Equilibrium Chemical Physical

Closed system Dynamic equilibrium OUTCOME QUESTION(S): C12-4-04 EQUILIBRIUM AND Keq Relate the concept of equilibrium to physical and chemical systems. Include: conditions necessary to achieve equilibrium. Write equilibrium law expressions from balanced chemical equations and solve problems involving equilibrium constants. Include: ICE tables Vocabulary & Concepts Closed system Dynamic equilibrium

FEW reactions end with NO reactants and 100% product * Kinetics applies to the rate of a reaction. 2 Na (aq) + Cl2 (aq) 2 NaCl (aq) 2 H2O (g) O2 (g) + 2 H2 (g) FEW reactions end with NO reactants and 100% product ex·tent (ikˈstent/): the degree, size or scale of something. In this case – how much product can be made? Many products can collide and “reform” reactants: these reactions are called “reversible” * Equilibrium applies to the extent of a reaction.

aA + bB cC + dD Concentration Kinetic Region Equilibrium Region Consider the Collision Theory: Can you explain why the concentrations plateau? Reactants Products teqbm Time

Which situation is likely to reach equilibrium? Why? Equilibrium will only be reached with: A reversible reaction Sealed container Constant condition ([ ], T, P, V) closed system H2O (l) H2O (g) Which situation is likely to reach equilibrium? Why? Physical equilibrium: Reversible physical process, where rate of forward process is equal to rate of reverse process.

“Dynamic equilibrium” Liquid – Vapour Physical Equilibrium: Kinetic: molecules vapourize filling the space. As more molecules vapourize, it becomes more likely for molecules to condense. Equilibrium: evaporation rate = condensation rate. Amounts of each stay constant (plateau) VAPOUR “Dynamic equilibrium” changing balance Macroscopically nothing appears to be changing BUT microscopically molecules are in flux. LIQUID

Solubility equilibrium is only reached with a saturated solution Solubility Physical Equilibrium: Kinetic: molecules dissolve filling the space. As more solute dissolves, it becomes more likely for molecules to precipitate. Equilibrium: dissolving rate = precipitation rate. Amounts of each stay constant (plateau) SOLVENT Solubility equilibrium is only reached with a saturated solution C6H12O6(s) C6H12O6(aq) SOLUTE

How is it different? How is it the same? Other examples of physical equilibria include: Vapour Pressure Solid - Liquid (held at melting point) Liquid - Vapour (held at boiling point) The interaction of smog with the sun is an example of Chemical Equilibrium: How is it different? How is it the same? Photochemical smog smog 2 NO2 (g) N2O4 (g)

2 NO2 (g) N2O4 (g) Photochemical smog Chemical Equilibrium: Photochemical smog smog 2 NO2 (g) N2O4 (g) Kinetic: molecules convert to colourless variant. As more molecules react, it becomes more likely for molecules of the reverse process to react. Equilibrium: forward rate = reverse rate. Concentrations of each stay constant (plateau) The winter cold increases the conversion to colourless (pollution looks less in winter – but it’s just invisible)

Constant macroscopic properties Chemical equilibrium: Reversible chemical process, where concentrations of reactants and products remain constant over time because the rates of the forward reaction equal the reverse reaction. Constant macroscopic properties At equilibrium (te): Rate of forward reaction EQUALS rate of reverse reaction – indefinitely. 2. Concentrations of both reactants and products will be CONSTANT – not same, but constant.

aA + bB cC + dD Concentration Rate Kinetic Region Equilibrium Region Kinetic Region Equilibrium Region Concentration Rate Reactants Reactants Products Products teqbm teqbm Time Time Notice that the time equilibrium is reached is the same for both graphs: the concentrations plateau because the forward and reverse rate are occurring at the same pace

Closed system Dynamic equilibrium CAN YOU / HAVE YOU? C12-4-04 EQUILIBRIUM AND Keq Relate the concept of equilibrium to physical and chemical systems. Include: conditions necessary to achieve equilibrium. Write equilibrium law expressions from balanced chemical equations and solve problems involving equilibrium constants. Include: ICE tables Vocabulary & Concepts Closed system Dynamic equilibrium