Chem Energetics

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Standard enthalpy change of reaction (∆Hr)

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Enthalpy change of reaction is the energy change in any specific chemical reaction as defined by the stoichiometric thermochemical equation and the value of energy change refers to the amounts (moles) if the substance and their states in that specific equation.

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Standard enthalpy change of formation (∆Hf∅)

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Standard enthalpy change of formation is the energy change when one mole of substance is formed from its constituent elements in their standard states at 298K and 1 bar

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Standard enthalpy change of combustion (∆Hc∅)

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Standard enthalpy change of combustion is the energy evolved when one mole of substance is burnt completely in excess oxygen at 298K and 1 bar

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Standard enthalpy change of neutralisation (∆Hneu∅)

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Standard enthalpy change of neutralisation is the energy evolved when one mole of water is formed in the reaction between an acid and a base at 298K and 1 bar.

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Standard enthalpy change of atomisation of an element(∆Hatom∅)

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Standard enthalpy change of atomisation of an element is the energy absorbed when one mole of gaseous atoms is formed from the elements at 298K and 1 bar.

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Standard enthalpy change of atomisation of a compound (∆Hatom∅)

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Standard enthalpy change of atomisation of a compound is the energy absorbed when gaseous atoms are formed from one mole of the compound at 298K and 1 bar

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Bond energy (BE)

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Bond energy is the energy absorbed when one mole of a given covalent bond in a gaseous compound is broken into gaseous atoms or molecules

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Lattice energy (LE)

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Lattice energy is the energy evolved when one mole of ionic solid is formed from its constituent gaseous ions (at infinite distance apart)

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Enthalpy change of hydration/ hydration energy (∆Hhyd)

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Enthalpy change of hydration is the energy evolved when one mole of gaseous ions is converted to one mole of aqueous ions at infinite dilution.

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Enthalpy change of solution (∆Hsol)

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Enthalpy change of solution is the energy change when one mole of substance (in its standard state) is completely dissolved in infinite dilution in an aqueous solution

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Ionisation energy (IE)

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First ionisation energy is the energy absorbed to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of singly charged positive gaseous ions

Second ionisation energy is the energy absorbed to remove one mole of electrons from one mole of singly charged positive gaseous ions of an element to form one mole of doubly charged positive gaseous ions

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Electron affinity (EA)

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First electron affinity is the heat change when one mole of gaseous atoms of an element gain one mole of electrons to form one mole of singly charged negative gaseous ions

Second electron affinity is the heat change when one mole of singly charged negative gaseous ions of an element gain one mole of electrons to form one mole of doubly charged gaseous ions