7: Equilibria

Question 1

Brønsted-Lowry acid [2]

Answer 1

​-Proton donors.
- These species release hydrogen ions in solution

Question 2

Brønsted-Lowry base

Answer 2

​Proton acceptors

Question 3

Catalysts [3]

Answer 3

-Increases the rate of reaction
-by providing an alternative reaction route with a lower
activation energy.
-A catalyst does not affect the equilibrium constant since it increases the rate of the forward and backward reaction equally.

Question 4

CH​3​COOH

Answer 4

The molecular formula for ethanoic acid.

Question 5

Closed system [2]

Answer 5

​-A system where there is ​only heat exchange occurring between the system and its surroundings.
-No matter can enter or exit the system.

Question 6

Dynamic equilibrium [2]

Answer 6

-​Reached when the rate of the forward reaction of a reversible reaction equals the rate of the backward reaction.
-The concentrations of the reactants and products
remain constant.

Question 7

Effect of changing concentration on equilibrium [2]

Answer 7

-If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
-If the concentration of
a product is decreased, more reactants will react until equilibrium is reached again

Question 8

Effect of changing pressure on equilibrium [2]

Answer 8

-​If pressure is increased, the position of equilibrium shifts towards the side with the fewest number of molecules.
- If the pressure is decreased, the position of equilibrium shifts towards the side with the greatest number of
molecules to oppose this change.

Question 9

Effect of changing temperature on equilibrium

Answer 9

​If the temperature of a system in equilibrium is increased, there will be an increase in the relative amount of products for an endothermic reaction and a decrease for an exothermic reaction

Question 10

Equilibrium [2]

Answer 10

​-A chemical state in which the forward and reverse reactions of a process occur at the same rate.
- This means there is no overall change in the concentrations of the reactants and
products.

Question 11

Equilibrium constant (K) [2]

Answer 11

​ ​-A value that relates the amount of products and reactants at
equilibrium in a reversible reaction at a specific temperature.
- K is unaffected by pressure and
presence of a catalyst but is affected by temperature.

Question 12

Indicator (give 2 common ones used in titrations ) [4]

Answer 12

-​Chemical solutions whose colour depends on the pH of the solution they are in.
-Methyl orange and phenolphthalein are indicators commonly used in titrations.
- Methyl orange is red in acid and yellow in alkali.
-Phenolphthalein is colourless in acid and pink in alkali

Question 13

K​c​ [3]

Answer 13

• ​A value that relates the concentrations of products and reactants present at equilibrium in a reversible reaction at a specific temperature.
• The equilibrium constant shows how much product and reactant there is at equilibrium. It’s found by dividing the concentration of the products by the concentration of the reactants, with each raised to the power of the number in front of them in the equation. ​ ​
  -Liquids and solids are not
  included in heterogeneous K​C​ expressions as their concentrations effectively remain constant

Question 14

K​p

Answer 14

​A value that relates the amounts of gaseous products and gaseous reactants present at
equilibrium ​in a reversible reaction at a specific temperature

Question 15

Le Chatelier’s principle

Answer 15

​If a reaction at equilibrium is subjected to a change in concentration, temperature or pressure, the position of equilibrium will move to counteract the change

Question 16

Mole fraction

Answer 16

the ratio of moles of a paricular gas to the total no. of moles of a gas present

Question 17

eqn for mole fraction

Answer 17

no. of moles of particular gas/ total no. of moles of all gases in mixture

Question 18

Neutralisation

Answer 18

​A reaction between an acid and a base to form water and a salt

Question 19

The ionic equation for neutralisation

Answer 19

H​+​(aq)​ + OH​-​(aq)​ → H​2​O​(l)

Question 20

Partial pressure

Answer 20

The pressure that would be exerted by one gas in a mixture if it occupied the container alone

Question 21

eqn of partial pressure

Answer 21

partial pressure of x= total pressure X mole fraction of x

Question 22

PH [4]

Answer 22

-​A value that represents the acidity or alkalinity of a solution.
-Acidic solutions have a pH of
less than 7
-while alkali solutions have a pH of greater than 7.
-Neutral solutions have a pH of 7

Question 23

Reversible reaction [2]

Answer 23

-A reaction in which the products from the reaction can react together to form the original reactants.
-The direction of a reversible reaction can be changed by changing
the conditions

Question 24

Strong acid [2]

Answer 24

An acid which dissociates/ionises almost completely in water.
-This means nearly all the H​+​ ions will be released

Question 25

Strong base

Answer 25

​A base which dissociates/ionises almost completely in water

Question 26

Titration

Answer 26

​An experimental technique used to determine​ the concentration of an unknown solution by using a second solution with a known concentration

Question 27

Weak acid

Answer 27

Acids which only dissociate/ionise very slightly in water so that only a small number of H​+​ ions are released

Question 28

Weak base

Answer 28

A base which only slightly dissociates/ionises in water