SCH 4U1 UNIT 4 EQUILIBRIUM

1. SCH 4U1UNIT 4EQUILIBRIUM

2. Prior Knowledge Q’s: • Negative enthalpy change indicates an reaction. • Positive enthalpy change indicates an reaction. exothermic endothermic

3. Prior Knowledge Q’s: • Which line represents an endothermic reaction (blue or green)? • Blue=exothermic • Green= endothermic

4. Prior Knowledge Q’s: • In words, describe what a rate of a reaction is rate of reaction: the change in the amount of reactants or products over time

5. Prior Knowledge Q’s: • Using the previous definition, write an equation for the rate of reaction: rate of reaction = Δ [A] Δt Note: [A] is the concentration of either the reactants or the products

6. LESSON 1:INTRODUCTION TO EQUILIBRIUM A+B → AB + energy This symbol means that >99% of the product AB is formed. (Spontaneous rxn) AB + energy → no reaction Therefore, in the opposite direction <1% of AB reacts. (Non-spontaneous)

7. What is EQUILIBRIUM? • At equilibrium, reactions actually take place in both the forward and reverse directions at the same time. These reactions can be shown together using a double arrow, A + B ↔ AB Note: Equilibrium is not equalibrium. The amount of products and reactants is not necessarily equal.

8. Equilibrium Mini Lab • Transfer of water using straws between two graduated cylinders: cylinder A starting volume = 10mL cylinder B starting volume = 0mL

9. Mini Lab Results - Equilibrium does not mean equal volume (equal concentration). When the experimental system is at equilibrium, the volumes are different. - Chemical equilibrium is reached when the proportion of reactants and products stays constant.

10. An Example of Equilibrium • A sealed flask containing water will contain a mixture of liquid and vapour water that will eventually establish a stable or balanced condition known as equilibrium. H2O (l) ↔ H2O (g)

11. Characteristics of a System at Equilibrium • The system is closed. • The rate of the forward reaction equals the rate of the reverse reaction. • The concentrations of the reactants and products are constant. • The temperature and pressure remains constant. • The same equilibrium state can be reached by starting with reactants or products.

12. STEADY STATE SYSTEMS • Steady states should not be confused with equilibrium states • These states appear to be in equilibrium but in reality they are not • A steady state is an irreversible process occurring in an open system in which input of energy and materials equals the output of energy and materials. bathtub example

13. Which of the following systems constitute steady-state situations, and which are at equilibrium? For each, a constant property is indicated. • An open pan of water is boiling on a stove. The temperature of water is constant. Steady State - not an equilibrium; in order for equilibrium to exist, the system must be closed.

14. b) A balloon contains air and a few drops of water. The pressure in the balloon is constant. equilibrium c) A Bunsen burner burns in a laboratory to give a well-defined flame. Supplies of gas and air are constant. steady state

15. d) The liquid mercury in a thermometer and the mercury vapour above it in a closed thermometer at constant temperature. equilibrium e) A plant manufacturing CaO from CaO3 by the reaction CaO3  CaO + CO2. The plant produces 200 tonnes of CaO each day. steady state

16. Check your understanding When a chemical system is in equilibrium, a number of items are true:  1.  The rates of the forward and reverse reactions are_________.  2.  The concentrations of all the substances involved are _________.  3.  This happens because the products and reactants are being formed __________.  4.  There will be both ____________present but the concentrations of them will not necessarily be equal.