Definitions Flashcards
(40 cards)
Define enthalpy of formation
The energy required to form one mole of product from its constituent atoms in their standard states under standard conditions.
What elements are liquid in standard state?
Mercury and Bromine.
What elements are solid in standard state?
All other elements.
What elements are gases in standard state?
Noble gases. Fluorine, chlorine, hydrogen, oxygen, nitrogen. (exist as diatomic molecules)
Define enthalpy of combustion
The energy released when 1 mole of a substance is completely burnt in oxygen under standard conditions.
Define enthalpy of vaporisation
Energy needed to break through enough of the weakest forces between the particles in one mole of a liquid at its boiling point to form a gas. (always positive)
Define enthalpy of sublimation
Energy needed to break the forces between the particles to convert one mole of solid to a gas. (largest) (always positive)
Define enthalpy of fusion
Energy needed to break enough of the weakest forces between the particles in one mole of a solid at its melting point to form a liquid. (always positive)
What does q represent in q = MCAT
Heat absorbed or given off (J or kJ) BY THE WATER
delta RH represents heat absorbed/given off PER MOLE
(BY THE REACTION)
If temp of water decreases…
q is negative. Reaction is endothermic. Delta R h is positive.
If temp of water increases…
q is positive. Reaction is exothermic. Delta R h is negative.
What is delta r h?
Heat change per mole of reactant. (enthalpy change during a reaction).
what is enthalpy?
Heat transferred during a chemical rxn
What is entropy?
A measure of the extent of disorder of energy or matter.
Define spontaneous. When is a reaction spontaneous
Those that can occur by themselves without any external help e.g: extra input of energy. When exothermic (delta H negative, and entropy increasing +ve).
when delta H - T delta S is negative
Define non-spontaneous. When is a reaction non-spontaneous
Those that cannot occur by themselves. They need external help, an extra input of energy. When endothermic (delta H positive, and entropy decreasing -ve).
when delta H - T delta S is positive
What is an ionic bond? Describe ionic solids.
The strong electrostatic force of attraction between cations and anions.
- giant 3D lattice
- high MP/BP
- conductor when molten
- brittle
- more soluble in polar than non-polar
Describe metallic solids.
3D lattice of metal atoms.
Delocalised valence e- moving between layers. (conductor)
bond = electrostatic attraction between +ve metal ions, and valence e- sea.
intermolecular forces increase w/greater molar mass
malleable, ductile due to delocalised electrons.
Describe temporary dipole attractions
In ALL MOLECULES, electrons are in constant motion.
Therefore at any instant, arrangement of electrons about nucleus is not symmetric. More e- density on one side than other. = creates an instantaneous dipole.
(Atoms with ID attract electrons in neighbouring atoms. This gives them an induced dipole. = attracts them to each other)
Describe permanent dipole attractions
POLAR molecules have polar bonds arranged asymmetrically around central atom.
Charge distributed unevenly, therefore they have permanent dipoles.
(these additional dipole dipole attrc. forces means it takes more energy to break).
Describe hydrogen bonding
Occurs with HF HO HN.
Type of PD-PD bond.
3 most EN elements, small atoms. Therefore VERY concentrated charge.
F/O/N strong polarising effect on hydrogen atom, which is left as an exposed proton. This exerts a strong positive attraction to e- of neighbouring molecules.
Define first ionisation energy
The energy required to remove one mole of the most loosely held electrons from 1 mole of atoms in the gaseous state.
Define electronegativity
The ability of an atom to attract a pair of bonding electrons to itself.
Define atomic radius
Half the distance between the nuclei of two neighbouring atoms.
