Chemical energetics Flashcards
Define lattice energy.
Lattice energy is the enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard conditions.
Define first electron affinity.
The first electron affinity is the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous 1‐ ions under standard conditions.
What are the factors affecting the value of electron affinity?
Nuclear charge
Atomic size
Shielding effects
What are the factors affecting value of lattice energy?
Size of the ions
Charge of the ions
What is ion polarization?
It occurs when a cation attract electrons and distort an anion.
What are the conditions for ion polarization?
Cation must be small with a 2+ or 3+ charge.
Anion must be large with a 2- or 3- charge.
Explain the thermal stability of group 2 carbonates and nitrates.
Carbonate and nitrates are large anions.
Going down the group 2, ionic radius of cation increases whereas ionic charge remains the same.
Charge density decreases.
Ion polarization decreases.
The compounds are more thermally stable.
Define enthalpy change of solution.
The enthalpy change when 1 mole of substance dissolves in water to form a very dilute solution under standard conditions.
Define enthalpy change of hydration.
The enthalpy change when 1 mole of a gaseous ion dissolves in water to form a very dilute solution under standard conditions.
Describe the factors affecting enthalpy change of hydration.
Ionic radius.
The smaller the ionic radius, the greater the charge density.
Stronger ion-dipole interactions with water increases.
Enthalpy change more exothermic.
Ionic charge.
The greater the ionic charge, the stronger the ion-dipole interactions with water. Enthalpy change more exothermic.
Define entropy.
The measure of disorder of a system.
What are the factors that affect entropy?
Number of molecules
Physical state of compound
Describe the trend in the solubility of metal hydroxides going down Group 2.
Less soluble to more soluble.
Hlatt and Hhyd both becomes less exothermic.
Hlatt changes more.
Hsol becomes more exothermic.
Describe the trend of solubility of sulfates going down Group 2.
More soluble to less soluble.
Hlatt and Hhyd both becomes less exothermic.
Hlatt changes less.
Hsol becomes less exothermic.
