Enthalpy definitions Flashcards
What is the enthalpy change of formation?
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
Example: 2C(s) + 3H2(g) + ½ O2(g) 🡪 C2H5OH(l)
What does Δ Hf represent?
Enthalpy change of formation.
What is the enthalpy change of atomisation?
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.
Example: ½ Cl2(g) 🡪 Cl(g)
What does Δ Hat stand for?
Enthalpy change of atomisation.
What is the first ionisation enthalpy?
The enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms.
Example: Mg(g) 🡪 Mg+(g) + e-
What does Δ Hie1 denote?
First ionisation enthalpy.
What is the second ionisation enthalpy?
The enthalpy change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.
Example: Mg+(g) 🡪 Mg2+(g) + e-
What does Δ Hie2 represent?
Second ionisation enthalpy.
What is the first electron affinity?
The enthalpy change when 1 mole of gaseous 1- ions is made from 1 mole of gaseous atoms.
Example: O(g) + e- 🡪 O-(g)
What does Δ Hea1 stand for?
First electron affinity.
What is the second electron affinity?
The enthalpy change when 1 mole of gaseous 2- ions is made from 1 mole of gaseous 1- ions.
Example: O-(g) + e- 🡪 O2-(g)
What does Δ Hea2 denote?
Second electron affinity.
What is the enthalpy change of hydration?
The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions.
Example: Na+(g) 🡪 Na+(aq)
What does Δ Hhyd represent?
Enthalpy change of hydration.
What is the enthalpy change of solution?
The enthalpy change when 1 mole of solute is dissolved in sufficient solvent that no further enthalpy change occurs on further dilution.
Example: NaCl(s) 🡪 NaCl(aq)
What does Δ Hsol stand for?
Enthalpy change of solution.
What is the enthalpy of combustion?
Energy change when 1 mole of a substance is completely burnt in oxygen under standard conditions.
Example: CH4(g) + 2 O2(g) 🡪 CO2(g) + 2H2O(l)
What does Δ Hc denote?
Enthalpy of combustion.
What is the enthalpy of dissociation?
Standard molar enthalpy when a covalent bond is broken in a gaseous molecule to form 2 gaseous free radicals.
Example: CH4(g) 🡪 CH3(g) + H(g)
What does Δ Hdiss represent?
Enthalpy of dissociation.
What is mean bond enthalpy?
The average amount of energy needed to break a specific type of bond measured over a variety of different molecules.
Example: C-H in CH4, C2H6 and C3H8
What is the latent enthalpy of fusion?
The change in enthalpy resulting from heating a given quantity of a substance to change its state from a solid to a liquid. The temperature at which this occurs is the melting point.
What does Δ Hfus denote?
Latent enthalpy of fusion.
What is the enthalpy of sublimation?
Enthalpy change when 1 mole of gaseous atoms is formed from a solid element.
Example: Na(s) 🡪 Na(g)
What does Δ Hsub stand for?
Enthalpy of sublimation.
What is the enthalpy of lattice dissociation?
The standard enthalpy change that accompanies the separation of 1 mole of a solid ionic lattice into its gaseous ions.
Example: NaCl(s) 🡪 Na+(g) + Cl-(g)
What does Δ HL represent?
Enthalpy of lattice dissociation (always +).
What is the enthalpy of lattice formation?
The standard enthalpy change that accompanies the formation of a solid ionic lattice from its gaseous ions.
Example: Na+(g) + Cl-(g) 🡪 NaCl(s)
What does Δ HL represent in this context?
Enthalpy of lattice formation (always -).
