1 / 9

HL5-6

Lattice Enthalpy 15.2.1. HL5-6.ppt. 15.2.1 – Define and apply the terms lattice enthalpy and electron affinity. Q – Which one of these are you already familiar with?. First ionization energy ( Δ H i ˚). Earlier we learned that metals and non-metals tend to form ionic compounds.

aurelia-hensley
Download Presentation

HL5-6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lattice Enthalpy 15.2.1 HL5-6.ppt

  2. 15.2.1 – Define and apply the terms lattice enthalpy and electron affinity. • Q – Which one of these are you already familiar with?

  3. First ionization energy (ΔHi˚) • Earlier we learned that metals and non-metals tend to form ionic compounds. • Q – Who loses and who gains electrons? • ΔHi˚ refers to the energy needed to form the positive ion. • Na(g)  Na+(g) + e-(g) ΔHi˚= +496 kJ/mol • Q – Why is this value >0? • Q – Which element would have a larger ΔHi˚ Na or Mg?

  4. First electron affinity (ΔHe˚) • On the other hand, the non-metal elements in ionic compounds attract electrons. • ΔHe˚ refers to the enthalpy change when one mole of gaseous atoms attracts one mole of electrons. • Values can be found in Table 7 of the IB Data Booklet. • Cl(g) + e-(g)  Cl-(g) ΔHe˚= -349 kJ/mol • Q – Is this process endo or exothermic?

  5. Lattice Enthalpies • So what if we put those two processes together? • Na(g) + Cl(g)  Na+(g) + Cl-(g) • ΔH˚= ΔHe˚ + ΔHi˚ = -349 + 496 = +147 kJ/mol • We can see that e- transfer process is endothermic, yet we know that the formation of salt is highly exothermic. Something else must be at play. • Q - In reality, what do those oppositely charged gas ions do?

  6. Lattice Enthalpies • The oppositely charged gas ions come together to form an ionic lattice (framework). • Q – Is this process endo or exothermic? • This process is highly exothermic as there is a strong attraction between the ions. • Na+(g) + Cl-(g)  NaCl(s) • ΔH˚= -790 kJ/mol • Generally, most endothermic reactions do not readily occur (like the transfer of electrons noted before) but this last step explains the readiness of metals and non-metals to form ionic compounds.

  7. Lattice Enthalpies • The lattice enthalpy ΔHlat˚ expresses this enthalpy change in terms of the reverse endothermic process. • It can also be described as the enthalpy related to the formation of gaseous ions from one mole of a solid crystal breaking into gaseous ions. • NaCl(s)  Na+(g) + Cl-(g) ΔHlat˚= +790 kJ/mol

  8. Review of ΔH variables • ΔH˚ = ? • ΔHlat˚ = ? • ΔHi˚ = ? • ΔHe˚ = ? • ΔHc˚ = ? • ΔHf˚ = ?

  9. HW • Work on your calorimetry IA

More Related