Module 5

Question 1

Compare Static and Dynamic equilibrium.

Answer 1

At both static and dynamic equilibrium concentrations of both reactants and products remain stable. At dynamic equilibrium, the rate of both the forward and reverse reactions is equal, whereas at static equilibrium the rates of both the forwards and reverse reactions are 0. Static equilibrium is present in an irreversible reaction whereas dynamic equilibrium is present in a reversible reaction.

Question 2

Compare open and closed systems.

Answer 2

Both systems allow energy to pass from the system to the surrounding. However, a closed system does not allow matter to enter or escape, whereas an open system does.

Question 3

Analyse the effect of Photosynthesis on entropy and enthalpy.

Answer 3

6CO2(g) + 6H2O(l) –(sunlight & chlorophyll)–> C6H12O6(aq) + 6O2(g)

ΔH > 0 due to need for sunlight
ΔS < 0 (more order)

Question 4

What is Le Chatelier’s Principle?

Answer 4

Le Chatelier’s Principle is a principle which states that if a chemical system at equilibrium is disturbed by changing conditions, the system will shift equilibrium in order to minimise the effect of the disturbance and attain a new equilibrium.

Question 5

Cobalt(II) chloride hydrated and dehydrated

Answer 5

6H2O + CoCl2 CoCl2.6H20

Blue Pink

Question 6

Effects of temp, concentration, volume and/or pressure on Nitrogen dioxide and dinitrogen tetroxide equilibrium.

Answer 6

2NO2(g) N2O4(g)
Brown Colourless

• If you ^ temp, ⇌ will shift left to favour endo > goes brown
• if you ^ [N2O4] at a constant pressure, ⇌ will shift left to favour production of more NO2 (goes brown)
• if you ^ pressure ⇌ shifts to favour N2O4 as there are fewer gaseous moles.

Question 7

Iron(III) nitrate and potassium thiocyanate equilibrium

Answer 7

3KSCN(aq) + Fe(NO3 )3(aq) Fe(SCN)3(aq) + 3KNO3(aq)

Question 8

What is a homogenous reaction?

Answer 8

A reaction where all the products are in the same phase.

Question 9

Dissolution

Answer 9

The process during which an ionic compound in water breaks up and its ions are dispersed throughout the water forming a solution.

Question 10

Dissociation

Answer 10

The breaking up of a compound into simpler constituents that are usually capable of recombining under other conditions.

Question 11

What is collision theory?

Answer 11

Collision theory is based on the assumption that, in order for a reaction to occur, reacting substances must collide, that they must collide with enough energy and that they must collide with the correct orientation.

Question 12

What is activation energy?

Answer 12

Activation energy is the minimum energy required for the reactants to overcome in order for the reaction to reach completion.

Question 13

Why is burning magnesium an irreversible reaction?

Answer 13

Changing conditions e.g temperature will not convert MgO back to its original products.

Question 14

How does activation energy affect the position of equilibrium?

Answer 14

Equilibrium reactions with smaller activation energies will reach the state of chemical equilibrium in less time than reactions requiring higher activation energies.

Lower activation energy means that the minimum collision energy required has been lowered. This means that the number of reactants (or products as dynamic equilibrium is two way reaction) that satisfy the minimum collision energy required as per collision theory has been increased.

Therefore the rate of successful collision reactions have been increased which equates to an increase in the rate of reaction.

If you increase the rate of reaction, the state of equilibrium can be attained with less time.

Question 15

How does the heat of reaction affect the position of equilibrium?

Answer 15

If there is a temp increase, reaction shifts to favour endothermic to consume added heat. If there is a temp decrease, reaction shifts to favour exothermic to produce more heat to counteract and minimise the drop in temperature.

Question 16

What is Ksp?

Answer 16

Ksp is the degree to which a compound dissociates in water. ˄ Ksp = more soluble compound.

Question 17

What is a saturated solution?

Answer 17

A saturated solution is a solution that will dissolve no more.

Question 18

How has solubility equilibria been used by Aboriginal and Torres Strait Islander Peoples to remove toxicity from foods?

Answer 18

Cycads contain (toxin) that is moderately soluble. 56.6 g/L. It is leached out by being ground up in running water over a long period of time. The running water will never reach 56.6 g/L because it is continuously flowing, so the toxin is able to be completely leached out.

