module 5 HSC

Question 1

irreversible reaction + an example

Answer 1

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

Question 2

reversible reactions + example

Answer 2

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

Question 3

combustion of magnesium and stee wool

Answer 3

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

Question 4

closed system

Answer 4

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

Question 5

open system

Answer 5

both matter and energy can be exchanged with the surroundings

Question 6

static equilibrium

Answer 6

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

Question 7

dynamic equilibrium

Answer 7

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

Question 8

advantages + disadvantages of molecular modelling kits

Answer 8

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

Question 9

advantages of modelling dynamic equilibrium

Answer 9

• check

Question 10

enthalpy

Answer 10

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

Question 11

exothermic reaction is what type of drive

Answer 11

forward enthalpy drive

Question 12

endothermic reaction is what type of drive

Answer 12

reverse enthalpy drive

Question 13

entropy

Answer 13

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

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

Question 14

difference between enthalpy and entropy

Answer 14

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

Question 15

entropy and enthalpy for photosynthesis

Answer 15

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

Question 16

reversible reactions and delta G

Answer 16

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

Question 17

combustion entropy and enthalpy

Answer 17

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

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

Question 18

collision theory

Answer 18

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

Question 19

le chateliers principle

Answer 19

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

Question 20

temperature lcp

Answer 20

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

Question 21

lines for graphs

Answer 21

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

Question 22

equilibrium constant

Answer 22

products / reactants

Question 23

Q vs K

Answer 23

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

Question 24

only factor that can change K

Answer 24

temperature

Question 25

manipulating equilibrium constant

Answer 25

reciprocal (k) = reversing reaction doubled (k) = coeffs doubled multiply (k's) = two reactions added together

Question 26

catalyst

Answer 26

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

Question 27

practical for keq

Answer 27

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

Question 28

look at colourmetry

Question 29

gibbs free energy

Answer 29

delta G = delta H - Temperature (delta S) - T in kelvin G>0 non-spontaneous G<0 spontaneous large negative H = keq larger

Question 30

enthalpy and keq relationship

Answer 30

larger H keq = smaller smaller H keq = larger

Question 31

when does a solute dissolve

Answer 31

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

Question 32

ionic compounds dissociation

Answer 32

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

Question 33

salt that dissolves exothermically

Answer 33

NaOH

Question 34

salt that dissolves endothermically

Answer 34

KCl

Question 35

dissolution is vs dissociation

Answer 35

process of solute dissolving in solvent and it is a physical change separation of ions that occurs when a solid ionic compound dissolves

Question 36

what does dis

Question 37

what

Question 38

what does dissolution lead to

Answer 38

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

Question 39

dissolution as an equilibrium

Answer 39

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

Question 40

concentration of saturated solution

Answer 40

>10 soluble 1-10 partially soluble <10 insoluble

Question 41

cycad

Answer 41

- contains toxin cycasin C8H16N2O7 - carcinogenic and neurotoxic

Question 42

how to detoxify cycad

Answer 42

- 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

Question 43

explain cycads with solubility equilibrium

Answer 43

- 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)

Question 44

cobalt chloride

Answer 44

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

Question 45

precipitation

Answer 45

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

Question 46

mass of solute (units)

Answer 46

g/100ml

Question 47

molar concentration of salt (units)

Answer 47

mol L-1

Question 48

ionic product

Answer 48

QSP : concentrations that are not necessarily at equilibrium QSP < KSP : unsaturated QSP = KSP : saturated QSP > KSP : supersaturated

Question 49

NAGSAG

Answer 49

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