Thermodynamics

Question 1

define enthalpy change

Answer 1

amount of heat taken in or given out at constant pressure during any physical or chemical change

Question 2

define standard enthalpy change

Answer 2

change in enthalpy when reactants in their standard states form products that are also in their standard states

Question 3

define standard state

Answer 3

the state at a given temperature in its pure most stable form at 100kPa

Question 4

when do exothermic changes occur

Answer 4

when forces of attraction operate

Question 5

when do endothermic changes occur

Answer 5

when forces must be overcome/broken

Question 6

define enthalpy of formation

Answer 6

enthalpy change when 1 mol of a substance is formed from its constituent elements with all substances in their standard states

Question 7

define enthalpy of combustion

Answer 7

enthalpy change when 1 mol of substance undergoes complete combustion in O2 with all substances in their standard states

Question 8

define enthalpy of neutralisation

Answer 8

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

Question 9

define enthalpy of first ionisation

Answer 9

enthalpy change when each atom in 1 mol of gaseous atoms loses one electron to form one mol of gaseous 1+ ions

Question 10

define enthalpy of second ionisation

Answer 10

enthalpy change when each ion in 1 mol of gaseous 1+ ions loses one electron to form one mol of gaseous 2+ ions

Question 11

define enthalpy of first electron affinity

Answer 11

enthalpy change when each atom in 1 mol of gaseous atoms gains one electron to form one mol of gaseous 1- ions

Question 12

define enthalpy of second electron affinity

Answer 12

enthalpy change when each atom in one mol of gaseous 1- ions gains one electron to form one mol of gaseous 2- ions

Question 13

define enthalpy of atomisation

Answer 13

enthalpy change when one mol of gaseous atoms is produced from an element in its standard state

Question 14

define hydration enthalpy

Answer 14

enthalpy change when 1 mol of gaseous ions become hydrated ( dissolved in water)

Question 15

define enthalpy of solution

Answer 15

enthalpy change when 1 mol of ionic solid dissolves in amount of water large enough that dissolved ions are well separated and do not interact with each other

Question 16

define bond dissociation enthalpy

Answer 16

enthalpy change when 1 mol of covalent bonds are broken in the gaseous state

Question 17

define lattice enthalpy of formation

Answer 17

enthalpy change when 1 mol of a solid ionic compound is formed from its constituent ions in the gaseous phase

Question 18

define lattice enthalpy of dissociation

Answer 18

enthalpy change when 1 mol of a solid ionic compound is broken up into its constituent ions in the gas phase

Question 19

define enthalpy of vaporisation

Answer 19

enthalpy change when 1 mol of liquid is turned into gas

Question 20

define enthalpy of fusion

Answer 20

enthalpy change when 1 mol of a solid is turned into a liquid

Question 21

is enthalpy of formation endo of exothermic

Answer 21

mostly exothermic

Question 22

is enthalpy of combustion endo or exothermic

Answer 22

exothermic

Question 23

is enthalpy of neutralisation exo or endothermic

Answer 23

exothermic

Question 24

is enthalpy of ionisation endo or exothermic

Answer 24

endothermic

Question 25

is enthalpy of first electron affinity endo or exothermic

Answer 25

exothermic

Question 26

is enthalpy of second electron affinity endo or exothermic

Answer 26

endothermic

Question 27

is enthalpy of atomisation endo or exothermic

Answer 27

endothermic

Question 28

is enthalpy of hydration endo or exothermic

Answer 28

exothermic

Question 29

is enthalpy of solution endo or exothermic

Answer 29

varies

Question 30

is bond dissociation enthalpy endo or exothermic

Answer 30

endothermic

Question 31

is lattice enthalpy of formation endo or exothermic

Answer 31

exothermic

Question 32

is lattice enthalpy of dissociation exo or endothermic

Answer 32

endothermic

Question 33

is enthalpy of vaporisation endo or exothermic

Answer 33

endothermic

Question 34

is enthalpy of fusion endo or exothermic

Answer 34

endothermic

Question 35

what unknown enthalpy does a born-Haber cycle usually calculate

Answer 35

lattice enthalpy

Question 36

common mistakes to make in Born-Haber cycles

Answer 36

using wrong enthalpy changes not multiplying by molar amounts not taking care with signs

Question 37

what does enthalpy of formation equal in most Born-Haber cycles

Answer 37

sum of all other enthalpy values

Question 38

what do theoretical values for lattice enthalpies assume

Answer 38

perfect ionic model - all ions in an ionic compound are perfectly spherical

Question 39

are positive ions better at distorting negative ions when they're larger or smaller, and with a higher or lower charge

Answer 39

small. higher charge.

Question 40

are negative ions easier to distort when they're larger or smaller, and a higher or lower

Answer 40

larger and higher charge

Question 41

are ionic compounds with covalent characters more or less soluble in water

Answer 41

less soluble

Question 42

do ionic compounds with covalent characters have a higher or lower than expected melting point

Answer 42

lower than expected

Question 43

do ionic compounds with covalent character have higher or lower electrical conductivity than expected

Answer 43

lower than expected

Question 44

define magnitude of lattice enthalpy

Answer 44

overall strength of ionic bonding

Question 45

what does the difference between experimental and theoretical values in Born-Haber calculations mean

Answer 45

the larger the difference the more covalent character the ions possess

Question 46

are water molecules polar or nonpolar

Answer 46

polar

Question 47

is water attracted to anions, cations or neither

Answer 47

anions and cations

Question 48

is the hydration enthalpy larger or smaller for an ion with a higher charge-to-size ratio

Answer 48

larger

Question 49

what is entropy a measure of

Answer 49

the amount of disorder in a system

Question 50

when is the entropy value always zero

Answer 50

at 0K in a perfectly ordered crystal

Question 51

is enthalpy of the universe always increasing or decreasing

Answer 51

increasing

Question 52

what makes entropy increase

Answer 52

increase in temperature from solid to liquid to gas from simple to more complex molecules

Question 53

define feasible (spontaneous) change

Answer 53

one that has a natural tendency to occur without being driven by external influences

Question 54

at what free Gibbs energy value is a reaction at equilibrium

Answer 54

0

Question 55

at what free Gibbs value is a reaction feasible

Answer 55

deltaG

Question 56

how to find a feasible temperature at which a reaction can happen

Answer 56

set the free Gibbs value to 0 and solve for T

Question 57

Gibbs free energy equation symbol equation

Answer 57

deltaG = deltaH - TdeltaS

Question 58

acronym???? to remember Gibbs free energy equation

Answer 58

Grapes Have Tiny Seeds

Question 59

word equation for Gibbs free energy

Answer 59

Gibbs free energy change = enthalpy change - temperature X entropy change

Question 60

units for numbers used in Gibbs free energy equation

Answer 60

Gibbs free energy change in kJ/mol enthalpy change in kJ/mol temperature in Kelvin entropy change in J/K/mol

Question 61

general graphical equation of Gibbs free energy

Answer 61

y = mx+c