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Chemistry AH > Chemical Equillibrium > Flashcards

Chemical Equillibrium Flashcards

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1
Q

When is a chemical reaction in equilibrium?

A

When the position of the reactants and products remains constant indefinitely.

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2
Q

What does the equilibrium constant K do?

A

Characterises the equilibrium composition of the reaction mixture.

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3
Q

What is the general reaction, aA+bB -> cC+dD, equilibrium expression?

A

K = [C]^c [D]^d / [A]^a [B]^b

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4
Q

what are
1.[A] [B] [C] [D]
2.a b c d

A
  1. Equilibrium concentrations of A B C D
  2. The stoichiometric coefficients in the balanced reaction equation
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5
Q

What does the equilibrium indicate?

A

the position of equilibrium

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6
Q

What value of concentrations are pure liquids and pure solids given in the equilibrium expression

A

taken as constant = 1

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7
Q

What is the (numerical value of) equilibrium constant dependant on?

A

reaction temperature

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8
Q

What is the (numerical value of) equilibrium constant independant of?

A

concentration and/or pressure

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9
Q

For endothermic reactions, what happens to the K value and yield of products if the temperature is increased?

A

increase in K
increase in yield of product

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10
Q

For exothermic reactions, what happens to the K value and yield of products if the temperature is increased?

A

decrease in K
decrease in yield of product

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11
Q

What does le Chatellier’s principle state?

A

If any changes are applied to a reaction at equilibrium, the position of equilibrium will shift to try and minimise the change

(an system at equilibrium will counteract an applied change)

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12
Q

Where can an equilibrium be established

A

only in a closed system

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13
Q

What does a high K mean? (above 1)

A

higher percent of products in equilibrium mixture

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14
Q

What does a low K mean? (below 1)

A

lower percentage of products in equilibrium mixture

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15
Q

What is homogeneous equilibrium?

A

when all species are in the same state

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16
Q

What is heterogeneous equilibrium?

A

It has species that are in more than one state

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17
Q

What happens when concentration is changed in an equilibrium and why?

A

The value of K remains constant (at the same temp) as the equilibrium position shifts which results in changes in the concentrations of the species in the reaction

18
Q

Effect of a catalyst on an equilibrium?

A

-lowers activation energy for both forwards and reverse reactions by the same amount
-no change in the equilibrium concentration so position of equilibrium remains unchanged
-catalysts speed up the rate at which equilibrium is established

19
Q

What does K NOT indicate?

A

the rate at which dynamic equilibrium is established

20
Q

In water and aqueous solutions, what is there an equilibrium between?

A

the water molecules + hydronium (hydrogen) and hydroxide ions

21
Q

Ionisation of water formula

A

H2O (l) + H2O (l) <> H3O+ (aq) + OH- (aq)

H2O = acid
H2O = base
H3O+ = conjugate acid
OH- = conjugate base

22
Q

what does H3O+ represent?

A

a hydronium ion/hydrated proton
( H+ in shorthand)

23
Q

What is one word to describe water and what does it mean?

A

amphoteric-can react as an acid and a base

24
Q

What is the dissociation constant for the ionisation of water known as? (+what is it represented by+formula)

A

the ionic product and is represent by Kw

Kw=[H3O+][OH-]

25
Q

What does the value of the ionic product vary with?

A

tmeperature

26
Q

What is the value of Kw at 25degreesC?

A

1x10^-14

27
Q

What is the Brønsted-Lowry definition of a base and an acid

A

Base-proton acceptor
Acid-proton donator

28
Q

What is there for every acid??

A

a conjugate base, formed by the loss (donation) of a proton

(loses H)

29
Q

What is there for every base?

A

a conjugate acid, formed by the gain (accept) of a proton

(gains H)

30
Q

What makes acids and bases strong?

A

they are completely dissociated into ions in aqueous solution

–>

Equilibrium lies (almost) completely to the right (lots of products)

100% of H+ or OH- ions to react at all times

31
Q

What makes acids and bases weak?

A

they are only partially dissociated into ions in aqueous solution

<—>

Equilibrium lies (almost) completely to the right (lots of products)

Only a small proportion of H+ or OH- ions available

-ions react with another chemical and are removed from the equilibrium
-concentration of product is reduced
-equilibrium shifts to the right to replace ions
-more molecules dissociate to replace removed ions
-molecules will continue to dissociate to replace H+ ions as they continue to be removed by reacting

32
Q

examples of strong acids

A

hydrochloric acid HCl
sulfuric acid H2SO4
nitric acid HNO3

33
Q

examples of weak acids

A

ethanoic acid (carboxylic acids)
carbonic acid H2CO3
sulfurous acid H2SO3

34
Q

example of a strong base

A

group 1 and 2 metal hydroxides
(except Mg)

35
Q

examples of weak bases

A

ammonia and amines

36
Q

How can the weakly nature of solutions of carboxylic acids, sulfur dioxide, and carbon dioxide be explained?

A

by reference to equations showing the equilibria

37
Q

How can the weakly alkaline nature of a solution of ammonia or amines be explained?

A

by reference to an equation showing the equilibrium

38
Q

Me formula for pure water

A

Kw=[H+][OH-]

39
Q

What can Kw, the ionic product, be used to calculate?

A

pH values for strong acids and strong bases (since they dissociate fully into ions)

40
Q

what is the pH?

A

potential of hydrogen ions

41
Q

difference between monoprotic and diprotic?

what volume and concentration of HCl has the same neutralising ability as 50cm^3 of 1mol/l of H2SO4?

A

monoprotic
HCl and CH3COOH
1 H+ ion is released per molecule

diprotic
sulphuric acid
2 H+ ions released per molecule

100cm^3 of 1mol/l

Chemistry AH (7 decks)

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