Oceans Flashcards
What are the two types of solvent?
Polar and non Polar
Why do ionic substances only dissolve in polar solvents?
The ion-dipole bonds formed are stronger than the electrostatic forces between the ions
Why don’t ionic substances dissolve in non-polar solvents?
Non polar molecules don’t interact strongly enough with the ions
Why do covalent substances dissolve in non-polar solvents?
Intermolecular bonds between covalent molecules are weak and can be broken by non polar solvents
Why don’t covalent molecules tend to dissolve in polar solvents?
Hydrogen bonds between water molecules are stronger than bonds between covalent molecules and the water.
How do ionic solids dissolve in water?
1) partially positive charge on H attracted to negative ions
2) partially negative charge on O attracted to positive ions
3) Ions separate from ionic lattice and becomes surrounded by water molecules
What is Hydration?
When a molecule becomes surrounded by water molecules
What is an ion called when it is surrounded by water molecules?
Hydrated ion
What is hydration called when the solvent isn’t water?
Solvation
What is the definition of standard lattice enthalpy?
the enthalpy change when `1 mole of an ionic lattice is formed from its gaseous ions under standard conditions
What is a giant ionic lattice?
Positive and negative ions held together by electrostatic attractions in a lattice (formed by ionic compounds)
What charge is lattice enthalpy?
Always negative because bonds and broken and energy is released
What makes standard lattice enthalpy more negative?
It is a measure of bond strength so the stronger the bonding the more negative it is
What is the definition of enthalpy change of hydration?
The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions.
Is enthalpy change of hydration endothermic or exothermic?
exothermic
What is the definition of enthalpy change of solution?
Enthalpy change 1 mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution
What is the overall effect on enthalpy when something dissolves called?
enthalpy change of solution
How do you measure enthalpy change of solution using an experiment?
Put reactants in polystyrene and measure temp change
What equation do you use to calculate enthalpy change?
q=mc x change in temp
What is charge density?
charge/radius
How is lattice enthalpy affected by charge density?
Ions with higher charge density are better at attracting each other in ionic lattices - so it has a more exothermic lattice enthalpy because the ionic bonds are stronger
How does charge density affect enthalpy of hydration?
Ions with higher charge molecules are better at attracting water molecules than those with lower charge densities - so it would have a more exothermic enthalpy of hydration
What is solubility?
The maximum amount of solid which will dissolve in a certain solvent
Equation for moles using mass
moles = mass/mr
What is Ksp
solubility product
What is entropy?
Number of ways that particles can be arranged and the number of ways that the energy can be shared between the particles.
Does increased disorder increase or decrease energetic stability of a substance?
Increase
Put the states in order of increasing enthalpy
solid, liquid, gas
Why do gases have the highest disorder?
most random arrangement of particles
What is energy measured in?
quanta - packages of energy
How does energy affect entropy?
Increased energy quanta means more ways particles can be arranged and the greater entropy
How does the moles affect entropy?
More moles means more particles so more ways the particles can be arranged
What is the equation for total entropy change?
ΔtotS = ΔsysS + ΔsurrS
What is the equation for entropy of the system?
ΔsysS = Sproducts - S reactants
What is the equation for entropy of the surroundings?
ΔsurrS = -ΔH/T
ΔH in Jmol-1
T in K
What does the total entropy change need to be for reactions to be feasible?
Positive or zero
If the ΔsysS is negative what should ΔsurrS be to make the reaction feasible?
positive and at least as large as ΔsysS
What factors affect entropy?
- moles
- physical states
- temperature
