energetics Flashcards
what is the standard enthalpy change of formation (ΔHf)?
A + B -> 1C
enthalpy change when 1 mole of compound is formed from its constituent elements in their standard states at standard conditions of 298K and 1 bar
*ΔHf of elements are always 0
what is the standard enthalpy change of combustion?
1A + O2 –> CO2 + H2O
the enthalpy change when 1 mole of compound is completely burned in excess oxygen at standard conditions of 298K and 1 bar
what is bond energy?
A-A (g) -> 2A (g)
the enthalpy change to break 1 mole of covalent bonds between 2 atoms in the gaseous state
What is the standard enthalpy change of atomisation?
1/2 A2 -> A (g)
the enthalpy change to form one mole of gaseous atom from the element in its standard state at standard conditions of 298K and 1 bar
What are the 3 formulas to calculate ΔHr?
BE:
ΔHr = BE (rxt) - BE (pdt)
ΔHc:
ΔHr = ΔHc (rxt) - ΔHc (pdt)
ΔHf:
ΔHr = ΔHf (pdt) - ΔHf (rxt)
What is the enthalpy change of neutralisation?
the enthalpy change when an acid reacts with a base to form 1 mole of water in dilute aqueous solution at standard conditions of 298K and 1 bar
How to calculate ΔHr using experimental results?
q (in J) = mcΔT
ΔHr = ± q/n
+ for endo, - for exo
for ΔH neut: n = moles of water formed
for ΔHc: n= moles of species combusted
What is LE?
A+ (g) + B- (g) -> C (s)
enthalpy change when 1 mole of solid ionic compound is formed from its constituent gaseous ions
What is EA?
A (g) + e- -> A-(g)
enthalpy change when 1 mole of gaseous atom gains 1 mole of electrons to form1 mole of gaseous singly charged anion
What is IE?
A (g) -> A+ (g) + e-
the enthalpy change when one mole of gaseous atom loses 1 mole of electrons to form 1 mole of gaseous singly charged cation
What is the standard enthalpy change of hydration?
A+ (g) + aq -> A+ (aq)
enthalpy change when 1 mole of gaseous ions is dissolved in a large amount of water to form 1 mole of aqueous ions at standard conditions of 298K and 1 bar
What is the standard enthalpy change of solution?
A -> B+ (aq) + C- (aq)
enthalpy change when 1 mole of substance is completely disolved in a large excess of solvent to form an infinitely dilute solution at standard conditions of 298K and 1 bar
What is entropy?
it measures the degree of disorder in a system
ΔS = entropy of final state - entropy of initial state
when ΔS > 0, final state is more _____ than initial state
more disordered/less disordered
more disordered
what are the factors affecting entropy?
1) change in temp
- higher temp, more kinetic energy, more ways of distributing energy)
2) change in phase
- gas > liquid > solid
3) change in no. of particles (esp for gases)
- when no. of particles increase, more particles moving randomly, more disorderly
4) mixing of particles
- mixing of gases: more ways for particles to arrange themselves
- dissolving ionic compound in water: entropy of ions increase (breaking ionic lattice), entropy of water decreases (ion-dipole interactions)
