Solutions, Solubility and Thermodynamics Flashcards
Solution
A homogeneous mixture containing particles the size of a typical ion or covalent molecule. (0.1–2.0 nm in diameter)
Colloid
A homogeneous mixture containing particles with diameters in the range 2–500 nm
Suspensions
Mixtures with even larger particles, but they are not considered true solutions because they separate upon standing
Solute
The dissolved substance in a solution
Solvent
The major component in a solution
Solubility
The maximum amount of solute that can dissolve in a specific amount of solvent usually 100 g.
g of solute / 100 g water
A solution is saturated when…
…no additional solute can be dissolved at a particular temperature
A Supersaturated solution can form when…
…more than the equilibrium amount of solute is dissolved at an elevated temperature, and then the supersaturated solution is slowly cooled.
An Unsaturated solution is formed when…
more of the solute can dissolve in it at a particular temperature.
What is the condition for crystallisation?
For crystallisation to occur, the molecules or ions of solute must arrange themselves properly to form crystals.
Factors affecting solubility…
Solute-solvent interaction Temperature effect (Solid and Liquid) Pressure effect (Gases)
What is the relationship between the solubility of gases and their sizes?
Solubility of gases increases with size of gas due to London dispersion force
Temperature and Solubility of Solids
The solubility of most solids increases with an increase in the temperature
Temperature and Solubility of Gases
The solubility of gases decreases with an increase in temperature.
Relationship between solubility and pressure
Pressure has little effect on the solubility of liquids and solids. The solubility of gases is strongly influenced by pressure. Gases dissolve more at high pressure.
What does Henry’s law show?
The relationship b/w pressure and the solubility of a gas
According to Henry’s law, what does the solubility of a gas in a liquid depend on?
Temperature
The partial pressure of the gas over the liquid,
The nature of the solvent,
The nature of the gas.
State Henry’s law
At constant temperature the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas in equilibrium
Cg= khPg
What are the conditions for Henry’s law?
Molecules are at equilibrium.
Gases not at high pressures (e.g., N2(g) asupply)
No chemical reaction between the solute and solvent
When do deviations from Henry’s law become noticeable?
As concentrations and partial pressures increase, deviations from Henry’s law become noticeable.
What are solutions which are found to obey Henry’s law called?
Ideal dilute solutions
How does antifreeze work?
The added solute also raises the boiling point of the solution above that of pure water, making it possible to operate the engine at a higher temperature.
What are colligative properties?
Colligative properties are physical properties of solutions that depend on the quantity (concentration) but not the kind or identity of the solute particles. Colligative properties depend on the collective effect of the number of solute particles.
Examples of colligative properties
Freezing-point depression
Boiling-point elevation
Vapor-pressure lowering
Osmotic pressure
What is vapour pressure?
The vapour pressure is the pressure exerted by the vapor when it is at equilibrium with the liquid (that is, when the rate of vaporization equals the rate of condensation).
How does vapour pressure determine volatility?
A substance that has no measurable vapor pressure is nonvolatile, whereas one that exhibits a vapor pressure is volatile.
Describe the formation of a solution of volatile and non-volatile components.
A solution consisting of a volatile liquid solvent and a nonvolatile solute forms spontaneously because of the increase in entropy that accompanies their mixing.
Therefore, when a nonvolatile solute is present, the vapor pressure of the solvent is lower than the vapor pressure of the pure solvent,
State Raoult’s law
It states that the partial vapor pressure exerted by solvent vapor above the solution, Psolution, equals the product of the mole fraction of the solvent, Xsolvent, times the vapor pressure of the pure solvent, P°solvent:
Psolution = Xsolvent . P°solvent
What are the conditions for Raoult’s law?
Raoult’s law assumes that the solution is ideal. Therefore, the forces between solute and solvent molecules must be the same as the solvent to solvent.
What is an ideal mixture?
An ideal mixture of two liquids will have zero enthalpy change of mixing.
What is boiling point elevation?
If you add solute it will change the solvent’s vapor pressure, therefore the boiling point changes.
The Boiling point elevation, ΔTb, is directly proportional to the molality of the solution
ΔTb= Kbmsolute
What happens with freezing point depression?
