Definitions Flashcards
2nd Ionisation Energy
- Loss of one mole of electrons
- from one mole of singly positively charged ions
- Na^+ (g) -> Na^2+ + e^-
Delta H = Positive
Define the term ‘First Electron Affinity’
- Standard Enthalpy Change
- When 1 mole of gaseous atoms is converted into 1 mole of gaseous ions
- Each with a single negative charge
O(g) + e- => O^- (g)
Delta H = Negative
Second Electron Affinity
- Enthalpy Change
- When 1 mole of electrons is added to 1 mole of gaseous ions
- Each with a single negative charge
- To form ions each with two negative charges
O-(g) + e- => O^2- (g)
Delta H = positive
Lattice Formation Enthalpy
- Standard enthalpy change
- When 1 mole of solid ionic compound is formed from its gaseous ions
E.g. Na+ (g) + Cl- (g) => NaCl (s)
Delta H = Negative
Enthalpy of Lattice Dissociation
-When one mole of ionic compound separates into it’s gaseous ions
Delta H = Positive
Enthalpy of Hydration
- Standard enthalpy change
- When water molecules surround one mole of gaseous ions
Na+ + aq => Na+ (aq)
Delta H = Negative
Cl- + aq => Cl- (aq)
Delta H = negative
Enthalpy of solution
- Standard enthalpy change
- When one mole of solute dissolves completely in sufficient solvent
- to form solution greater than molecules/ions far enough apart not to interact with each other
- NaCl (s) + aq => Na+(aq) + Cl-(aq)
Delta H = Positive
Mean Bond Enthalpy
- Enthalpy Change
- When one mole of gaseous molecules each breaks a covalent bond to form two free radicals
- Averaged over a range of compounds
CH4 (g) => C(g) + 4H (g)
Delta H = Positive
Define the term ‘First Ionisation Energy’
- Standard Enthalpy Change
- when one mole of gaseous atoms is converted into one mole of gaseous ions
- each with a single positive charge.
Na(g) -> Na^+ (g) + e^-
Delta H = Positive
Define: Entropy
- Measure of the amount of disorder in a system
- number of ways that particles can be arranged and the number of ways that energy can be shared out between particles
Ways in which entropy can be increased?
- Changing from liquid to gas
- Changing from solid to liquid
- Solid dissolving in water
- reaction that results in an increased number of particles.
Explain why entropy changes mean that an endothermic reaction can happen spontaneously.
- Enthalpy is not the only factor to affect entropy.
- Changing states and number of molecules affect entropy
- if increase in entropy due to other factors is greater than the decrease in entropy due to the reaction being endothermic
- overall entropy change will be positive
- reaction happen spontaneously
Delta G I always negative since.
- Reaction is exothermic (negative delta H) and has a positive entropy change
- Delta G = Delta H - Temperature*DeltaSystem
Delta G is always positive when
- reaction is endothermic
- negative entropy change
- reactions not feasible at any temperature.
Delta H Is positive and Delta S is positive then reaction won’t be feasible at some temps but will be at higher temps.
