lattice enthalpy + energy + entropy Flashcards
lattice enthalpy definition
the amount of energy released when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions
- it is always exothermic (-) as ionic lattice is lower in energy than the ions that formed it, so energy is released from ions as lattice forms
standard enthalpy of atomisation definition
the enthalpy change that occurs when 1 mole of gaseous atoms is formed from an element in its standard state under standard conditions
- it is always endothermic (+) as energy is required to break bonds holding atoms together in a molecule e.g. Cl2, O2
first ionisation energy definition + example equation
the enthalpy change required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
e.g. X(g)»_space; X+(g) + e-
first electron affinity definition
the enthalpy change that occurs when 1 electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions
why might second electron affinity be endothermic even if first electron affinity is exothermic
when adding the second electron, it may experience repulsive forces from the first electron that was added, which means more energy is required to add the electron, so overall enthalpy change is + (endo)
enthalpy change of hydration definition
the enthalpy change that occurs when 1 mole of a gaseous ion is completely hydrated by water under standard conditions
- it is usually exothermic (-) as bonds/forces of attractions are formed between ions and water molecules, which releases energy
enthalpy change of solution definition
the enthalpy change that occurs when 1 mole of an ionic solid is dissolved in water/a solvent under standard conditions
what are standard conditions
298 K and 100 kPa
what factors affect lattice enthalpy + how
ionic size - as atomic radius increases, charge density decreases so attraction between ions decreases - as a result lattice enthalpy becomes less negative/exo
ionic charge - as ionic charge increases, attraction between ions increases and lattice enthalpy gets more negative/exo
entropy (S) definition + units
entropy is a measure of dispersal of energy within a system, based on the disorder of a system
units = J K-1 mol-1
describe how entropy changes from a
solid > liquid > gas
solids have very low entropy as particles are arranged regularly
liquids have higher entropy as particles are more free to more around each other so there is a greater level of disorder
gases have the greatest entropy as particles are free to move around and are far apart so high level of disorder and dispersal of energy
how does entropy change in a reaction that goes from 1 liquid mole»_space; 1 gas mole
entropy increases, as 1 gas mole has a greater entropy than 1 liquid mole
how does entropy change in a reaction that goes from 3 gas moles»_space; 1 gas mole
entropy decreases, as 3 gas moles have a greater entropy than 1 gas mole
standard entropy definiton + where to find it
the entropy (dispersal of energy) of 1 mole of a substance under standard conditions
these values can be found in databases
feasibility definition
a reaction is feasible if the products have less free energy than the reactants, making ΔG negative (<0)