There are more atoms of pure solvent going from solid to liquid than from liquid to solid.
Examples of ideal mixtures
hexane and heptane
benzene and methylbenzene
propan-1-ol and propan-2-ol
What happens in a non-ideal solution?
Solute-solvent interactions are significantly different from solute-solute and solvent-solvent interactions
Negative deviation from Raoult’s law
- The vapor pressure of a mixture is lower than expected.
- The adhesive forces between different components are stronger than the average cohesive forces between like components
- Both components have a lower escaping tendency in the solution than in the pure liquids
- Liquids mix exothermically.
Positive deviation from Raoult’s law
- Two liquids mix endothermically, this indicates that the solute-solvent interactions are weaker than the interactions among the molecules in the pure liquids.
- The cohesive forces between like molecules are greater than the adhesive forces
- Dissimilarities of polarity leads both components to escape solution more easily.
- Vapor pressure is greater than expected from Raoult’s law.
Examples of positive deviation from Raoult’s law
benzene and methanol
carbon disulfide and acetone
chloroform and ethanol
Examples of negative deviation from Raoult’s law
chloroform and acetone
What is chemical thermodynamics?
The chemistry that deals with energy exchange, entropy, and the spontaneity of a chemical process.
Diathermal walls
The system and its surroundings are separated by walls of some kind. Walls that permit heat to flow through them, such as those of the engine block, are called diathermal walls.
Properties of internal energy
- The sum of all possible forms of energy in a system.
- Cannot be measured, we can only measure changes in energy
- Atoms, ions and molecules all possess internal energy
- Independent of pathways used to reach the state
State function
A property dependent only on the state of the system (i.e. what condition that system is in and not on the pathway)
Examples of state functions
Pressure
Temperature
If the products have more energy than the reactants …
…the change is positive
If the reactants have more energy than the products …
…the change is negative
What does Gibb’s free energy do?
G controls the position of equilibrium in closed systems at constant temperature and pressure
Applications of thermodynamics
Extraction, refining Corrosion Phase transformation-phase diagram calculation Materials processing Design of new materials.
Types of thermodynamics systems
Open
Closed
Isolated
Explain the term, phase.
The term, phase is used for that portion of the investigated system volume in which its proper ties are constant or continuously changing in space
When does a thermodynamic process take place in a system?
If the properties of a system change in time, i.e. if at least one thermodynamic quantity changes, we say that a certain thermodynamic process takes place in the system.
Types of thermodynamic processes
Reversible and Irreversible Processes
Processes at a constant quantity
Cyclic Processes
What is a reversible process?
If a system is nearly at equilibrium in every moment, and that, consequently, the direction of the process may be reversed by even a very slight change of the initial conditions, the process is called reversible or equilibrium. A reversible process is thus a sequence of (nearly) equilibrium states of a system.
What is an irreversible process?
A real world system is out of equilibrium at least at the beginning. These processes are called irreversible or non-equilibrium (the direction of the process cannot be reversed by any slight change of external conditions, and the process is a sequence of non-equilibrium states)
Isothermal
Temperature
Isobaric
Pressure
Isochoric
Volume
Adiabatic
Heat
Isentropic
Entropy
Isenthalpic
Enthalpy
Polytropic
Heat capacity
What is a cyclic process?
A cyclic process is such at which the final state of the system is identical with its initial state. In a cyclic process, changes of thermodynamic quantities are zero.
What is a property?
Any characteristic of a system in equilibrium is called a property.
- vary directly with the size of the system
Examples: volume, mass, total energy
- are independent of the size of the system
Examples: temperature, pressure, color
Types of properties
Extensive properties
Intensive properties
Extensive properties
Vary directly with the size of the system.
Examples: volume, mass, total energy
Intensive properties
Are independent of the size of the system
Examples: temperature, pressure, color
Extensive properties per unit mass are…
…intensive properties, eg. Specific volume v = Volume/Mass = V/m, Density r = Mass/Volume = m/V
Spontaneous Reaction-
-
A reaction that occurs under specific conditions, occurs without outside intervention.
Non-spontaneous Reaction
A reaction that does not occur under specific conditions
