O 1 - Energetics Flashcards
What are the factors determining the relative solubility of a solute in aqueous and non-aqueous solvents?
Temperature, polarity (i.e. ionic bonds, intermolecular bonds etc.), molecular size
What are hydrated ions?
An ion surrounded by water molecules in a spherical-shaped shell
What is enthalpy change of solution?
The enthalpy change that occurs when one mole of ionic solid dissolves in water to form one mole of aqueous ions, under standard conditions
What is lattice enthalpy?
The enthalpy change when one mole of an ionic compound is formed from its gaseous ions, under standard conditions
(exothermic)
What is the enthalpy change of hydration of ions?
The enthalpy change when one mole of gaseous ions are completely hydrated by water to form one moles of aqueous ions, under standard conditions
What is charge density?
The charge per unit volume/surface area/length
How are lattice enthalpy and enthalpy change of hydration affected by charge density of the ions?
The greater the charge density of the ions:
- The more exothermic the lattice enthalpy due to increased electrostatic attraction
- The more exothermic the hydration enthalpy due to increased attraction of water molecules
What is entropy?
It measures the number of ways that molecules can be arranged; quite simply it is the measure of disorder in a system
How can you predict whether entropy change is positive or negative?
- Entropy increases from a solid to a liquid/aqueous to a gas. E.g. if a reaction causes a liquid and a solid to form a gas, then the entropy change is positive
- If there are more gaseous prod7ucts that reactants then entropy will increase and hence the change will be positive
What is the total entropy change equal to?
^(total)S = ^(sys)S + ^(surr)S
(total entropy change = entropy change of the system + entropy change of the surroundings)
What is the entropy change of the surroundings equal to?
^(surr)S = (-^H) / (T)
where ^H is the enthalpy change of the reaction and T is the temperature in Kelvin
When is a reaction feasible?
When the told entropy change, ^(tot)S is positive
How do you calculate the entropy change of the system (given the entropies of reactants and products)?
^(sys)S = ^S(products) - ^S(reactants)
What is solubility product?
- The solubility product constant, Ksp, is an equilibrium constant for a solid dissolving in (aqueous) solution
- The higher its Ksp, the more soluble a substance is hence the more solute that dissolves
How do you calculate Ksp?
For reaction: aA(s) <=> cC(aq) + dD(aq)
Ksp = [C]^c[D]^d
Solids are not included as their concentrations don’t affect the expression and are hence insignificant
