State of phosphorus: solid
state of sulfur:solid
TREND OF MELTING POINT FOR ELEMENTS IN PERIOD 3:
Melting points generally increase going from sodium to silicon, then decrease going to argon.
melting involves breaking up the lattice structure of a solid. hence, the melting point of an element indicates the strength of forces holding the particles together in the crystal lattice.
melting point increases from Na to Al as the strength of the metallic bond increases,
Si has a very high melting point due to its giant covalent structure. A large amount of energy is required to break the strong covalent bonds in Si.
P, S, Cl and Ar have lower melting points since they are simple molecules with weak van der Waals' forces between molecules.
Sunday, August 23, 2009
Sunday, August 9, 2009
Energetics
DEFINITIONS:
Standard enthalpy change of reaction: Enthalpy change when molar quantities of reactants, as stated in the balanced stoichiometric equation, react together.
Standard enthalpy change of neutralisation: Enthalpy change when one mole of water is formed during the neutralisation between an acid and a base under standard conditions of 1atm and 298k.
Standard enthalpy change of formation: Enthalpy change when one mole of a pure compound is formed from its constituent elements in their standard states under standard conditions of 1 atm and 298k.
Standard enthalpy change of combustion: Enthalpy change when one mole of a substance is completely burnt in excess oxygen under standard conditions of 1atm and 298k.
Standard enthalpy change of atomisation: Enthalpy change when one mole of separate gaseous atoms are produced from the element in its standard state under standard conditions of 1 atm and 298k.
Standard enthalpy change of hydration: Enthalpy change when 1 mole of free gaseous ions is surrounded by water molecules and form a solution at infinite dilution, under standard conditions of 1atm and 298k.
Standard enthalpy change of solution: Enthalpy change when 1 mole of solute is completely dissolved in a solvent to form an infinitely dilute solution under standard conditions of 1 atm and 298k.
Bond dissociation energy: Energy required to break one mole of covalent bonds between 2 atoms in the gaseous state.
First ionisation energy: minimum energy required to remove one mole of electrons from one mole of gaseous atoms producing one mole of gaseous singly charged positive ions.
Electron affinity: Enthalpy change when one mole of gaseous atoms or negatively charged ion gain one mole of electrons.
Lattice energy: Enthalpy change when 1 mole of an ionic crystalline solid is formed from its separate gaseous ions under standard conditions of 1atm and 298k.
Standard enthalpy change of reaction: Enthalpy change when molar quantities of reactants, as stated in the balanced stoichiometric equation, react together.
Standard enthalpy change of neutralisation: Enthalpy change when one mole of water is formed during the neutralisation between an acid and a base under standard conditions of 1atm and 298k.
Standard enthalpy change of formation: Enthalpy change when one mole of a pure compound is formed from its constituent elements in their standard states under standard conditions of 1 atm and 298k.
Standard enthalpy change of combustion: Enthalpy change when one mole of a substance is completely burnt in excess oxygen under standard conditions of 1atm and 298k.
Standard enthalpy change of atomisation: Enthalpy change when one mole of separate gaseous atoms are produced from the element in its standard state under standard conditions of 1 atm and 298k.
Standard enthalpy change of hydration: Enthalpy change when 1 mole of free gaseous ions is surrounded by water molecules and form a solution at infinite dilution, under standard conditions of 1atm and 298k.
Standard enthalpy change of solution: Enthalpy change when 1 mole of solute is completely dissolved in a solvent to form an infinitely dilute solution under standard conditions of 1 atm and 298k.
Bond dissociation energy: Energy required to break one mole of covalent bonds between 2 atoms in the gaseous state.
First ionisation energy: minimum energy required to remove one mole of electrons from one mole of gaseous atoms producing one mole of gaseous singly charged positive ions.
Electron affinity: Enthalpy change when one mole of gaseous atoms or negatively charged ion gain one mole of electrons.
Lattice energy: Enthalpy change when 1 mole of an ionic crystalline solid is formed from its separate gaseous ions under standard conditions of 1atm and 298k.
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