Thermodynamics

enthalpy of formation

enthalpy of formation

the enthalpy change when one mole of a substance is formed from its constituent elements, in standard conditions with everything in standard states

ionisation energy

the ionisation energy of an element is the amount of energy required to remove an electron from a gaseous atom of an element to form a gaseous ion under standard conditions

enthalpy of atomisation

The standard enthalpy change of atomisation is the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions

bond enthalpy

The amount of energy required to break one mole of a covalent bond in the gas phase is called the bond dissociation energy

electron affinity

The electron affinity of an element is the energy change when one mole of electrons is gained by one mole of gaseous atoms of an element to form one mole of gaseous ions under standard conditions

lattice enthalpy

the enthalpy change when 1 mole of a ionic crystal is formed from the gaseous ions (at standard conditions)

enthalpy of hydration

The standard enthalpy change of hydration is the enthalpy change when 1 mole of a gaseous ion dissolves in sufficient water to form an infinitely dilute solution

enthalpy change

the amount of heat energy transferred during a chemical reaction, at a constant pressure

what do bon harber cycles allow us to calculate

lattice enthalpy for ionic compounds

endothermic arrows point

up, the energy increases

exothermic arrows point

down, the energy decreases

order of bon harber cycle (left to right)

elements in standard states

gaseous atoms

gaseous ions'

product in standard state

if theoretical and experimental enthalpys are the same then

compound is mainly ionic, only electrostatic attraction

if theoretical and experimental enthalpy’s are different then

compound will have some covalent elements

what is covalent character in ionic compounds

left to right across periodic table compounds become less ionic and more covalent in charcater

how covalent distortion happens

one ions has a stronger electrostatic attraction and pulls electrons towards itself, giving it some covalent character

what ion is good at dissorting

positive ions that are small/highly charged are very good at polarising negative ions

standard enthalpy of solution

the enthalpy change when 1 mole of an ionic substance dissolves in sufficient water to form an infinitely dilute solution

standard enthalpy of hydration

the enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form an infinitely dilute solution

enthalpy of solution=

reverse lattice enthalpy + hydration enthalpy

what is the symbol for entropy

s

what is entropy

measure of disorder, the more disorder the greater the entropy

what is the unit of entropy

J mol-1 K-1

what has greater entropy, solid or gas

gas has greater entropy as particle move rapidly and randomly

when systems have higher entropy they are

more stable as they’re energy is spread out

when ΔS is postive

there is an increase in entropy

when ΔS is negative

there is a decrease in entropy

how to calculate ΔS

ΔS products - ΔS reactants

what is gibbs free energy equation

ΔG = ΔH - TΔS

for a reaction to become feasible

ΔG is less than or equal to 0

when calculating ΔG

divide ΔS by 1000 to keep units as KJ mol-1