thermodynamics

Question 1

What does Hess’ law state

Answer 1

the enthalpy change of a reaction is independent of the route taken

Question 2

define standard enthalpy of formation

Answer 2

the enthalpy change when one mole of a compound is formed from its constituent elements in standard conditions, with all products and reactants in their standard states

Question 3

what is the standard enthalpy of an element

Answer 3

0

Question 4

define standard enthalpy of combustion

Answer 4

the enthalpy change when one mole of a substance is completely burnt in excess oxygen

Question 5

define standard enthalpy of atomisation

Answer 5

enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions

Question 6

define first ionisation energy

Answer 6

enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 7

define second ionisation energy

Answer 7

enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 8

define first electron affinity

Answer 8

enthalpy change when one mole of gaseous atoms gain one mole of electrons to form one mole of gaseous 1- ions

Question 9

define second electron affinity

Answer 9

enthalpy change when one mole of gaseous 1- ions gains one mole of electrons to form one mole of gaseous 2- ions.

Question 10

define lattice enthalpy of formation

Answer 10

enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions.

Question 11

define lattice enthalpy of dissociation

Answer 11

enthalpy change when one mole of solid ionic lattice is dissociated into its gaseous ions

Question 12

define enthalpy of hydration

Answer 12

enthalpy change when one mole of gaseous ions become hydrated/dissolved in water to infinite dilution

Question 13

define enthalpy of solution

Answer 13

enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution.

Question 14

define mean bond dissociation enthalpy

Answer 14

enthalpy change when one mole of covalent bonds is broken, with all species in the gaseous state

Question 15

what is a born haber cycle

Answer 15

thermochemical cycle showing all the enthalpy changes involved in the formation of an ionic compound. start with elements in their standard state.

Question 16

what factors affect the lattice enthalpy of an ionic compound

Answer 16

size of the ion

charge of the ion

Question 17

how can you increase the lattice enthalpy

Answer 17

smaller ion

charge centres will be closer together increasing the charge. increased electrostatic forces of attraction.

Question 18

how can born haber cycles be used to see if compounds could theoretically exists

Answer 18

use known data to predict certain values and then see if these compounds would be thermodynamically stable.

Question 19

what happens when a solid is dissolved in terms of interactions of the ions with water

Answer 19

break lattice
gaseous ion, dissolve
surrounded by water

Question 20

what is the perfect ionic model

Answer 20

perfectly spherical
even charge distribution
no covalent character

Question 21

what kind of bonds will be the most ionic

Answer 21

between large positive ions and small negative ions

Question 22

define spontaneous and feasible

Answer 22

it will take place of its own accord

Question 23

is a reaction with a positive or negative enthalpy change more likely to be spontaneous

Answer 23

negative

Question 24

define entropy

Answer 24

randomness of a system

Question 25

units of entropy

Answer 25

JK-1mol-1

Question 26

what is the second law of thermodynamics

Answer 26

entropy always increases, as it is overwhelmingly more likely for molecules to be disordered than ordered

Question 27

is a reaction with positive or negative entropy change more likely to be spontaneous

Answer 27

positive

Question 28

compare the general entropy for solids, liquids and gases

Answer 28

solids < liquids < gases

Question 29

how do you calculate the entropy change for a reaction

Answer 29

sum of products entropy - sum of reactants entropy

Question 30

gibbs free energy

Answer 30

delta G = delta H - Tdelta S

Question 31

what does gibbs free energy show

Answer 31

if delta G < / = 0 then the reaction is feasible

Question 32

why is entropy 0 at 0K

Answer 32

no disorder