AS Chemistry Definitions List Keyword Definition Activation Minimum energy (1) Energy required before a reaction can occur or go or start (1) Atomic number Number of protons in one atom or nucleus (1) Allow protons & electrons do not allow protons + electrons or electrons 1 Catalyst A substance that speeds up the reaction / alters the rate but is chemically unchanged at the end / not used up Both ideas needed Dynamic Rate of forward reaction = rate backward reaction (1) Equilibrium concentration remains constant (1) NOT Allow same’ if clear that ‘Equal’, ‘The means constant 2 Electronegativity Tendency or strength or ability or of an atom/element/nucleus to attract/withdraw electrons / e– density / bonding pair / shared pair 1 In a covalent bond (tied to M1 unless silly slip in M1) – (If molecule/ion then = CE = 0) (NOT electron (singular) for M1) Mark as 2 + 2 1 Empirical (simplest) ratio of atoms of each element in compound (1) Formula Enthalpy Heat energy change (1) Change Not energy on its own measured at constant pressure (1) Mark separately, ignore constant temperature statements 2 First Ionisation Enthalpy/energy change/required when an electron is Energy removed/ knocked out / displaced/ to form a ion (ignore energy)1 ‘minimum’ from a gaseous atom (could get M2 from a correct equation here) (accept change for ‘Enthalpy/energy the process...’ followed by an appropriate equation, for both marks) (accept molar definitions)1 Hess’s Law. (The enthalpy change for a reaction is) independent of the route (1) Isotope with the same number of protons / proton number (1) NOT same atomic number
AS Chemistry Definitions List Keyword Definition Activation Energy Minimum energy (1) required before a reaction can occur or go or start (1) Atomic number Number of protons in one atom or nucleus (1) Allow protons & electrons do not allow protons + electrons or electrons 1 Catalyst A substance that speeds up the reaction / alters the rate but is chemically unchanged at the end / not used up Both ideas needed Dynamic Equilibrium Rate of forward reaction = rate backward reaction (1) concentration remains constant (1) NOT ‘Equal’, Allow ‘The same’ if clear that means constant 2 Electronegativity Tendency or strength or ability or of an atom/element/nucleus to attract/withdraw electrons / e– density / bonding pair / shared pair 1 In a covalent bond (tied to M1 – unless silly slip in M1) (If molecule/ion then = CE = 0) (NOT electron (singular) for M1) Mark as 2 + 2 1 Empirical Formula (simplest) ratio of atoms of each element in compound (1) Enthalpy Change Heat energy change (1) Not energy on its own measured at constant pressure (1) Mark separately, ignore constant temperature statements 2 First Ionisation Energy Enthalpy/energy change/required when an electron is removed/ knocked out / displaced/ to form a ion (ignore ‘minimum’ energy)1 from a gaseous atom (could get M2 from a correct equation here) (accept ‘Enthalpy/energy change for the process...’ followed by an appropriate equation, for both marks) (accept molar definitions)1 Hess’s Law. (The enthalpy change for a reaction is) independent of the route (1) Isotope with the same number of protons / proton number (1) NOT same atomic number
as_chemistry_definitions_list_wt.docx