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1.2.3 standard enthalpy changes of combustion and formation (HL)

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chem whatdriveschemicalreactions

Reactivity 1.2.3 - standard enthalpy changes of combustion , and formation, , data are used in thermodynamic calculations
standard enthalpy change of combustion:
  • the enthalpy change that occurs when one mole of the substance burns under standard conditions
standard enthalpy change of formation:

  • the enthalpy change that occurs when one mole of the substances is formed from its elements in their standard states

  • the standard state of an element is its most stable form under standard conditions

  • the standard enthalpy change of formation of a substance is zero when it is an element in its standard state. (Si)

challenge questions
  1. suggest, based on the discussion of bonding and structure in structure 2.2, why graphite is more stable than diamond

graphite is more stable than diamond as the bond order is 1.5, coordination number is 3, weak intermolecular forces between layers. in diamond, each carbon is bonded to four other atoms by single covalent bonds, the total bonding is slightly stronger in graphite