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Equilibria seminar. University of Lincoln presentation. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License. Le Chatelier’s Principle.

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  1. Equilibria seminar University of Lincoln presentation This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  2. Le Chatelier’s Principle When an external change is made to a system in equilibrium, the system will respond to oppose the change 1. BiCl3(aq) + H2O(l) ↔ BiOCl(s) + 2HCl(aq) 2. Cr2O72-(aq) + 2OH-(aq) ↔ 2CrO42-(aq) + H2O(l) How does reaction 1 respond to addition of hydrochloric acid? How does reaction 2 respond to addition of alkali? How does reaction 2 respond to addition of acid? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  3. N2(g) + 3H2(g) ↔ 2NH3(g) CO(g) + 2H2(g) ↔ CH3OH(g) 2NO2(g) ↔ 2NO(g) + O2(g) PCl5(g) ↔ PCl3(g) + Cl2(g) H2(g) + I2(g) ↔ 2HI(g) CO(g) + H2O(g) ↔ CO2(g) + H2(g) How do the above equilibria respond to: An increase in pressure A decrease in pressure This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  4. N2(g) + 3H2(g) ↔ 2NH3(g) rH = -92.2 kJ mol-1 H2(g) + I2(g) ↔ 2HI(g) rH = -9.4 kJ mol-1 CO(g) + H2O(g) ↔ CO2(g) + H2(g) rH = -41.2 kJ mol-1 PCl5(g) ↔ PCl3(g) + Cl2(g) rH = 87.9 kJ mol-1 How do the above respond to an Increase in temperature Decrease in temperature This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  5. pKa= 4.77 • CH3COOH (aq) + H2O(l)↔ H3O+ (aq) + CH3COO- (aq) • CH3COOH: CH3COO- at pH = 4.77 ? • CH3COOH: CH3COO- at pH = 3 ? • CH3COOH: CH3COO- at pH = 7 ? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  6. CH3NH2(aq) +H2O(l)↔ CH3NH3+(aq) + OH-(aq) pKa = 10.66 (of conjugate acid) pH = 10.66 [B]=[BH+] pH =8 what happens to CH3NH3+(aq): CH3NH2(aq) pH =13 ? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  7. Acidic drugs ibuprofen How does this molecule ionise? pKa=4.5 pH =3 (stomach pH)? pH=6 (intestine)? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  8. Basic drugs amphetamine (C6H5CH2CH(NH2)CH3) Write an equation for the reaction of amphetamine with water. The pKa of the conjugate acid is 9.8. What will happen to the ratio of ionised to unionised amphetamine at: pH 7 pH 12 Why might this be important? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  9. Making a buffer solution • Choose a weak acid with a pKa close to the required pH of the buffer. • Choose an appropriate salt of the weak acid • Determine [salt]/[acid] ratio needed to give correct pH • What would be the pH of an ethanoate buffer with equal acid and sodium ethanoate concentrations? This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  10. pKa values (data tables) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  11. Ethanoate buffers pH = 5 pH = 4 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

  12. Acknowledgements • JISC • HEA • Centre for Educational Research and Development • School of natural and applied sciences • School of Journalism • SirenFM • http://tango.freedesktop.org This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

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