8 - Energetics I

Question 1

what are standard conditions

Answer 1

100kPa

298 K

Question 2

define standard enthalpy of combustion

Answer 2

change in enthalpy when one mole of a substance is completely oxidised in excess oxygen at standard conditions

Question 3

define standard enthalpy of formation

Answer 3

enthalpy change when 1 mole of a substance is formed from its elements in their standard states

Question 4

define standard enthalpy change of reaction

Answer 4

change in enthalpy when a reaction takes place in the molar quantities specified in the equation at standard conditions

Question 5

define lattice energy

Answer 5

enthalpy change when one mole of an ionic solid is formed from gaseous ions

Question 6

what has to be true for a compound to have covalent character?

Answer 6

the cation has a small radius and high charge

the anion has a large radius (and small charge)

Question 7

what makes something very soluble?

Answer 7

if the cation has a high charge (more important) and small radius (less important)

Question 8

define standard enthalpy of solution

Answer 8

enthalpy change when 1 mol of an ionic solid dissolves in excess water at standard conditions

Question 9

ΔS surroundings =

Answer 9

-ΔHr / T

Question 10

what does thermodynamically stable mean?

Answer 10

when ΔS < o, so cannot react

Question 11

what does kinetically stable mean?

Answer 11

when the activation energy hasn’t been reached yet, so the reaction can’t take place

Question 12

ΔG =

Answer 12

ΔHr - TΔS system

Question 13

when is the reaction feasible / spontaneous?

Answer 13

ΔG < 0 or ΔS total > 0