thermodynamics

Question 1

what is the enthalpy of formation?

Answer 1

enthalpy change when one mole of a substance is formed from its elements with all substances in their standards states

Question 2

what is enthalpy of combustion?

Answer 2

enthalpy change when one mole of a substance is burned in excess oxygen with all substances in their standard states

Question 3

what is enthalpy of neutralisation?

Answer 3

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

Question 4

what is ionisation enthalpy?

Answer 4

first ionisation energy is the enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions

Question 5

what is electron affinity?

Answer 5

first electron affinity is the enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions

Question 6

what is enthalpy of atomisation?

Answer 6

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

Question 7

what is hydration enthalpy?

Answer 7

enthalpy change when one mole of gaseous ions becomes hydrated - dissolved in water

Question 8

what is enthalpy of solution?

Answer 8

enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other

Question 9

what is bond dissociation enthalpy?

Answer 9

enthalpy change when one mole of covalent bonds is broken in the gaseous state

Question 10

what is lattice enthalpy of formation?

Answer 10

enthalpy change when one mole of a solid ionic compound is formed from its ions in the gas phase

Question 11

what is lattice enthalpy of dissociation?

Answer 11

enthalpy change when one mole of a solid ionic compound is broken up into its ions in the gas phase

Question 12

what is enthalpy of vaporisation?

Answer 12

enthalpy change when one mole of a liquid is turned into a gas

Question 13

what are the two ways of calculating lattice enthalpy values?

Answer 13

experimental and theoretical

Question 14

how is the theoretical value calculated?

Answer 14

considering the size, charge and arrangement of ions
suggests the ions are perfect spheres

Question 15

which is the real lattice enthalpy value?

Answer 15

the experimental value

Question 16

what makes ions have covalent character?

Answer 16

if there is distortion of the ions as this means they are not perfectly spherical

Question 17

what are the characteristics of compounds that have some covalent character?

Answer 17

they are insoluble in water and have lower melting points than expected and electrical conductivity may be lower than expected

Question 18

what does a big difference between the experimental and theoretical values mean?

Answer 18

the greater the difference is, the greater the covalent character of the compound

Question 19

what does the magnitude of lattice enthalpy show?

Answer 19

indicates the overall strength of the ionic bonding

Question 20

what does the arrow structure look like for working out the enthalpy of solution?

Answer 20

gas ions
^ ^
formation / \hydration
/ \
ionic solid ————-> dissolved ions
solution

Question 21

what is entropy a measure of?

Answer 21

disorder

Question 22

what is the symbol for entropy?

Answer 22

(S)

Question 23

how can you increase entropy the most?

Answer 23

by changing state

Question 24

what factors affect entropy?

Answer 24

— physical state
— dissolution
— number of particles

Question 25

how do you calculate the change in entropy?

Answer 25

change in entropy = ((S) of products) - ((S) of reactants)

Question 26

what does a +ve entropy value show?

Answer 26

there is an increase in entropy`

Question 27

what is the equation for /\G?

Answer 27

/\G = /\H - (T x (/\S/1000)

Question 28

what value does /\G have to be to mean the reaction is feasible?

Answer 28

/\G must be negative for the reaction to be feasible

Question 29

when there is a change of state, what does /\G = ?

Answer 29

/\G = 0 when there is a change in state

Question 30

how do you work out the temperature at which a reaction is feasible?

Answer 30

T = /\H / (/\S / 1000)