U1S6- Thermodynamics Flashcards
Define enthalpy change.
The heat energy transferred in a reaction at constant pressure.
Define the term exothermic reaction.
Heat energy is given out. Negative delta H value.
Define the term endothermic reaction.
Heat energy is absorbed. Delta H is positive.
Define enthalpy change of formation.
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
Define enthalpy change of atomisation of an element.
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.
Define bond dissociation enthalpy.
The enthalpy change when all the bonds of the same type in 1 mole of gaseous molecules is broken.
Define the enthalpy change of atomisation of a compound.
The enthalpy change when 1 mole of a compound in its standard state is converted into gaseous atoms.
Define first ionisation energy.
The enthalpy change when 1 mole of gaseous 1+ ions are formed from 1 mole of gaseous atoms.
Define second ionisation energy.
The enthalpy change when 1 mole of gaseous 2+ ions are formed from 1 mole of gaseous 1+ ions.
Define first electron affinity.
The enthalpy change when 1 mole of gaseous 1- ions are formed from 1 mole of gaseous atoms.
Define second electron affinity.
The enthalpy change when 1 mole of gaseous 2- ions are formed from 1 mole of gaseous 1- ions.
Define enthalpy change of hydration.
The enthalpy change when 1 mole of aqueous ions are formed from 1 mole of gaseous ions.
Define enthalpy of solution.
The enthalpy change when 1 mole of solute is dissolved in enough solvent that no further enthalpy change occurs on further dilution.
Define lattice enthalpy of formation.
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions.
Define lattice enthalpy of dissociation.
The enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions.
State Hess’s law.
The total enthalpy change of a reaction is always the dame, no matter which route is taken.
What is the theoretical lattice enthalpy based on?
Purely ionic model.
What 2 things does the purely ionic model assume?
That all the ions are spherical.
Their charges are evenly distributed around them.
Define covalent character.
The bonds are strongly polarised and the difference between the experimental and theoretical values are bigger.
What 2 things happen when a solid ionic lattice dissolves in water?
. Bonds between ions break to give free ions-endothermic.
. Bonds between the ions and water are formed-exothermic.
Why can the water molecules bond to the ions? (4 stages)
. O more electronegative than H.
. So draws electrons to itself which creates a dipole.
. + H atoms form bonds with - ions.
. - O atoms form bonds with + ions.
When do substances generally only dissolve?
. Energy released is greater than or equal to energy taken in.
. Therefore, exothermic.
Draw a Born Haber cycle and work out enthalpy change of solution for NaCl.
Enthalpy of hydration of Na+(g)=-406
Enthalpy of hydration of Cl-(g)=-364
Lattice dissociation enthalpy=+787
+17 kJmol^-1
Define entropy (3 things)
A measure of the number of ways that the particles can be arranged.
A measure of the number of ways energy can be shared out.
The more disordered the particles are, the higher the entropy.
State 2 things that affect entropy?
. Physical state.
. More particles.
When are particles more energetically stable?
When there is more disorder, so they tend towards disorder.
When are some reactions more feasible?
An increase in entropy in a reaction means that that reaction is feasible.
Define standard entropy.
The entropy of 1 mole of that substance under standard conditions.
