Thermodynamics Flashcards
What is Hess’ law?
energy change is the same irrespective of the route taken
What is standard enthalpy of formation?
enthalpy of concentration when one mole of a substance is formed from its elements at 100kPa and all substances are in their standard states
Why does ionic bonding get weaker?
as ionic radius increases
Why does Ca2+ have stronger ionic bonding than Na+?
greater charge and smaller radius, attracts Cl- more strongly
What is standard enthalpy of atomisation?
enthalpy change when one mole of gaseous atoms is formed from their elements at 100kPa in their standard states
What is enthalpy of sublimination?
enthalpy change when one mole of solid is converted into one mole of gas
For metals ONLY, what is the relationship between atomisation and sublimination?
enthalpy of atomisation = enthalpy of sublimination
What is bond dissociation enthalpy?
when one mole of bonds are broken homolytically with all species in the gaseous state
For gaseous diatomic elements like Cl2/F2, what is the relationship between bond dissociation and atomisation, and the exception?
enthalpy of bond dissociation = 1/2 enthalpy of atomisation
NOT TRUE FOR Br2 and I2 as they are NOT gaseous at room temp
What is electron affinity?
enthalpy change when one mole of electrons is added to one mole of gaseous atoms
The first electron affinity is always…
NEGATIVE, EXOTHERMIC due to the attraction of the positive nucleus to the electron being gained
The second electron affinity is always…
POSITIVE, ENDOTHERMIC due to the repulsion between the negative ion and the electron being gained
What is the enthalpy of vaporisation?
enthalpy change when one mole of a liquid is converted into a gas
Give an example of enthalpy of vaporisation?
Br2(l) –> Br2(g)
What is the enthalpy of lattice formation?
enthalpy change when one mole of an ionic lattice is formed from gaseous ions
What is the lattice dissociation enthalpy?
enthalpy change when one mole of ionic lattice is converted into its gaseous ions
The more positive the lattice dissociation enthalpy, the….
stronger the ionic bonds
The more negative the lattice formation enthalpy….
stronger the ionic bonds
What is a Born-Haber cycle?
a closed loop of enthalpy changes, that include lattice enthalpy
When trying to figure out x in a Born-Haber cycle, which direction do you go?
tip —>
Why are lattice enthalpies of dissociation always endothermic?
strong electrostatic bonds between opppositely charged ions are being broken
What is the perfect ionic model?
-ions are perfectly spherical
-only ionic bonding is present
What are two properties of ions that influence the value of a lattice enthalpy using a perfect ionic model?
charge and size of ion
What is the enthalpy of solution?
enthalpy change when one mole of a solid dissolves completely in excess water to form an aqueous solution
What is the enthalpy of hydration?
enthalpy change when one mole of gaseous ions is converted into aqeuous ions
Why are enthalpies of hydration very negative and large?
making strong bonds/making strong ion-dipole interactions between ion and polar water molecules
How do you calculate the enthalpy of solution?
ΔHsol = ΔHlattice dissociation + ΣΔH hydration
Why is the theoretical ΔH L.E less than ΔH L.E experimental?
-due to _____ having ionic bonding with covalent character
Why do silver halides/Ag+/Al3+ have covalent character?
the ions are not spherical, there is a higher charge on positive ion and a smaller radius, which polarises/distorts the negative ions more greatly
Why is the theoretical ΔH L.E around the same as ΔH L.E experimental for group 1 halides?
group 1 halides have ionic bonding only and all ions are spherical
