enthalpy Flashcards
(18 cards)
What are the standard conditions in thermochemistry?
Temperature 298 K (25°C), Concentration 1 mol dm⁻³, Pressure 1 atm (101 kPa)
What is the standard state of a substance
The physical state of a substance under standard conditions (e.g. CO₂ gas, H₂O liquid, NaCl solid)
What is the standard enthalpy change of formation (ΔHᶠ°)
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states
Write the equation for the standard enthalpy of formation of NaCl
Na(s) + ½Cl₂(g) → NaCl(s), ΔHᶠ° = –411.15 kJ mol⁻¹
What is the standard enthalpy change of atomisation (ΔHᵃᵗ°)
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Write the equation for the atomisation of sodium
Na(s) → Na(g), ΔHᵃᵗ° = +107.32 kJ mol⁻¹
What is 1st ionisation energy (ΔHᴵᴱ°)
Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms
Write the equation for the 1st ionisation of sodium
Na(g) → Na⁺(g) + e⁻, ΔHᴵᴱ° = +498.3 kJ mol⁻¹
What is 1st electron affinity (ΔHᴱᴬ°)
Enthalpy change when 1 mole of gaseous atoms gain electrons to form 1 mole of 1⁻ ions
Write the equation for the electron affinity of chlorine
Cl(g) + e⁻ → Cl⁻(g), ΔHᴱᴬ° = –346 kJ mol⁻¹
What is the standard enthalpy change of solution (ΔHˢᵒˡ°)
Enthalpy change when 1 mole of a compound dissolves in water under standard conditions
Write the equation for the solution of NaCl
NaCl(s) → Na⁺(aq) + Cl⁻(aq), ΔHˢᵒˡ° = +4 kJ mol⁻¹
What is the standard enthalpy of hydration (ΔHʰʸᵈ°)
Enthalpy change when 1 mole of aqueous ions form from gaseous ions under standard conditions
Write the hydration equations for Na⁺ and Cl⁻
Na⁺(g) → Na⁺(aq), ΔHʰʸᵈ° = –420 kJ mol⁻¹; Cl⁻(g) → Cl⁻(aq), ΔHʰʸᵈ° = –363 kJ mol⁻¹
State Hess’s Law
The enthalpy change of a reaction is the same regardless of the route taken
What is the enthalpy change of reaction (ΔHʳ°)
The enthalpy change when the substances in a given equation react under standard conditions
What is the standard enthalpy change of combustion (ΔHᶜ°)
The enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions
