Lattice enthalpy Flashcards
Define lattic enthalpy
Lattice enthalpy is a measure of the strength of ionic bonding in a giant covalent lattice.
Lattice enthalpy is the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
Define standard enthalpy change of formation
The enthalpy change that occurs when one mole of a coumpound is formed from its constituent elements, under standard conditions with all reactants and products in their standard states.
Define the standard enthalpy change of atomisation
The enthalpy change that occurs to form one mole of gaseous atoms from its element(s) in their standard state under standard conditions.
Define first ionisation energy
The enthalpy change that occurs when one mole of electrons are removed from one mole of gaseous ions to from one mole of gaseous 1+ ions.
Define first electron affinity
The enthalpy change that occurs when one electron is added each atom in one mole of gaseous atoms to form one mole of 1- gaseous ions.
Define enthalpy change of solution
Enthalpy change of solution is the enthalpy change that occurs when one mole of a solute dissolves in a solvent.
(To form one mole of aqueous ions)
Define enthalpy change of hydration
Enthalpy change of hydration is the enthalpy change that occurs when dissolving one mole of gaseous ions in water to form one mole of aqueous ion.
How does ionic size affect the lattice enthalpy?
As the ionic radius increases, the attraction between ions decreases. Leading to a less negative lattice energy/enthalpy, and lower melting points.
What two factors affect lattice enthalpy and enthalpy of hydration, just list.
Ionic size (ionic radius)
Ionic charge
How does ionic charge affect lattice energy
As ionic charge increases, the attraction between ions increases. Leading to a more negative lattice energy/enthalpy, and higher melting points.
How does ionic size affect enthalpy of hydration?
As the radius of ions increase, the attraction between the ions and water decreases leading to a less negative hydration enthalpy/energy.
How does ionic charge affect the enthalpy of hydration?
As the charge of ions increases, the attraction between the ions and water molecules also increases, leading to a more negative hydration enthalpy/energy.
Describe entropy
Entropy is a measure of the dispersal of energy in a system, which is greater the more disordered a system.
What happens to energy an entropy as a system becomes more random?
Energy is spread out further leading to a higher entropy value, positive ΔS.
What will happen to the energy and entropy of a system as it becomes less random?
Energy will become less spread out and entropy will decrease, negative ΔS.
Define standard entropy
Standard entropy in the entropy of one mole of a subsatance under standard conditions (100 KPa and 298 K).
If a subsatance were to change state from a solid to a liquid to a gas what would the enthalpy change be and why?
Enthalpy change ΔS would be positive as melting and boiling increase the randomness of the particles, spreading out energy further leading to a positive ΔS.
Write the gibbs free energy equation
ΔG = ΔH- TΔS
In the gibbs free energy equation what is ΔH?
Enthalpy change, heat transfered between the system and the surroundings
In the Gibbs energy equation what is ΔG and what must it’s value be for the reaction to be feasible?
ΔG = Free energy
ΔG must be negative ( there must be a decrease in free energy for a reaction to be feasible).
In the gibbs free energy equation what is TΔS
T = Temperature
ΔS = Entropy change
What is the limitations of the Gibbs free energy?
The gibbs free energy equation does not account for the kinetics or rate of reaction for an equation.
For example a reaction may have a negative ΔG but not take place due to the large activation energy needed.
What is used to test for cations?
Aqeous sodium hydroxide
What is formed when a copper ion reacts with aqueous sodium hydroxide?
A blue precipitate
What is formed when Iron 2+ and 3+ ions react with aqueous sodium hydroxide?
Fe 2+ = green precipitate
Fe 3+ = brown precipitate
What is formed when manganese ions 2+ react with aqeous soidum hydroxide?
a light brown precipitate
How can a substance be tested to contain ammonium ions?
On the addition of aqueous sodium hydroxide ammonia gass will be produced, which turns damp red litmus paper blue.
What is formed when chromium ions 3+ react with aqeous sodium hydroxide?
A green solution.
