F325 Module 2: Energy

Definitions of key terms :)

Standard conditions are assumed to be 298K, 101kPa, 1 moldm-³

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  • Created by: Anabuddy
  • Created on: 12-09-12 19:55

Standard Entropy of Reaction, ΔSº

The entropy change that accompanies a reaction in the molar quantities expressed by the reaction, under standard conditions and reactants and products all in their standard states. Measured in Jmol-¹K-¹

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Free Energy Change, ΔG

The balance between enthalpy, entropy, and temperature for a process:

  • ΔG= ΔH-TΔS

A process can take place spontaneously when ΔG < 0

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Lattice Enthalpy, ΔHº (LE)

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions, under standard conditions. Measured in kJmol

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Standard Enthalpy change of Formation, ΔHº(f)

The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states, under standard conditions. Measured in kJmol-¹

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Standard Enthalpy Change of Atomisation, ΔHº(at)

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state. This is an endothermic reaction. Measured in kJmol-¹

  • Li(s) Li(g) ΔH= +161 kJmol-¹
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First Ionisation Energy, ΔHº(i₁)

The energy required to remove one electron from each atom in one mole of gaseous atoms, under standard conditions. Measured in kJmol-¹

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Standard Electron Affinity, ΔHº(ea₁)

The enthalpy change when each atom in a mole of atoms gains one electron to form one mole of gaseous -1 ions, under standard conditions. (N.B. Second electron affinity can often be endothermic, because of the repulsion of the 1- ion, so more energy needs to be put in to overcome the repulsion). Measured in kJmol-¹

  • F(g) + e- → F-(g)
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Standard Enthalpy Change of Solution, ΔHº(sol)

The enthalpy change when one mole of a compound is dissolved in water, under standard conditions. Usually small, and can be endothermic or exothermic, depending on the strength of the solid structure. Measured in kJmol-¹

  • NaCl (s) + (aq) → Na+ (aq) + Cl- (aq)
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Standard Enthalpy Change of Hydration, ΔHº(hyd)

The enthalpy change when one mole of aqueous ions are formed from one mole of gaseous ions, under standard conditions. Measured in kJmol-¹

  • Na+ (g) → Na+ (aq)

The value of the ΔHº(hyd) gives an idea of the strength of the attraction between the ion and the water molecule. 

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