Oceans

Question 1

why do ionic substances only dissolve in polar solvents?

Answer 1

non polar molecules don’t interact with the ions enough to disturb the electrostatic forces in the lattice.

Question 2

what is lattice enthalpy

Answer 2

• gaseous to solid
• enthalpy when 1 mole of ionic lattice is formed from its gaseous ions under standard conditions.
• exothermic
• more -ve = stronger bonds

Question 3

what is the enthalpy of hydration

Answer 3

• when 1 mole aqueous ions is formed from gaseous ions

- exothermic

Question 4

what is enthalpy solution?

Answer 4

• enthalpy change when 1 mole of an ionic substance dissolves to form an infinitely dilute solution (as much dissolves as possible)

Question 5

enthalpy level diagrams

Answer 5

• gaseous ions on the top always
• solid (solute) always in the middle below gaseous ions
• solution will either go below solid is exothermic
• or above solid if endothermic.
  1. /\hyd goes from gaseous to solution
  2. -/\LE is from solid to gaseous
  3. /\sol is from solute to solution funnily enough

Question 6

what do -/\sol values suggest. what do +/\sol values suggest?

Answer 6

positive= endothermic = doesn't normally dissolve
negative= exothermic = dissolves normally

Question 7

what is charge density?

Answer 7

• charge / ion radius
• electrostatic forces are higher in lattices with a higher CD
• more exothermic
• charge density will decrease going down the periodic table as the charge stays the same but the size increases. Going across the charge density increases going to the right as the charge increases and the size decreases.

Question 8

what is entropy?

Answer 8

a measure of the ways particles can be rearranged

- substances more stable with more disorder so will move to the side with more entropy

Question 9

factors affecting entropy?

Answer 9

1. solids have a lower entropy as its a fixed state so will move to the side with gases or liquids
2. the more energy the more entropy so will move
3. the more particles the more disorder so will move again

Question 10

what are the entropy equations?

Answer 10

1. /\totS= /\sys + /\surr
2. /\sys = Sprod - Sreact
3. /\surr= - (/\H/T)

to be feasible, /\tot is +ve or 0
if /\sys is -ve then /\surr needs to be as positive or larger that /\sys to still be feasible

Question 11

solubility=?

Answer 11

solubility (gdm-3) /mr

Question 12

what is the bronsted-lowry theory?

Answer 12

• acids are proton donors
• bases are proton acceptors
• strong acids fully dissociate into their ions
• weak acids don’t= equilibrium
• HA = H* + A-
• conjugate pairs accept and donate protons

Question 13

pH calculations?

Answer 13

pH= -log10 [H*]
[H*] = 10-pH
Kw= Kc = [H*] [OH-] / [H2O]
pka= -log[ka]
ka= 10-pka

Question 14

what is a buffer?

Answer 14

resists change in pH when an acid or base is added.

• the weak acid partly dissociates whereas the salt fully dissociates.
• acid added, protons build up salt accepts them to make weak acid to shift equilibrium

Question 15

buffer equations?

Answer 15

[H*]= Ka x [HA]/ [A-]
Ka= [H*] [A-] / [HA]
pH= -log10 [H*]

Question 16

greenhouse effect?

Answer 16

1. sun emits EMR, mostly IR and UV
2. atmospheric gases absorb and reflect some
3. radiation absorbed causes earth to warm up
4. greenhouse gases= CH4 and CO2
5. found in troposphere absorb IR
6. increase vibrational energy
7. molecules collide and KE increases
8. rasies the temperature
9. gases re-emit radiation which is reabsorbed.