Definitions Flashcards
Half-life (t1/2)
The time taken for the concentration of a reactant to half.
Order
A number that relates the rate of a reaction to the concentrations of each reactant.
Overall Order
The sum of the orders with respect to each reactant.
Rate Constant (k)
A constant value that relates the rate of a reaction at a given temperature to the concentrations of the reactants. For a first order reaction, this can be determined using
the relationship k = ln 2/t1/2.
Rate-determining Step
The slowest step of a reaction.
Rate equation
Relates rate to the concentrations of the reactants multiplied by the rate constant. Each concentration is raised to the power of the order with respect to that reactant.
Rate of Reaction
A measure of how quickly a reactant is used up / a product is formed.
Reaction Mechanism
A step-by-step sequence of the individual reactions that make up the overall reaction.
Equilibrium Constant (K)
A value that relates the amount of products and reactants at equilibrium in a reversible reaction at a specific temperature. K is unaffected by pressure and presence of a catalyst but is affected by temperature.
Buffer Solution
A system that minimises pH change on addition of small amounts of an acid or base. A buffer solution can be formed from a weak acid and a salt of the weak acid or from excess weak acid and a strong alkali.
Carbonic Acid-Hydrogencarbonate Buffer
The buffer system present in blood plasma,
used to maintain blood pH between 7.35 and 7.45.
Conjugate Acid-Base Pair
A pair of compounds that transform into each other by the transfer of a proton. Conjugate acid-base pairs are important in the formation of buffers to control pH.
End Point
The point during a titration when the indicator changes colour. A suitable indicator should change colour near the equivalence point (it should have a pH range within the vertical section of the titration curve).
Equivalence Point
The point during a titration when the amount of acid is exactly equal to the amount of base (full neutralisation occurs). When titrating an acid with a base, [H+ ] is equal to [OH− ] at this point.
Indicator
A weak acid that changes colour with changing pH due to an equilibrium shift between HA and A-. For an indicator to be suitable, its pH range must be within the vertical section of the titration curve (there is no suitable indicator for weak acid-weak base titration as the titration curve does not have a vertical section)
Born-Haber Cycle
A cycle which can be used to calculate the lattice enthalpy of an ionic compound using other enthalpy changes.
Enthalpy (H)
A value that represents the heat content of a system.
Enthalpy Change (ΔH)
The change in the heat content of a system during a reaction.
Enthalpy Change of Atomisation (ΔH)
The enthalpy change that takes place when one mole of gaseous atoms is formed from an element in its standard state.
Enthalpy Change of Formation (ΔfH)
The enthalpy change that takes place when one mole of a compound is formed from its elements.
Enthalpy Change of Hydration (hydH)
The enthalpy change that takes place when one mole of gaseous ions are dissolved in water (exothermic). Increasing ionic charges and decreasing ionic radii make this value more negative as there would be greater attraction between the water molecules and the ions.
Enthalpy Change of Solution (solH)
The enthalpy change that takes place when one mole of solute is dissolved.
First Electron Affinity
The amount of energy released when one mole of electrons is added to one mole of gaseous atoms, forming one mole of 1- ions.
First Ionisation Energy
The removal of one mole of electrons from one mole of gaseous atoms to form one mole of 1+ ions.
Ionic Bond
Electrostatic attraction between positive and negative ions.
Giant Ionic Lattice
A regular repeating structure made up of oppositely charged ions.
Lattice Enthalpy (ΔLEH)
The formation of one mole of an ionic lattice from gaseous ions. Lattice enthalpy is used as a measure of the strength of ionic bonds in a giant lattice, with a more negative value meaning stronger bonds. Increasing ionic changes and decreasing ionic radii make this value more negative as there would be greater attraction between the ions.
