Chem Energetics definitions

Standard enthalpy change of combustion is defined as the enthalpy change when

• 1 mole of compound is burnt in oxygen.

• 1 mole of compound is completely burnt in oxygen under standard conditions of 298K and 1 bar.

• 1 mole of compound is burnt under oxygen at 293K and 1 bar.

• 1 mole of oxygen is used to burn a compound under standard conditions of 298K and 1 bar.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

Standard enthalpy change of neutralisation is defined as the enthalpy change when

• 1 mole of acid reacts with 1 mole of alkali to form 1 mole of water, under standard conditions of 298K and 1 bar.

• 1 mole of water is formed in the neutralisation between an acid and an alkali, under standard conditions of 298K and 1 bar.

• 1 mole of water is formed in the neutralisation between an acid and an alkali, the reaction being carried out in aqueous solution under standard conditions of 298K and 1 bar.

• 1 mole of acid is neutralised by an alkali to form a salt and water, under standard conditions of 298K and 1 bar.

Bond energy (of dissociation) (BE) is defined as 

• the enthalpy change when 1 mole of covalent bonds is broken.

• the energy required to break 1 mole of a covalent bond between two atoms in the gaseous state.

• the energy required to break covalent bonds between atoms in the gaseous state to form 1 mole of gaseous atoms.

• the energy released when 1 mole of covalent bond between two atoms in the gaseous state is formed.

Bond energy (of dissociation) (BE) is

• always positive (endothermic)

• always negative (exothermic)

• sometimes positive and sometimes negative

• double the value of  $\Delta H\ atomisation$  for gaseous diatomic molecules

• equal to the value of  $\Delta H\ atomisation$  for gaseous diatomic molecules

Standard enthalpy change of formation of a substance is defined as

• the enthalpy change when 1 mole of the substance is formed from its elements under standard conditions of 298K and 1 bar.

• the energy released when 1 mole of the substance is formed from its elements under standard conditions of 298K and 1 bar.

• the enthalpy change when 1 mole of elements is used to form a substance under standard conditions of 298K and 1 bar.

• the energy released when 1 mole of elements is used to form a substance under standard conditions of 298K and 1 bar.

Standard enthalpy change of hydration

• of a substance is defined as the enthalpy change when 1 mole of the substance is dissolved in a large amount of water under standard conditions of 298 K and 1 bar.

• of a substance is defined as the enthalpy change when 1 mole of the substance is fully dissolved in water under standard conditions of 298 K and 1 bar.

• of an ion is defined as the enthalpy change when 1 mole of ions is dissolved in a large amount of water such that addition of more water produces no further heat change under standard conditions of 298 K and 1 bar.

• of an ion is defined as the enthalpy change when 1 mole of gaseous ions is dissolved in a large amount of water such that addition of more water produces no further heat change under standard conditions of 298 K and 1 bar.

Standard enthalpy change of solution is defined as

• the enthalpy change when 1 mole of a substance is dissolved in a large amount of solvent under standard conditions of 298 K and 1 bar.

• the enthalpy change when 1 mole of an ionic compound is fully dissolved in solvent under standard conditions of 298 K and 1 bar.

• the enthalpy change when 1 mole of substance is dissolved in a large amount of solvent such that addition of more solvent produces no further heat change under standard conditions of 298 K and 1 bar. (ie. further dilution has no effect)

• the enthalpy change when 1 mole of aqueous ions is formed from the dissolution in a large amount of water such that addition of more water produces no further heat change under standard conditions of 298 K and 1 bar.

Lattice energy of an ionic solid is defined as

• the energy change when 1 mole of the ionic solid is formed from its separate ions.

• the heat energy evolved when 1 mole of the ionic solid is formed from its separate gaseous ions.

• the energy required to break 1 mole of ionic bonds to form separate ions.

• the heat energy required to break 1 mole of ionic bonds to form separate gaseous ions.

Standard enthalpy of atomisation is defined as the enthalpy change when

• 1 mole of atoms is formed in a reaction under standard conditions of 298 K and 1 bar.

• 1 mole of separate gaseous atoms of the element is formed from the element under standard conditions of 298 K and 1 bar.

• 1 mole of an element is atomised to form separate gaseous atoms under standard conditions of 298 K and 1 bar.

• 1 mole of a compound is broken down into its individual atoms under standard conditions of 298 K and 1 bar.

First ionisation energy (IE) is defined as 

• the energy change when 1 mole of electrons is removed from 1 mole of atoms to form 1 mole of gaseous cations.

• the energy required to remove 1 mole of electrons from 1 mole of atoms to form 1 mole of gaseous cations.

• the energy required to remove 1 mole of electrons from 1 mole of separate gaseous atoms to form 1 mole of gaseous cations.

• the energy released when 1 mole of electrons is removed from 1 mole of separate gaseous atoms to form 1 mole of gaseous cations.