5.2 Flashcards
What is the lattice enthalpy, ∆LEH?
The energy change during the formation of 1 mol of ionic lattice from gaseous ions.
When the lattice enthalpy is higher, so is the strength of the ionic bonding in a lattice.
What is the enthalpy change of solution, ∆solH?
The energy change when 1 mol of solute is completely dissolved in water under standard conditions.
What is the enthalpy change of hydration ∆hydH?
The energy change when 1 mol of gaseous ions are dissolved in water
born harbour cycles for the lattice enthalpy change and enthalpy change of solution
What factors affect the lattice enthalpy and enthalpy of hydration?
The smaller the ions the higher the charge density so the stronger the electrostatic attractions between the oppositely charged ions so the more exothermic the lattice enthalpy (or enthalpy of hydration)
The higher the charge on the ions the higher the charge density so the stronger the electrostatic attractions between the oppositely charged ions so the more exothermic the lattice enthalpy (or enthalpy of hydration)
What is entropy?
A measure of the dispersal of energy in a system which is greater, the more disordered a system.
Entropy increases:
solids -> liquids -> gas
a solid dissolves
the number of moles of gas increases in a reaction.
How can entropy be calculated?
ΔS = total entropy of products – total entropy of reactants
How is the feasibility of a reaction calculated and what are the flaws of this method?
A reaction is feasible when ΔG is negative:
ΔG = ΔH -TΔS
where ΔH and ΔS are in kJ
However, even if ΔG is negative a reaction may not take place if the rate of reaction is too slow or the activation energy is too high.
What is the standard electrode potential?
The emf of a half cell compared with a standard hydrogen half cell measured at 298K with solution concentrations of 1 mol/dm3 and a gas pressure of 101kPa
[half cell diagrams for: metal/ions, ions/ions, gas/ions]
What is the salt bridge?
A strip of filter paper soaked in potassium nitrate (which doesn’t react/ form precipitates with any of the half solutions). It completes the circuit, allowing ions to flow, but not electrons.
What is the purpose of the platinum electrode?
The platinum (inert) electrode allows the contact between the gas and the aqueous ions, allowing for the transfer of electrons.
What’s the standard of the electrochemical series?
The redox reactions are always written as reductions (with electrons on the left hand side)
What does a (more) negative electrode potential indicate?
The cell with the more negative electrode potential is the negative terminal. It’s equilibrium will go from right to left and release electrons.
(This is an explanation for solubility (+diagrams))
What is the cell potential?
The difference between the electrode potentials.
