definitions Flashcards
Rate of reaction
Change in concentration of a reactant or product over time
Order
Power a concentration of a reactant is raised to in a rate equation, matching its stoichiometry in the RDS
Overall order
The sum of all orders in the rate equation
Rate constant
k in Rate = k[A]m[B]n…
Half-life
Time taken for the concentration of a reactant to reduce by half
Rate determining step
The slowest step in a reaction mechanism
Mole fraction
Moles of gas divided by the total moles of all gases
Partial pressure
Pressure from gas divided by the total pressure from all gasses
Brønsted-Lowry acid
donates a proton
Brønsted-Lowry base
accepts a proton
Monobasic acid
one mole of acid dissociates to form one mole of H+ ions
Dibasic acid
one mole of acid dissociates to form two moles of H+ ions
Tribasic acid
one mole of acid dissociates to form 3 moles of H+ ions
Buffer solution
A system that minimises pH changes on addition of small amounts of an acid or base
Oxidising agent
Oxidises another element, it is itself reduced
Reducing agent
Reduces another element, it is itself oxidised
Standard electrode (redox) potential, Eθ
The EMF of a half-cell compared to a standard hydrogen electrode under standard conditions, 298 K, 100 kPa and 1 mol dm-3
Transition elements
d-block elements that have a stable ion with an incomplete d-sub-shell
Ligand
A molecule or ion that can donate a lone pair to form a coordinate (dative covalent) bond to a metal ion or metal
Bidentate ligand
A molecule or ion that can donate two lone pairs to form two coordinate (dative covalent) bond to a metal ion or metal
Complex ion
Metal cation surrounded by coordinately bonded ligands
Coordination number
Total number of coordinate bonds formed with the central metal ion
Entropy
A measure of the dispersal of energy in a system which is greater the more disordered a system
which enthalpy term can be either endo or exothermic
enthalpy of formation and solution
which enthalpy terms are always exothermic
- first electron affinity
- lattice enthalpy
- enthalpy change of hydration
Enthalpy change of hydration
- Dissolving of 1 mol of gaseous ions in water, ∆hydH
- K+ (g) —-> K+ (aq)
- exothermic as water molecules surround ions to form new forces of attraction. Energy is released.
Enthalpy change of solution
KCl
- Dissolving of 1 mol of solute in water, ∆solH
- KCl (s) —> K+ (aq) + Cl- (aq)
- endo/exothermic as ‘amount of heat’ released or absorbed in the dissolving process depends on whether the lattice enthalpy or hydration enthalpy is greater.
enthalpy of atomisation, ΔatH
F
- ΔH when 1 mol of gaseous atoms is formed from its element
- 1/2 F2 (g) —-> F (g)
- endothermic only as energy required to break bonds between the atoms of an element.
bond enthalpy
CF4
- enthalpy required to break 1 mol of a specific gaseous covalent bond
- 1/4 CF4 (g) —> 1/4 C (g) + F (g)
- endothermic only as energy required to break bonds between the atoms.
first electron affinity ΔEA1H
Cl
- enthalpy released when 1 mol of gaseous atoms gains 1 mol of e- to form one mole of gaseous 1- ions
- Cl (g) + e- —> Cl- (g)
- mostly exothermic because electrostatic attraction between +ve nuclei and -ve e- formed. Can be +ve if it doesn’t form a stable ion
second electron affinity ΔEA2H
S
- enthalpy released when 1 mol of 1- gaseous ions gains 1 mol of e- to form one mole of gaseous 2- ions
- S- (g) + e- —> S^2- (g)
- always endothermic as repulsion is being forced between to -ve charges
- Increased electron-electron repulsions in a dianion > the attraction of electrons to the nucleus. Electrostatic repulsion from negative ion and the electron being gained.
lattice enthalpy, ΔLEH
NaCl
- ΔH when 1 mol of an ionic compound is formed from its gaseous ions
- Na+ (g) + Cl- (g) —> NaCl (s)
- always exothermic because bonds formed by ions combining, large release of energy. Ionic compound more stable than its gaseous ions.
- Strong electrostatic forces of attraction between oppositely charged ions
Enthalpy of formation, ΔfH
- one mole of a compound from its constituent elements
- Na (s) + ½ Cl2 (g) —> NaCl (s) ΔHfꝋ
- endo/exothermic because:
Bonds broken – bonds formed = overall enthalpy change
