Definitions in AS chemistry


Definitions for AQA AS Chemistry, mostly taken directly from mark schemes.
Stephen Cole
Flashcards by Stephen Cole, updated more than 1 year ago
Stephen Cole
Created by Stephen Cole about 10 years ago

Resource summary

Question Answer
Catalyst Substance which speeds up a chemical reaction but is chemically unchanged at the end
Hess's Law The enthalpy change of a reaction is independent of the route taken
Le Chatelier's Principle If a factor affecting the equilibrium of a reversible reaction is changed, the position of equilibrium will shift in the direction which opposes that change.
Electronegativity The power of an atom to withdraw electron density from a covalent bond
Enthalpy change Change in heat content at constant pressure
Enthalpy A measure of the heat content of a substance
Mean bond enthalpy The enthalpy required to break a covalent bond, averaged over a wide range of compounds
Standard enthalpy of combustion Enthalpy change when 1 mole of a substance is completely burned in oxygen with all reactants and products in standard states under standard conditions
Standard enthalpy of formation Enthalpy change when 1 mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions.
Relative atomic mass (average mass of one atom)/(mass of one atom of 12 C) x12
Carbon neutral No net carbon (dioxide) emissions to atmosphere
Hydration The addition of water to a molecule/compound.
Structural isomerism Compounds which have the same molecular formula but different structural formulae
Free radical Atom or molecule with an unpaired electron
Reducing agent A species that donates electrons
Ore A rock containing enough metal for extraction to be profitable
Oxidising agent A species that gains electrons in a redox reaction
Reduction Gain of electrons
Oxidation Loss of electrons
Disproportionation A redox reaction where some atoms of an element are oxidised and some atoms of the same element are reduced.
Empirical formula The simplest ratio of the number of atoms of each element in a compound
Molecular formula The number of atoms of each element in a molecule
First ionisation energy Energy needed to remove one mole of electrons from one mole of atoms in the gaseous state to form one mole of ions with a +1 charge
Atomic number The number of protons in the nucleus of an atom
Mass number Number of protons + number of neutrons
Rate of reaction Change in concentration of a substance / reactant / product per unit time
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