SCH 4U1 UNIT 4 EQUILIBRIUM

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

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

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

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

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)

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.

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

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.

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)

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.

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

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.

b) A balloon contains air and a few drops of water 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

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

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. 

Solutions to Worksheet Definitions a) closed system: a system that may exchange energy but not matter with its surroundings b) dynamic equil.: a balance between forward and reverse processes occurring at the same rate. c) chemical rxn equil: a dynamic equil between reactants and products of a chemical reaction in a closed system.

Solutions to Worksheet 2. a) example of solubility equil (dynamic equil between a solute and a solvent in a saturated soln in a closed system) I2 (s) ↔ I2 (aq) b) example of phase equilibrium (dynamic equilibrium between different physical states of pure substance in a closed system) - such as ice over a lake OR H2O (l) ↔ H2O (g)