Chemistry unit 4 definitions

Frage	Antworten
Rate of reaction	The change in concentration of product/ reactant per unit of time
Initial rate of reaction	The change in concentration of a reactant, or product per unit of time at the start of the reaction when time = 0
Rate equation	A reaction (2A + B -> C) becomes rate=k[A]^2[B]
Order of a reaction	A reactant to the power of the concentration of the reactant is raised to in the rate equation
Overall order	Sum of all the orders
Rate constant k	Constant that links the rate of reaction to the concentration of the reactants raised to the powers of their orders in the rate equation
Half-life	The time taken for the concentration of the reactant to reduce by a half
Reaction mechanism	The series of steps that together make up the overall reaction
Rate-determining step	The slowest step in the reaction mechanism of a multi step reaction
Intermediate species	A species formed in one step of a multi-step reaction that is used in the next step, it is not seen as either a reactant or product of the overall reaction
Equilibrium law	aA +bB -> cC + dD Kc = [C]^c[D]^d ---------------- [A]^a[B]^b
Dynamic equilibrium	Equilibrium that exists in a closed system where the rate of the forward reaction is equal to the rate of the backwards reaction
Homogenous equilibrium	Equilibrium in which all the reactant and products are in the same physical state
Heterogeneous equilibrium	Equilibrium in which the reactant and products are in different physical state
le Chatelier's principle	When a system is in dynamic equilibrium and the conditions are changes, the position of equilibrium will shift to minimise the change
Bronsted - Lowry acid	A proton donor
Bronsted - Lowry base	Proton acceptor
Alkali	A base that dissolves in water forming OH-(aq) ions
Neutralisation	A chemical reaction in which an acid and base react together to produce a salt and water
Acid - base pair	A pair of two species that transform into each other by gain or loss of a proton
pH	-log[H+(aq)] where [H+(aq)] = 10^-pH
Strong acid	An acid that completely dissociates in solution
Weak acid	An acid that partially dissociates in solution
Acid dissociation constant, Ka	Ka = [H+(aq)][A-(aq)] ---------------------- [HA(aq)]
pKa	pKa = -log10 Ka Where Ka = 10^-pKa
Ionic product of water, Kw	Kw = [H+(aq)][OH-(aq)] at 25'C, Kw = 1.00 x 10^-14 mol^2dm^-6
Buffer solution	Mixture that minimises pH changes on addition of small amounts of acid or base
Equivalence point	The point in a titration where the volume of one solution has reacted exactly with the volume of the second solution This matches the stoichiometry of the reaction taking place
End point	The point in a titration where there are equal concentrations of the weak acid and conjugate base forms of the indicator The colour at the end point is midway between the colours of the acid and conjugate base forms
Standard enthalpy change of neutralisation	The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H2O under standard conditions
Lattice enthalpy	The enthalpy change that accompanies the formation of one mole of an ionic compound that its gaseous ions under standard conditions
Hess' law	If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
Standard enthalpy change of formation	The enthalpy change that takes place when forming one mole of a compound from its constituent in their standard state in standard conditions
Enthalpy change of atomisation	The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state
First ionisation energy	The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
First electron affinity	The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
The standard enthalpy change of a solution	The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
The standard enthalpy change of hydration	The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
Entropy, S	The quantitative measure of the degree of disorder in a system
Standard entropy change of a reaction	The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states
Free energy change	The balance between enthalpy, entropy and temperature for a process ∆G=∆H - T∆S A process that can take place spontaneously when ∆G<0
Oxidation	Loss of electrons or an increase in oxidation number
Reduction	Gain of electrons or decrease in oxidation number
Standard electrode potential	The E.M.F of a half cell compared with the standard hydrogen half cell measured at 298K with solution concentration of 1 mol dm^-3 and a gas preasure 100kPa(1 atmosphere)
Transition element	d-block element that forms an ion with an incomplete d sub-shell
Complex ion	Transition metal ion bonded to one or more ligands by coordinate bonds
Ligand	Molecule or ion that donates a lone pair of electrons to the transition metal ion to form a coordinate bond
Coordination number	The total number of coordinate bonds formed between a central metal ion and its ligands
Stereoisomers	Species with the same structural formula but with a different arrangement of the atoms in space
Ligand substitution	A rection in which one ligand in a complex ion is replaced by another ligand
Stability constant, Kstab	Equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution

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