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chemistry > module 5 HSC > Flashcards

module 5 HSC Flashcards

what happens when chemical reactions do not go through to completion

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1
Q

irreversible reaction + an example

A

reactant forms products which cannot be reverted back to reactants
eg. combustion reactions eg. magnesium and steel wool

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2
Q

reversible reactions + example

A

products that were once formed hat can react again to form reactants
eg. cobalt (II) chloride hexahydrate (dark pink) –> chloride dihydrate (purple)

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3
Q

combustion of magnesium and stee wool

A

do with steel wool and repeat for magnesium strip

  • white solid forms when magnesium heated –> ice bath no changes
  • reddish brown solid forms when wool is heated –> ice bath no changes
  • shows irreversibility
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4
Q

closed system

A

only energy can be exchanged with the surroundings where there is no matter transfer

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5
Q

open system

A

both matter and energy can be exchanged with the surroundings

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6
Q

static equilibrium

A

rates of forward and reverse reaction are equal and zero
eg. at completion: dissolution of unsaturated solution
eg. before initiation: combustion without initial spark
eg. reversible but with insurmountable activation energy: diamond to graphite

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7
Q

dynamic equilibrium

A

rate of forward reaction are equal and non zero
- concentration is constant

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8
Q

advantages + disadvantages of molecular modelling kits

A

ad:
-helps visualise complex phenomenon
- demonstrated both static and dynamic equilibrium well

dis:
-bond are rigid so we cant see electrons moving
- doesnt show transfer of energy

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9
Q

advantages of modelling dynamic equilibrium

A
  • check
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10
Q

enthalpy

A

internal energy of a system
- only measures the change
delta H = sum of products - sum of reactants

eg. combustion of fuel
exothermic = forward enthalpy drive
endo thermic = reverse enthalpy drive

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11
Q

exothermic reaction is what type of drive

A

forward enthalpy drive

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12
Q

endothermic reaction is what type of drive

A

reverse enthalpy drive

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13
Q

entropy

A

measure of the state of disorder within a chemical system
- absolute can be measured

s> 0 = forward entropy drive
s< 0 = reverse entropy drive

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14
Q

difference between enthalpy and entropy

A

enthalpy can only measure change in enthalpy whereas entropy can measure absolute entropy

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15
Q

entropy and enthalpy for photosynthesis

A

6CO2 + 6H2O –> C6H12O6 + 6O2
s < 0 as ordered glucose molecules are created (reverse entropy drive)

h>0 = reverse entropy drive as energy is absorbed from surrounding

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16
Q

reversible reactions and delta G

A

reversible reactions tend to have completing enthalpy and entropy drives

G>0 = non-spontaneous
h>0, s<0 eg. photosynthesis

G<0 = spntaneous
h<0, s> 0 eg. combustion

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17
Q

combustion entropy and enthalpy

A

s>0 –> more heat = more disorder –> forward entropy drive

H<0 –> energy released –> forward enthalpy drive

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18
Q

collision theory

A

chemical reactions take place when molecules with sufficient energy collide with correct orientation
- increases rate of reaction due to the increase in the frequency of collisions
- initially concentration of reactants
- reactant particles collide at high frequency
- rate of reactants converted to products is high
- concentration of reactants decrease as they are converted to products
- rate of forward reaction decreases as products are formed the product concentration increases
- increased frequency of collisions of products
- rate of reverse reaction increases
- continues until forward and reverse are equal

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19
Q

le chateliers principle

A

if a system at dynamic equilibrium is disturbed, then the system will shift as to minimise the change until a new equilibrium is reached

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20
Q

temperature lcp

A

increase temp -> increase rate of reaction -> proportion of molecules with enough energy to overcome the activation energy barrier increases –. increases collision frequency
- has a greater effect on reaction rate when reaction rate is high as a greater relative proportion of molecules have enough energy to overcome barrier
- since forward reaction has a higher activation energy -> teh rate of the forward reaction is increased where the endo is favoured

21
Q

lines for graphs

A

straight drop = concentration
gradual = temperature
volume change = straight line
catalyst = increased rate of reaction

