Energetics — A/L Chemistry

What must I remember about Energetics?

• Enthalpy change (ΔH) represents heat exchanged at constant pressure: exothermic (ΔH < 0, heat released, products energetically more stable) and endothermic (ΔH > 0, heat absorbed).
• Standard enthalpy of formation (ΔH°_f) is the enthalpy change when 1 mole of a substance is formed from its constituent elements in their standard states (ΔH°_f of pure elements = 0).
• Hess's law states that overall enthalpy change is independent of the reaction pathway: ΔH°_reaction = ΣΔH°_f(products) - ΣΔH°_f(reactants).
• Bond dissociation enthalpy is the energy required to break 1 mole of gaseous bonds: ΔH_reaction = Σ(bonds broken in reactants) - Σ(bonds formed in products).
• Born-Haber cycles construct enthalpy cycles to determine the lattice energy of ionic solids using atomization, ionization, electron affinity, and dissociation energies.

Test yourself (1 minute)

1. Gibbs free energy equation

   ΔG = ΔH - TΔS. A process is spontaneous at constant T and P when ΔG < 0.

2. When ΔH < 0 and ΔS > 0

   reaction is spontaneous at all temperatures (ΔG is always negative).

3. Calorimetry formula

   q = mcΔT (where m is solution mass in g, c is specific heat capacity 4.18 J g⁻¹ K⁻¹ for aqueous solutions).

Practise Energetics questions today

Source: NIE G.C.E. (A/L) Chemistry Syllabus (Unit 5)

What should I study first?

What comes next?

Next in the syllabus

Where does Energetics fit in the syllabus?

Grade 12 · Term 2