physical chem and transition elements

Question 1

how would the lattice enthalpies of magnesium chloride and calcium chloride differ?

Answer 1

lattice enthalpy of MgCl2 is more eco than CaCl2
because Mg2+ is smaller and has greater charge density
therefore attraction between Mg2+ and Cl- is greater

Question 2

explain what is meant by the enthalpy change of hydration

Answer 2

1 mole of gaseous ions react to form hydrated ions

Question 3

predict how the enthalpy changes of hydration of F- and Cl- differ

Answer 3

F- more exo
F- has smaller size
F- has greater attraction to H2O

Question 4

explain what is meant by the term average bond enthalpy

Answer 4

breaking of one mole of bonds in gaseous molecules

Question 5

what is meant by a heterogeneous equilibrium?

Answer 5

species have different states

Question 6

what are the standard conditions to measure standard cell potential?

Answer 6

1 mol dm3 solutions
298K
101 kPa pressure

Question 7

Explain which block in the periodic table sodium and magnesium belong to

Answer 7

S block
outer electron is in a s orbital

Question 8

Explain why the first ionisation energy of sodium is more endothermic than that of potassium

Answer 8

Sodium has fewer shells
Nuclear attraction increases

Question 9

Explain why the lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide

Answer 9

Na+ is smaller
Has stronger attraction to O2-

Question 10

Explain why combustion has a negative enthalpy change

Answer 10

More energy released by forming bonds than required to break bonds

Question 11

state the definition of electron affinity

Answer 11

energy change when one mole of electrons is gained
by one mole of gaseous atoms of an element to form one mole of gaseous 1- ions
under standard conditions

Question 12

define the term lattice enthalpy

Answer 12

the formation of one mole of an ionic lattice
from its gaseous ions
under standard conditions

Question 13

on a born haber cycle, why do the arrows for 1st and 2nd electron affinity point in different directions?

Answer 13

1st is exo
2nd is endo
because repulsion between electron and negative ion requires a large amount of energy to overcome

Question 14

what is meant by the half life of a reaction?

Answer 14

Time for concentration (of reactant) to fall to half original value

Question 15

use the Boltzmann distribution graph to explain how increasing the temperature increases the rate of reaction

Answer 15

at a higher temp more molecules have energy above activation energy

Question 16

suggest how the concentration of the bromine could have been monitored

Answer 16

measure reduction of colour of bromine

Question 17

why would use of excess HCOOH ensure that the order with respect to HCOOH is effectively zero

Answer 17

conc of HCOOC would be constant

Question 18

explain how a student could determine the activation energy for a reaction using values of k and T

Answer 18

plot graph using ln k and 1/T
measure gradient
Ea = -R x gradient or -8.314 x gradient

Question 19

suggest 2 observations that would confirm that all of a metal has reacted

Answer 19

effervescence stops
metal dissolved

Question 20

plan how a student could prepare 250cm3 of a standard solution

Answer 20

dissolve mass of the solid in distilled water in a beaker

transfer solution to a 250cm3 volumetric flask and ensure that all solution is washed out of beaker

make up solution to 250cm3 with distilled water and ensure thorough mixing by inverting the flask several times

Question 21

observation when aqueous sodium hydroxide is added to Fe2+

Answer 21

green ppt

Question 22

when a student prepares a buffer solution, the volume of solution increases slightly

suggest whether the pH of the buffer solution would be the same, greater than, or less

Answer 22

same
ratio is the same

Question 23

Red blood cells contain haemoglobin.
Explain using ligand substitutions:
• how haemoglobin transports oxygen around the body
• why carbon monoxide is toxic.

Answer 23

Oxygen coordinately/ datively bonds w iron/ Fe2+

O2 is replaced by H2O or CO2

CO forms stronger bonds than O2

Question 24

What is correct for a neutral solution at any temperature?

Answer 24

[H+] = [OH−]

Question 25

explain what is meant by enthalpy change of solution

Answer 25

1 mole of a compound/ substance/ solid/ solute dissolving

Question 26

explain why it is difficult to predict whether the enthalpy change of solution becomes more exo or less exo down the group from MgF2 to MgI2

Answer 26

halide ion gets larger down the group lattice enthalpy is less exo down the group/ halide ion has less attraction for Mg2+ hydration enthalpy is less exo down the group/ halide ion has less attraction for H2O difficult to predict whether lattice enthalpy or hydration enthalpy has bigger effect

Question 27

what is meant by a bidentate ligand

Answer 27

donated 2 e- pairs and forms 2 coordinate bonds

Question 28

state 1 important feature of a fuel cell that is different from a conventional storage cell

Answer 28

fuel cell reacts w oxygen to give electrical energy requires continuous supply of fuel and oxygen

Question 29

state features of a dynamic equilibrium

Answer 29

exists in a closed system rate of forwards reaction = rate of backwards reaction concentrations/ pressure/ temp are constant/ do not change

Question 30

enthalpy change of formation definition

Answer 30

enthalpy change when 1 mole of a substance is formed from its elements in their normal state under standard conditions

Question 31

enthalpy change of combustion definition

Answer 31

enthalpy change when 1 mole of a substance is completely burned in an excess of Oxygen under standard conditions

Question 32

enthalpy change of neutralisation definition

Answer 32

enthalpy change when 1 mole of water is formed in a reaction between an acid and a base under standard conditions

Question 33

how can an aqueous solution of an acid contain hydroxide ions

Answer 33

water dissociates/ ionises

Question 34

explain why a buffer solution is formed

Answer 34

show equation forming salt of conjugate base weak acid remains/ is in excess

Question 35

ligand definition

Answer 35

Donates a lone pair to metal ion Forms dative covalent (coordinate) bond with metal ion

Question 36

Kc can be calculated using the moles of components in the equilibrium mixture why?

Answer 36

Volume cancels OR Same number of moles on each side of equation

Question 37

a student suggests that water is neutral explain why they r correct

Answer 37

(In pure water), [H+] (always) equals [OH–]

Question 38

explain what is meant by the term mono basic acid

Answer 38

One mole of acid donates/dissociates to form one mole of protons/H+

Question 39

when a small vol of water is added to a buffer sol, pH doesn't change explain why

Answer 39

ratio/proportion [HA]/[A–] is the same

Question 40

explain the term entropy

Answer 40

a measure of the dispersal of energy (in a system) or a measure of the disorder (of a system)

Question 41

in a conc time graph, using collision theory, explain why the gradient decreases over time

Answer 41

(Over time) concentration decreases AND collisions are less frequent