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Born Haber Cycles and Enthalpy

Born Haber Cycles and Enthalpy. 24/10/13. Energy Changes. First Law of Thermodynamics states that energy is always conserved. For a chemical reaction, the reaction mixture is referred to as the System. Everything else (test tube, surrounding air etc ) is referred to as the Surroundings.

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Born Haber Cycles and Enthalpy

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  1. Born Haber Cycles and Enthalpy 24/10/13

  2. Energy Changes • First Law of Thermodynamics states that energy is always conserved. • For a chemical reaction, the reaction mixture is referred to as the System. • Everything else (test tube, surrounding air etc) is referred to as the Surroundings. • The Enthalpy change for a reaction is the energy exchanged with the surroundings at constant pressure.

  3. Symbol for standard enthalpy change is ΔHᶱ • Some definitions: • Standard enthalpy of atomisation • Standard enthalpy of formation • Hess’s Law: the total enthalpy change involved in a chemical change is independent of the route by which the change takes place.

  4. In order to compare enthalpies, we look at values calculated at standard conditions. • Standard conditions are: • 1 atmosphere pressure • 298 K • Reagents in their normal state at standard conditions • For solutions, 1M solutions are standard

  5. Born Haber Cycles • Used to calculate the theoretical values for lattice energies (as they cannot be measured directly) • Calculate the lattice energy (KJmol⁻¹) for NaCl • Calculate the lattice energy for MgCl₂ • Calculate the lattice energy for MgO

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