A2: Thermodynamics Flashcards
Why does Silver Fluoride have a LARGER Enthalpy of Dissociation than Silver Chloride?
F ION smaller than Cl ION
F ION has a HIGHER CHARGE DENSITY
Attraction between Ag+ and F- STRONGER
Why is the THEORETICAL value different to the EXPERIMENTAL value?
~ EXPERIMENTAL VALUE allows for NON-SPHERICAL ions
~ THEORETICAL value assumes PERFECT SPHERES ions
Define: Enthalpy of Hydration
ENTHALPY CHANGE
when 1 mol of gaseous IONS
forms aqueous IONS
Why is hydration an EXOthermic process?
water is POLAR
Cl ION attracts the H in water molecules
Why is the ELECTRON AFFINITY of fluorine a NEGATIVE value?
~ There is an attraction between the nucleus / protons and the added electron(s)
~ Energy is released when electron is GAINED
Define “bond dissociation enthalpy”
ENTHALPY CHANGE to break the bond in 1 mol of a covalent bond to FORM 2 moles of GASEOUS atoms
Define “Lattice Enthalpy of Dissociation”
enthalpy change to separate 1 mole of an ionic lattice into its ions, in the gaseous phase
Define “Perfect Ionic Model”
- ions are perfect spheres
- ions are pin point charges
- NO covalent character
- only electrostatic attraction
Properties that influence the value of a lattice enthalpy calculate using the Perfect Ionic Model:
- distance between ions
* ionic charge
Why is the entropy zero when the temperature is zero?
- at 0 temperature, particles are STATIONARY 🚉
* no disorder
Why is the entropy of water zero at 0 K?
no disorder
Write an expression between free-energy change, enthalpy change and entropy change
G = H – TS
CH4(g) + 2H2O(g) –> CO2(g) + 4H2(g)
Why does entropy increase in this reaction?
- The number of MOLES of gas increases from 3 to 5
- More moles of GAS gives more DISORDER
Define “Feasible reaction”
One for which G O
Define “enthalpy change”
- Heat energy TRANSFERRED in a reaction at CONSTANT PRESSURE
