Thermodynamics Flashcards
Define enthalpy change
Heat energy transferred in a reaction at constant pressure
Define enthalpy change of formation
Enthalpy change when 1 mole of a compound is formed from its elements under standard states under standard conditions
Define bond dissociation enthalpy
Enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules are broken
Define enthalpy change of atomisation of an element
Enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Define enthalpy change of atomisation of a compound
Enthalpy change when 1 mole of a compound is converted to gaseous atoms under standard states
Define first ionisation energy
Enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms
Define second ionisation energy
Enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of 1+ gaseous atoms
Define electron affinity
Enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms
Define second electron affinity
Enthalpy change when 1 mole of gaseous 2- ions is formed from 1 mole of 1- gaseous atoms
Define enthalpy change of hydration
Enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions
Define enthalpy change of solution
Enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on furthur dilution
Define lattice enthalpy of formation
Enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard conditions
Define lattice enthalpy of dissociation
Enthalpy change when 1 mole of solid ionic compound is completely dissociated into its gaseous ions under standard conditions
What does the purely ionic lattice assume?
- All ions are spherical
- Evenly distributed charge
- No covelant character
What does it mean when the difference btw experimental + theoretical lattice enthalpy are big?
- Bonding is stronger than ionic model predicts
- Bonds are strongly polarised + have a lot of covelant character
What does it mean when the difference btw experimental + theoretical lattice enthalpy are small?
Close to being purely ionic
When a solid ionic lattice dissolves in water, what are the 2 things that happen?
- Bonds btw ions break to give free ions - endo
- Bonds btw ions + water are made - exo
When can substances only dissolve?
If energy released is roughly the same, or greater than the energy taken in
Define entropy
Measure of the no. ways that particles can be arranged + no. ways that energy can be shared out btw the particles
Large positive entropy
High level of disorder
What affects entropy?
- Physical state - gas has highest entropy
- No. particles - more particles = entropy inc
Why do particles move to increase their entropy?
More energetically stable when theres more disorder
For a reaction to be feasible it must be..
-ve
