Master essential A-Level Chemistry definitions, formulas, and application scenarios across Physical, Inorganic, and Organic disciplines.
25 cards
Front
State Hess’s Law.
Back
The total enthalpy change for a reaction is independent of the route taken. It allows indirect calculation of ΔH using energy cycles, usually involving combustion or formation data.
Front
Define Enthalpy Change of Formation (ΔHfθ).
Back
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions (298K, 100kPa). For elements, ΔHfθ = 0.
Front
Define Enthalpy Change of Combustion (ΔHcθ).
Back
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions. Always exothermic (negative).
Front
Calculate bond enthalpy for the reaction: N2(g) + 3H2(g) → 2NH3(g).
Back
ΔH = Σ(Bonds broken) - Σ(Bonds formed). Broken: N≡N + 3(H-H). Formed: 6(N-H). Calculation uses average values from a data table to find the energy change.
Front
Define relative atomic mass (Ar) and calculate it for an element with isotopes 35Cl (75%) and 37Cl (25%).
Back
Ar is the weighted average mass of an atom of an element relative to 1/12th the mass of a carbon-12 atom. Calculation: (0.75 × 35) + (0.25 × 37) = 26.25 + 9.25 = 35.5.
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