chempresentation1

chempresentation1 - Chapter 7: Chemical Systems In Chapter...

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Chapter 7: Chemical Systems In
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Chapter 7.1:  Dynamic  Equilibrium in  Chemical Systems
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What is a Closed a System? A system that may exchange energy but not matter with its surroundings. What does it mean when we say a closed system is in dynamic equilibrium? This means that in a closed system a balance is achieved by apposing processes occurring at the same rate. Example: A bottle of carbonated soft drink is a closed system, there no change until the bottle is opened. The closed bottle displays constant macroscopic properties . When the cap is removed the pressure on the system is reduced and carbon dioxide bubbles come out of the solution. Several macroscopic properties remain constant; liquid continues to look clear, colourless and bubble-free and the gas above the liquid continues to appear colourless and transparent. The level of the liquid does not change, since macroscopic properties remain constant, these opposing changes occur at equal rates. Represented by: CO 2(g) CO 2(aq)
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Explanation of Representation: Equation with double arrows shows that the change occurs both ways Characteristic of a System at Equilibrium The forward rate = The reverse rate The reactant and product concentrations are constant The Macroscopic (observable) properties are constant The system is dynamic as the forward and reverse reactions continue The equilibrium can be approached form starting with reactants or starting with products Reverse Reaction : in the equilibrium equation the right–to-left reaction Forward Reaction : in the equilibrium equation the left-to-right reaction Conditions Necessary for Equilibrium Closed system Constant Temperature Ea is low so the reaction is reversible
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Types of Equilibrium 1) Solubility Equilibrium A dynamic equilibrium between a solute and a solvent in a saturated closed system Equilibrium is reached when the solute ions dissolve and crystallize at the same rate. 2) Phase Equilibrium A dynamic equilibrium between different physical states of a pure substance in a closed system Evaporation/ condensation phase equilibrium -the rates at which the molecules are evaporating and condensing become equal: Equilibrium is formed Solid/liquid phase equilibrium -when the temperature is at 0 °C the melting point and freezing point are equal: Equilibrium is formed
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A dynamic equilibrium between reactants and products of a chemical reaction in a closed system Example: CaCO 3(s) CaO (s) + CO 2(g) heat In open system quantitative reaction so equilibrium does not occur CaCO 3(s) CaO (s) + CO 2(g) In closed system both reactants and products present. Reaction is no longer quantitative: explained by effect of the reverse reaction CaCO 3(s) CaO(s) + CO 2(g) The final state of a chemical system at equilibriums can be explained as a competition between collisions of reactants to form products and collisions of products to form reactants. Both reactants and products are present after a reaction is stopped (it isn’t
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chempresentation1 - Chapter 7: Chemical Systems In Chapter...

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