7.2. Energetics 2

Question 1

enthalpy change of a reaction =

Answer 1

enthalpy of formation (products) - enthalpy of formation (reactants)

Question 2

is there a change is enthalpy if only the intermolecular bonds are broken?

Answer 2

yes, the enthalpy of formation is different for different states of the same compound

Question 3

Born-Haber cycle equation

Answer 3

enthalpy of formation = enthalpy of sublimation + first ionization enthalpy + first electron affinity + enthalpy of disssociation + lattice energy (MX example)

Question 4

standard enthalpy change of atomisation

Answer 4

the enthalpy change when one mole of atoms in a gasous state is formed from the element in its standard state
- (delta)Hat

Question 5

first electron affinity

Answer 5

the enthalpy change when one mole of gaseous atoms each gain one electron
- (delta)HEa

Question 6

first ionization enthalpy

Answer 6

the enthalpy change when one mole of gaseous 1+ ions are formed from one mole of gaseous atoms
- (delta)Hi(1)

Question 7

lattice enthalpy

Answer 7

the enthalpy change when one mole of solid ionic compound is made from gaseous ions - it increases with the charge of ions and increases with the decreasing size of ions
- (delta)HLE

Question 8

the greater the charges of ions,…

Answer 8

the greater the E holding them together (lattice E)

Question 9

spontaneous reactions/processes

Answer 9

• generally exothermic
• the final state is more disordered/random than the original => (delta)S>0

Question 10

spontaneity is related to ___, and the thermodynamic property related to ___ is…

Answer 10

an increase in randomness,
randomness,
entropy (S) [J/Kmol)

Question 11

entropy increases with:

Answer 11

1) state (g>l>s)
2) temperature (less than state)
3) molecular complexity
4) depending on coulombic attractions

Question 12

(delta)S=

Answer 12

S(products) - S(reactants)

Question 13

when is a reaction spontaneous (relating to (delta)H and (delta)S?
(table)

Answer 13

H<0, S>0 - spontaneous
H<0, S<0/H>0, S>0 - depends on magnitudes (more favorable in lower T/more favorable in higher T)
H>0, S<0 - not spontaneous

Question 14

(delta)S<0/>0 meaning

Answer 14

<0 = more order
>0 = less order (characteristic of spontaneous reactions)

Question 15

-(delta)H (system) is proportional to…
*

Answer 15

(delta)S (surroundings) - an exothermic process has (delta)S (surroundings)>0

Question 16

Gibbs free E change =

Answer 16

total E change for the system ((delta)H (system)) - E lost in disordering the system (T*(delta9S (system))

Question 17

when is a reaction P and when R-favored (relating to Gibbs free E change, (delta)H and (delta)S)?
(table)

Answer 17

1) H<0, S>0 => G<0 (P-favored, spontaneous)
2) H>0, S<0 => G>0 (R-favored, not spontaneous)
3) H, S<0 / H, S>0 - depends on T values (spontaneous at low T(spontaneous at high T)

Question 18

Gibbs free E change for an element is…

Answer 18

zero

Question 19

(delta)G>/<0 meaning
*

Answer 19

(delta)G<0 => spontaneous, enthalpy driven
(delta)G>0 => not spontaneous, entropy driven

Question 20

(delta)G (reaction) =

Answer 20

(delta)G (products) - (delta)G (reactants)