Le Chatelier’s Principle: When a stress is applied to an equilibrium, the equilibrium will shift to alleviate the stress. Fe+3 (aq) + SCN-1 (aq) ⇋ FeSCN+2 (aq) Colorless Left shift = lighter color ⇋ Dark red Right shift = darker color Initial color Other ways to cause a Le Châtelier Shift: 3 H2 (g) + N2 (g) + heat ⇋ 2 NH3 (g) What kind of shift would you see if: Pressure increased? Right shift Volume increased? Left shift Heating temperature increased? Right shift CH4 (g) + 2 Cl2 (g) ⇋ CCl4 (g) + 2 H2 (g) + heat What kind of shift would you see if: Pressure increased? Heating temperature increased? No Change Left shift Indicators: • Indicators are organic dyes that are also weak acids or weak bases. • The color of the dye depends upon the pH of the solution. • The indicator will change colors at the pH that corresponds to its own equivalence point. • Therefore, it is important to pick an indicator that changes color very close to the pH at the equivalence point for the titration. • Since the color change does not exactly match the equivalence point, it is called the ENDPOINT of the titration.