Equilibrium and Stress

1. Equilibrium and Stress Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. Resources Available • Exp. L: Equilibrium and Stress

3. Fe(NO3)3 NH4SCN KSCN NaNO3 H2SO4 CuSO4 Co(NO3)2 Observations What color was observed for each compound? Each compound breaks into one type of positive ion (cation) and one type of negative ion. What ions are formed?

4. Observations Which ions are responsible for color?

5. Concentration Effects Thiocyanatoiron(III) Ion System

6. Write a balanced molecular equation for this reaction. Write a balanced ionic equation for this reaction. Write a balanced net ionic equation for this reaction.

7. What species is responsible for the red color?

8. Fe3+(aq) + SCN-(aq) [FeSCN]2+ Q = Thiocyanatoiron(III) Ion Equilibrium Mass-Action Expression [[FeSCN]2+] [products] [Fe3+] [reactants] [SCN-] Write the mass-action expression for the formation of the thiocyanatoiron(III) ion.

10. Q = Fe3+(aq) + SCN-(aq) [FeSCN]2+ [[FeSCN]2+] [products] ? = K [FeSCN]2+ + Fe(NO3)3 [Fe3+] [reactants] [SCN-] What does a darker red color indicate? What ions are added when Fe(NO3)3 is added to the solution? Why does the solution turn a darker red color?

11. Q = Fe3+(aq) + SCN-(aq) [FeSCN]2+ [[FeSCN]2+] [products] ? = K [FeSCN]2+ + KSCN [Fe3+] [reactants] [SCN-] What ions are added when KSCN is added to the solution? Why does the solution turn a darker red color?

12. Q = Fe3+(aq) + SCN-(aq) [FeSCN]2+ [[FeSCN]2+] [products] ? = K [FeSCN]2+ + NH4SCN [Fe3+] [reactants] [SCN-] Why does the solution turn a darker red color?

13. Q = Fe3+(aq) Fe3+(aq) + EDTA(aq) + SCN-(aq) [FeEDTA]- + 4 H+(aq) [FeSCN]2+ [[FeSCN]2+] [products] [FeSCN]2+ + EDTA [Fe3+] [reactants] [SCN-] Why does the solution turn a lighter red color?

14. Q = Fe3+(aq) + SCN-(aq) [FeSCN]2+ [[FeSCN]2+] [products] [FeSCN]2+ + water [Fe3+] [reactants] [SCN-] Why does the solution turn a lighter red color? Does the equilibrium shift?

16. Pressure Effects Nitrogen Dioxide-Dinitrogen Tetroxide System

17. NO2(g) + NO2(g) N2O4(g) O O O O N N N N O O O O Nitrogen Dioxide - Dinitrogen Tetroxide

18. NO2(g) + NO2(g) N2O4(g) Nitrogen Dioxide - Dinitrogen Tetroxide 0 sec 1 sec 10 sec

19. NO2(g) + NO2(g) N2O4(g) P ( P )2 NO2 N2O4 Q = Nitrogen Dioxide - Dinitrogen TetroxideMass-Action Expression [products] [reactants] Why does the gas initially get darker and then lighten?

20. Dilution Effects Tetrachlorocuprate(II) Ion

21. Cu2+(aq) + 4 Cl-(aq) [CuCl4]2- Tetrachlorocuprate(II) Ion Which ion is responsible for the color in each solution?

22. Cu2+(aq) + 4 Cl-(aq) [CuCl4]2- Tetrachlorocuprate(II) Ion and Water top view Deionized water causes the pale blue color, salt water gives a pale green solution.

23. Cu2+(aq) + 4 Cl-(aq) [CuCl4]2- Q = Tetrachlorocuprate(II) Ion Equilibrium Mass-Action Expression [[CuCl4]2-] [products] [Cu2+] [reactants] [Cl-]4 Why does the addition of water change the solution color, but the addition of salt water have no effect?

24. Temperature Effects Nitrogen Dioxide-Dinitrogen Tetroxide Tetrachlorocobaltate(II) Ion

25. NO2(g) + NO2(g) N2O4(g) Nitrogen Dioxide - Dinitrogen Tetroxide Is the equilibrium reaction endothermic or exothermic? ice water room temp hot water

26. NO2(g) + NO2(g) N2O4(g) P ( P )2 NO2 N2O4 Q = Nitrogen Dioxide - Dinitrogen TetroxideMass-Action Expression Why does the color change?

27. Co2+(aq) + 4 Cl-(aq) [CoCl4]2- Tetrachlorocobaltate(II) Ion Which ion is responsible for the blue ion?

28. Co2+(aq) + 4 Cl-(aq) [CoCl4]2- [[CoCl4]2-] K = [Co2+] [Cl-]4 Tetrachlorocobaltate(II) Ion Equilibrium Mass-Action Expression pink cobalt blue When the solution is heated, is the equilibrium constant increasing or decreasing?