MODULE 5 Flashcards
What are reversible reactions?
Reactions in which formed products can react with each other to reform reactants. E.g. Haber Process.
What is REVERSIBILITY CASE STUDY 1? (Include chemical formula in answer)
Cobalt (II) Chloride Hydrated (CoCl2 * 6H20 (s)) and Dehydrated (CoCl2 (s))
REVERSIBILITY CASE STUDY 1:
Cobalt (II) Chloride Hydrated and Dehydrated
1) What happens when it is heated?
2) What happens when deionised water is added?
1) Heating CoCl2 * 6H20 (s) causes its colour to change from pink to sky blue CoCl2 (s). It no longer contains water.
2) Adding deionised water back to CoCl2 (s) causes its colour to change from sky blue to pink CoCl2 * 6H20 (s).
Note that adding too much water may result in it turning from (s) into (aq).
1) What is REVERSIBILITY CASE STUDY 2? (Include chemical formula in answer)
2) What is its net ionic equation?
Include ΔH for both.
1) Iron (III) Nitrate and Potassium Thiocyanate:
Fe(NO3)3 (aq) + KSCN (aq) <=> FeSCN2+ (aq) + KNO3 (aq) ΔH <0
2) Fe3+ (aq) +SCN- (aq) <=> FeSCN2+ (aq) ΔH <0
REVERSIBILITY CASE STUDY 2:
Iron (III) Nitrate and Potassium Thiocyanate
1) Is this a static or dynamic equilibrium? Why?
2) Does it reach completion?
3) What would its visual appearance be?
1) This reaction is a true dynamic equilibrium as the reactants form products and the products form reactants simultaneously. At sone point, the rates of forward and reverse reaction will become equal but not zero.
2) This reaction will never go to 100% completion and there will always be some reactant and some product at the same time.
3) It would have a mix of pale-orange (Fe3+), colourless (SCN-), and blood-red (FeSCN2+) since all three substances are always present.
What is equilibrium?
A state in which the concentrations of reactants and products are constant and the rates of forward and reverse reaction are equal.
System vs Surrounding vs Universe
A system is a chemical reaction, including all matter and energy (this does not include the beaker).
The surroundings are everything else in existence that are not part of the system (including the beaker and air).
Universe = System + Surroundings
Closed vs Open vs Isolated Systems
A closed system contains a constant number of particles however energy can be exchanged with the surroundings.
(No matter transferred, only energy)
Static and dynamic equilibria both require closed systems*?
An open system can interact with surroundings allowing exchange of BOTH matter and energy.
Isolated systems permit neither matter nor energy to transfer between system and surroundings.
Dynamic vs Static Equilibrium
1) Definitions
2) Macroscopic (concentrations)
3) Microscopic (reaction rate)
4) Reaches completion?
5) Reversibility
6) Example
1) A dynamic equilibrium is a steady state in which the concentrations of reactants and products are constant and the rates of forward and reverse reaction are equal and non-zero.
A static equilibrium is a static state in which concentrations of reactants and products are constant and rates of forward and reverse reaction are equal and zero (or almost zero, but we usually do not mention this).
2) In both dynamic and static equilibrium, concentrations are constant.
3) In dynamic, there is an in flux (non-zero) rate of reaction while in static, there is an constant zero rate of reaction.
4) Dynamic never reaches completion. Static reaches completion.
5) Dynamic is reversible. Static is non-reversible.
6) Example of dynamic equilibrium is Haber Process:
N2 (g) + 3H2 (g) <=> 2NH3 (g).
Example of static equilibrium is the formation of graphite into diamond:
C (graphite) => C (diamond)
This process is so slow (takes 1000s of years) that the ROR is basically zero.
What is Enthalpy (H)?
Internal enemy of a system. It is used interchangeably with heat in chemistry.
What are the units for enthalpy (H)?
Enthalpy is measured in J/mol or kJ/mol.
Only CHANGE in Enthalpy can be measured, absolute Enthalpy cannot be measured!
One way to calculate ΔH is…
ΔH = ΣH° (products) - ΣH° (reactants)
What is standard Enthalpy of formation (ΔH°f)?
It is the change in enthalpy associated with the formation of 1mol of a substance in its standard state from its constituent elements in their standard states.
Standard state is at 25°C and 100kPa
Note: The standard formation of an element at its standard state is 0kJ/mol.
Describe Enthalpy Drive and Movement of Energy for exothermic (ΔH < 0) and endothermic (ΔH > 0) reactions.
In an exothermic (ΔH < 0) reaction, there is a forward enthalpy drive and energy is released into surroundings.
In an endothermic (ΔH > 0) reaction, there is a reverse enthalpy drive and energy is absorbed from the surroundings.
What is Entropy (S)?
The number of possible microscopic configurations of a system. a.k.a. How disordered the chemical system is.
What are the units for entropy (S)?
Absolute entropy can be measured in J/mol/K or kJ/mol/K.
Absolute entropy CAN be measured and is always positive.
What four factors impact entropy (S)?
- Concentration
- Temperature
- State
- Pressure/Volume
Describe the entropy drive and state of disorder for when entropy increases (ΔS > 0) and when it decreases (ΔS < 0).
When entropy increases (ΔS > 0), there is a forward entropy drive and disorder increases.
When entropy decreases (ΔS < 0), there is a reverse entropy drive and disorder decreases.
What is the Zeroth Law of Thermodynamics?
If two systems are in thermal equilibrium with a third system, then they are all in thermal equilibrium with each other.
What is the First Law of Thermodynamics?
Energy movement into or out of a system is in accordance with the Law of Conservation of Energy.
What is the Second Law of Thermodynamics?
The entropy of an isolated system not at equilibrium will increase over time, approaching a maximum value at equilibrium.
Another interpretation: The entropy of the universe must be increasing.
ΔS (universe) = ΔS (system) + ΔS (surroundings) > 0
What is the Third Law of Thermodynamics?
The entropy of a system approaches a minimum as temperature approaches zero.
What is Gibbs Free Energy?
Free Energy: Energy that is required to do work.
What is Gibbs Free Energy?
Free Energy: Energy that is required to do work.