Question 19

Burning Magnesium

Answer 19

2Mg + O2 → 2MgO

irreversible

Question 20

Burning steel wool

Answer 20

4Fe + 3O2 → 2Fe2O3

irreversible

Question 21

Analyse the effect of Combustion on entropy and enthalpy.

Answer 21

For e.g Octane
C8H18(l) + 25/2O2(g) –> CO2(g) +H2O(g)
ΔH < 0 (for all combustion rxns- as there is more energy in the bonds of reactants than products)
ΔS > 0 (more disorder)

Question 22

What is the relationship between collision theory and reaction rate in chemical equilibrium reactions?

Answer 22

The rate of reaction is the rate that particles collide with enough energy and correct orientation to create an activation complex, essentially it is the rate that all the aspects of collision theory occur. In equilibrium rxns, due to LCP, the methods of changing a ROR will affect the position of equilibrium.

Question 23

Effects of temp on heating cobalt(II) chloride hydrate reaction. Explain observations in terms of collision theory.

Answer 23

endothermic fwds rxn
Co(H2O)(aq) + 4Cl-(aq) ⇌ CoCl4 2-(aq) + 6H2O(l)
Pink colourless blue
- Heat: H2O(l) –> H2O(g), therefore ⇌ shifts right to replace H2O(l), therefore goes to blue.
- ΔH: ^ temp by heating causes ⇌ to favour fwd rxn bc it is endothermic.
- ^ temp is increasing rate of reaction as collisions have more energy.

Question 24

Effects of concentration on Iron(III) thiocyanate. Explain observations in terms of collision theory.

Answer 24

Fe3+(aq) + SCN-(aq) ⇌ [FeSCN]2+
Yellow colourless blood-red
- ^ conc causes shift to opposite side
- v conc causes shift to its side to replace
- More collisions in one direction of the equilibrium, therefore as shift occurs.

Question 25

What is Keq?

Answer 25

The equilibrium constant.
aA + bB ⇌ cC + dD

Keq = [C]^c x [D]^d / [A]^a x [B]^b

The value of Keq is only affected by changes in temp.

Question 26

What is the effect of temp on Keq?

Answer 26

The value of Keq is only affected by changes in temp.
For exothermic reactions, energy is released, therefore:
^ temp, reaction < , Keq decrease

For endothermic reactions, energy is required, therefore:
^ temp, reaction >, Keq ^
v temp, reaction

Question 27

Keq of iron(III) thiocyanate equilibrium.

Answer 27

3KSCN(aq) + Fe(NO3 )3(aq) Fe(SCN)3(aq) + 3KNO3(aq)

Keq = [Fe(SCN)3] x [KNO3]^3 / [KSCN]^3 x [Fe(NO3 )3]

Question 28

Dissolution

Answer 28

When an ionic compound is placed in water and its ions are dispersed throughout the water forming a solution.

Question 29

Describe the process of dissolution.

Answer 29

Ions are pulled away from the solid crystal lattice by the electrostatic charge / ion-dipole attraction between the water and the ions.
This creates a water ligand as they form complexes around the ions, preventing them from reforming the crystal lattice.
Aquo-cations and aquo-anions are formed.
When no more are able to be formed and the dissolution enters dynamic equilibria, the solution is said to be saturated.

Question 30

What does solubility depend on?

Answer 30

• the ability to attract / separate ions from the lattice (strength of the ionic bonding vs. the ion-dipole interactions).
– This is an endothermic process.
• the ability to form hydrated ions (strength of the ion-dipole interaction).
– This is an exothermic process.

Question 31

Potassium chloride and silver nitrate

Answer 31

KCl(aq) + AgNO3(aq) –> KNO3(aq) + AgCl(s)

Question 32

Potassium iodide and lead nitrate

Answer 32

2KI(aq) + Pb(NO3)2(aq) –> 2KNO3(aq) + PbI2(s)

Question 33

Sodium sulfate and barium nitrate

Answer 33

Na2SO4(aq) + Ba(NO3)2(aq) –> 2NaNO3(aq) + BaSO4(s)

Question 34

What is Ksp?

Answer 34

• The solubility constant - Ksp value indicates the degree to which a compound dissociates in water.
• The higher the solubility product constant, the more soluble the compound.