22
Q

equilibrium constant

A

products / reactants

23
Q

Q vs K

A

Q>K = proceed left
Q=K dynamic equilibrium
Q<K proceed right

24
Q

only factor that can change K

A

temperature

25
Q

manipulating equilibrium constant

A

reciprocal (k) = reversing reaction

doubled (k) = coeffs doubled

multiply (k’s) = two reactions added together

26
Q

catalyst

A

provides an alternate pathway with a lower activation energy for both forward and reverse reactions
- does not change concentrations or equilibrium just hastens the attainment of equilibrium
- does not impact the keq

27
Q

practical for keq

A

iron (III) thiocynate

fe3+ + SCN- ->-< [FeSCN] 2+

H<0

Fe3+ = yellow
SCN - = colourless
[FeSCN]2+ = blood red

adding sodium hydroxide –> make the solution lighter in colour as the Fe3+ is precipitate out

28
Q

look at colourmetry

A
29
Q

gibbs free energy

A

delta G = delta H - Temperature (delta S)
- T in kelvin

G>0 non-spontaneous
G<0 spontaneous

large negative H = keq larger

30
Q

enthalpy and keq relationship

A

larger H keq = smaller
smaller H keq = larger

31
Q

when does a solute dissolve

A

when the formation of intermolecular forces between solvent and solutes are more favourable than the existing intermolecular forces

32
Q

ionic compounds dissociation

A

individual ions form ion-dipole forces with water

  • solute-solute interactions are overcome endothermic (ionic bonds in salts, ionic lattice held together by ionic bonds is broken)
  • solvent-solvent interactions overcome endothermic (dipole-dipole interactions, hydrogen bonding, dispersion forces)

ion-dipole forces formed exothermic
- formed during solvation
- solvent molecules form concentric rings called hydration spheres around individual ions
- ion-dipole forces are formed between ions and water molecules

33
Q

salt that dissolves exothermically

A

NaOH

34
Q

salt that dissolves endothermically

A

KCl

35
Q

dissolution is vs dissociation

A

process of solute dissolving in solvent and it is a physical change

separation of ions that occurs when a solid ionic compound dissolves

36
Q

what does dis

A
37
Q

what

A
38
Q

what does dissolution lead to

A

increased entropy as hydrated ions move freely in contrast to fixed ionic lattice

39
Q

dissolution as an equilibrium

A

static equilibrium : unsaturated
dynamic equilibrium: saturated

unsaturated solution: more can be dissolved

saturated solution: no more can be dissolved

supersaturated solution:
- allows for more solute to be dissolved

40
Q

concentration of saturated solution

A

> 10 soluble
1-10 partially soluble
<10 insoluble

41
Q

cycad

A
  • contains toxin cycasin C8H16N2O7
  • carcinogenic and neurotoxic
42
Q

how to detoxify cycad

A
  • strip off outer layer
  • seed crushed to increase surface area

two methods:
roast then
- submerge in boiling water to leach out to remove water-soluble toxins + ferments till no longer toxic

leach for longer periods time

then:
- water drained
-resultant extracted
- starch is dried and pounded into a fine powder again
- leached again to remove more toxins

43
Q

explain cycads with solubility equilibrium

A
  • cycasin is readily soluble in water 56.6g
  • when leeched in water the solid toxin dissolves and reaches dynamic equilibrium
  • boiling increases reaction rate due to the increased temperature

C8H16N2O7 (s) –> (equilibrium) C8H16N2O7 (aq)

44
Q

cobalt chloride

A

cobalt chloride hexahydrate is reversible
- endothermic
Co(H2O)6 2+ (aq) + HCL - (aq) -><. CoCl4 2- (aq) + 6H2O (l)

45
Q

precipitation

A

involves two solutions mixing together that results in the formation of an insoluble solid which is the precipitate

46
Q

mass of solute (units)

A

g/100ml

47
Q

molar concentration of salt (units)

A

mol L-1

48
Q

ionic product

A

QSP : concentrations that are not necessarily at equilibrium

QSP < KSP : unsaturated
QSP = KSP : saturated
QSP > KSP : supersaturated

49
Q

NAGSAG

A

nitrate
acetate
group 1
sulfate except CASTROBAR
ammonium
group 7 except toxic trio

chemistry (9 decks)

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