How do polar substances dissolve in polar solvents?
-Some, like water, hydrogen bond (aqueous solution)
-Some, like propanone, have permanent dipole- dipole interactions and instantaneous- induced dipole forces (non- aqueous solutions)
How do ionic compounds dissolve in polar solvents like H2O?
- the delta + charge on the H bond to -ve charges. The delta - on the O bond to +ve charges, so structure starts to break down.
What is required for an ionic compounds dissolve to dissolve in polar substances like H2O?
- new bonds formed must be the same strength or greater than the bonds broken
- if not substance is unlikely to dissolve.
Al2O3 doesn’t dissolve as the ionic bonding to too strong.
Why can alcohols dissolve in water?
The -OH can hydrogen bond with the water molecules
The hydrocarbon chain is non-polar so doesn’t dissolve in water, the larger the hydrocarbon chain, the less soluble the alcohol
Why don’t haloalkanes dissolve in water?
- Weak bonds
- water forms stronger bonds with other water molecules than with the haloalkane so haloalkanes are insoluble.
What van haloalkanes dissolve in?
They can dissolve in solutions that interact via permanent dipole- permanent dipole interactions
What do non-polar substances dissolve best in?
- They dissolve best in non-polar solvents.
- non-polar solvents only have instantaneous- induced dipole forces between molecules
Why don’t non-polar substances dissolve in water?
Water forms stronger hydrogen bonds itch other water molecules than interaction with non-polar molecules
What assumptions are made when calculating enthalphy change of solution?
- Break down the solid lattice into gaseous ions first
- Then dissolve the gaseous ions in water
What is included in an energy level diagram?
- lattice enthalpy
- enthalpy change of solution
- enthalpy of hydration
What is the equation of enthalpy of hydration?
Enthalpy of hydration = lattice enthalpy change + enthalpy change of solution
What is entropy?
A measure of disorder in a system.
The number of ways energy can be shared out between particles
Order the entropy from lowest to highest for:
Solid, liquid, gas
Solid, liquid, gas
What affects entropy?
- the number of particles
- the amount off energy a substance has
How does the number of particles affect entropy?
If a reaction is in the same state, but more moles are produced, entropy increases
E.g. N2O4 -> 2NO2
What is the equation for the change of entropy in a system?
Change in entropy system = entropy of products - entropy of reactants
What are the units for entropy (s)?
JK-1mol-1
What is the equation for total entropy change?
Total entropy change = change in entropy of system + change in entropy of surrounding
What is the equation for change in entropy of surroundings?
-change in enthalpy (J mol-1) / temperature (K)
What is a feasible reaction?
Is where a reaction will carry on to completion without any energy being provided to it.
The entropy > 0
What is solubility?
The extent to which solid dissolves in solution
It is effected by the type of solid, temperature and pressure.
What is the point of saturation?
The point at which the water can no longer hold any more solid. Additional solid added will no longer dissolve
What are the units for solubility?
g dm-3
And temperature dependent, so temp will be quoted
