium lies to the LEFT, define the reaction

Answer 12

it is a reaction where the mixture contains predominantly REACTANTS

Question 13

with the reaction:

aA + bB ⇌ cC + dD

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

Answer 13

K = [C]ᶜ × [D]ᵈ / [A]ᵃ × [B]ᵇ

Question 14

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

Answer 14

product / reactant

Question 15

with the reaction:

aA + bB ⇌ cC + dD

what are the forward AND reverse reactions?

Answer 15

forward: a + b → c + d

reverse: c + d → a + b

Question 16

what does ⇌ mean?

Answer 16

the reaction is reversible

Question 17

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

Answer 17

more products than reactants

⟹ equilibrium lies to the right

Question 18

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

Answer 18

more reactants than products

⟹ equilibrium lies to the left

Question 19

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?

Answer 19

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

Question 20

rules for writing equilibrium constant expressions x5

Answer 20

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

Question 21

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

Answer 21

0 to infinity
1 = equilibrium

Question 22

what is the extent of reaction K ≪ 1 ?

Answer 22

reaction hardly proceeds

Question 23

what is the extent of reaction K < 1 ?

Answer 23

equilibrium lies towards reactants

Question 24

what is the extent of reaction K = 1 ?

Answer 24

significant amounts of both R and P at equilibrium

Question 25

what is the extent of reaction K > 1 ?

Answer 25

equilibrium lies towards products

Question 26

what is the extent of reaction K ≫ 1 ?

Answer 26

reaction goes almost to completion

Question 27

K' is what?

Answer 27

the equilibrium constant of the reversed reaction

Question 28

K' equation

Answer 28

1/K

Question 29

define le chatelier's principle

Answer 29

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)

Question 30

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 ______)

Answer 30

forward reaction backward reaction reactant products right

Question 31

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 ______)

Answer 31

backward reaction product products right

Question 32

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

Answer 32

at equilibrium = concentration remains unchanged

Question 33

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

Answer 33

addition/removal of the P or R

Question 34

CO₂ + H₂ ⇋ H₂O (g) + CO a drying agent is added to absorb H₂O what shift is needed to turn towards equilibrium?

Answer 34

shift right (create ↑ product)

Question 35

H₂ (g) + I₂ (g) ⇋ 2HI (g) some nitrogen gas is added what shift is needed to turn towards equilibrium?

Answer 35

doesn't affect reaction (no change)

Question 36

NaCl (s) + H₂SO₄ (l) ⇋ Na₂SO₄ (s) + HCl (g) reaction is carried out in an open container what shift is needed to turn towards equilibrium?

Answer 36

shift right (create ↑ product)

Question 37

AgCl (s) ⇋ Ag⁺ (aq) + Cl⁻ (aq) some NaCl is added to the solution what shift is needed to turn towards equilibrium?

Answer 37

shift left

Question 38

H₂O (l) ⇋ H₂O (g) water evaporates from an open container what shift is needed to turn towards equilibrium?

Answer 38

shift right

Question 39

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

Answer 39

number of molecules

Question 40

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

Answer 40

fewer

Question 41

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

Answer 41

higher

Question 42

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

Answer 42

remains the same

Question 43

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 ________

Answer 43

pressure ↑ ⟹ equilibrium shifts RIGHT & creates more CH₃OH pressure ↓ ⟹ equilibrium shifts LEFT & creates more CO and H₂

Question 44

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?

Answer 44

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

Question 45

is K temperature dependant?

Answer 45

yes

Question 46

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

Answer 46

releases product

Question 47

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

Answer 47

absorbs reactant

Question 48

2NO₂ (g) ⇌ N₂O₄ (g) ΔH = -57kJ mol⁻¹ exo or endo thermic?

Answer 48

exo ⟹ E or heat is a product 2NO₂ (g) ⇌ N₂O₄ (g) + heat

Question 49

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 ________

Answer 49

producing forward exothermic right product N₂O₄ increases

Question 50

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 ________

Answer 50

reducing backward endothermic left reactant NO₂ decreases

Question 51

N₂ (g) + O₂ (g) ⇋ 2NO (g) ΔH = +181kJ mol⁻¹ exo or endo thermic?

Answer 51

endo ⟹ heat is a reactant N₂ (g) + O₂ (g) + heat ⇋ 2NO (g)

Question 52

N₂ (g) + O₂ (g) ⇋ 2NO (g) ΔH = +181kJ mol⁻¹ temperature ↓ ⟹ equilibrium shifts ______ ⟹ K will _______ temperature ↑ ⟹ equilibrium shifts ______ ⟹ K will _______

Answer 52

temperature ↓ ⟹ equilibrium shifts LEFT (more reactants) ⟹ K will DECREASE temperature ↑ ⟹ equilibrium shifts RIGHT (more products) ⟹ K will INCREASE

Question 53

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

Answer 53

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

Question 54

does the effect of: concentration change in position of equilibrium? change in value of K?

Answer 54

changes position of equilibrium does not change value of K

Question 55

does the effect of: pressure change in position of equilibrium? change in value of K?

Answer 55

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

Question 56

does the effect of: temperature change in position of equilibrium? change in value of K?

Answer 56

changes position of equilibrium changes value of K

Question 57

does the effect of: a catalyst change in position of equilibrium? change in value of K?

Answer 57

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

Question 58

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

Answer 58

N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g) ΔH = -93kJ mol⁻¹

Question 59

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

Answer 59

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)