thermodynamics Flashcards
What happens to electrons during ionic bonding?
Electrons are transferred from metal atoms to non-metal atoms.
What types of ions are formed in ionic bonding?
Positively charged metal ions and negatively charged non-metal ions.
What structure do ions form in ionic compounds?
Ions arrange themselves into a lattice.
What is the main reason the formation of an ionic compound is an exothermic process?
The large amount of energy given out when the lattice forms.
What does the magnitude of the lattice enthalpy indicate?
The overall strength of the ionic bonding.
Why are Born-Haber cycles used?
To calculate lattice enthalpies indirectly.
What is a Born-Haber cycle?
A thermochemical cycle that includes all enthalpy changes involved in the formation of an ionic compound.
What is the enthalpy of formation of elements in their standard states?
Zero enthalpy by definition.
What is the first step in a Born-Haber cycle?
Start with elements in their standard states.
What is the enthalpy of formation of a solid ionic compound?
Negative, so it is downhill in the Born-Haber cycle.
What must be done for a group 2 element in a Born-Haber cycle?
Include first and second ionisation energies.
How do you calculate the enthalpy of formation?
Σ all other enthalpy values (atomisations + ionisations + electron affinities + lattice enthalpy).
What does a greater lattice enthalpy indicate?
Stronger ionic bonding.
What factors do lattice enthalpies depend on?
- Size of ions
- Charge of ions
What types of solvents can ionic solids dissolve well in?
Polar solvents.
What is required to dissolve an ionic compound?
Breaking up the lattice, which requires energy.
What is enthalpy of hydration?
The enthalpy change when ions are solvated by solvent molecules.
What is the formula for calculating solution enthalpies?
ΔsolutionH° = Δlattice enthalpy dissociation H° + ΣΔhydration H°.
What does a negative ΔsolutionH° indicate?
Exothermic, heats up solution.
What is the difference between experimental and theoretical lattice enthalpy?
Experimental values are found through measurements, theoretical values are calculated.
What assumption is made in theoretical lattice enthalpy calculations?
All ions are spherical and have evenly distributed charges.
What does a large difference between experimental and theoretical values indicate?
Greater covalent character of an ionic compound.
What is entropy (S)?
The measurement of disorder/randomness of a system.
What does the 2nd law of thermodynamics state?
Entropy will naturally increase over time.
How do you calculate the change in entropy (∆S)?
∆S = ΣS products - ΣS reactants.
What is the 3rd law of thermodynamics?
The entropy of a substance is zero at absolute zero.
How does entropy vary with temperature?
Entropy increases with temperature.
What is the Gibbs free energy change (∆G) formula?
∆G = ∆H - (T x ∆S/1000).
What does a negative ∆G indicate?
The reaction is feasible.
How does Gibbs free energy change with temperature?
Some reactions may be feasible at one temperature and not at another.
What is the significance of activation energy?
It is the energy required to break bonds, making a reaction endothermic.
What is a thermodynamically unstable substance?
A substance that does not react under standard temperature.
What happens to entropy during state changes?
There are big increases in entropy during melting and boiling.
