AP Ch 14 Equilibrium

AP Ch 14 Equilibrium - Chemical Equilibrium Chapter 14...

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Chemical Equilibrium Chapter 14
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Equilibrium: the extent of a reaction In stoichiometry we talk about theoretical yields, and the many reasons actual yields may be lower. Another critical reason actual yields may be lower is the reversibility of chemical reactions: some reactions may produce only 70% of the product you may calculate they ought to produce. Equilibrium looks at the extent of a chemical reaction.
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Equilibrium is a state in which there are no observable changes as time goes by. Chemical equilibrium is achieved when: the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant Physical equilibrium H 2 O ( l ) Chemical equilibrium N 2 O 4 ( g ) 14.1 H 2 O ( g ) 2NO 2 ( g )
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Rate of sale of Rate of sale of cookies cookies = = Rate of replacing Rate of replacing cookies cookies
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The Concept of Equilibrium The Concept of Equilibrium Consider colorless frozen N 2 O 4 . At room temperature, it decomposes to brown NO 2 : N 2 O 4 ( g ) 2NO 2 ( g ). At some time, the color stops changing and we have a mixture of N 2 O 4 and NO 2 . Chemical equilibrium is the point at which the rate of the forward reaction is equal to the rate of the reverse reaction. At that point, the concentrations of all species are constant. Using the collision model: – as the amount of NO 2 builds up, there is a chance that two NO 2 molecules will collide to form N 2 O 4 . – At the beginning of the reaction, there is no NO 2 so the reverse reaction (2NO 2 ( g ) N 2 O 4 ( g )) does not occur.
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The Concept of Equilibrium The Concept of Equilibrium As the substance warms it begins to decompose: N 2 O 4 ( g ) 2NO 2 ( g ) When enough NO 2 is formed, it can react to form N 2 O 4 : 2NO 2 ( g ) N 2 O 4 ( g ). At equilibrium, as much N 2 O 4 reacts to form NO 2 as NO 2 reacts to re-form N 2 O 4 The double arrow implies the process is dynamic. N 2 O 4 ( g ) 2NO 2 ( g )
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The Concept of Equilibrium The Concept of Equilibrium As the reaction progresses [A] decreases to a constant, [B] increases from zero to a constant. When [A] and [B] are constant, equilibrium is achieved. A B
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N 2 O 4 ( g ) 2NO 2 ( g ) Start with NO 2 Start with N 2 O 4 Start with NO 2 & N 2 O 4 equilibrium equilibrium equilibrium 14.1
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14.1 constant
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The Equilibrium Constant The Equilibrium Constant No matter the starting composition of reactants and products, the same ratio of concentrations is achieved at equilibrium. For a general reaction the equilibrium constant expression is where K c is the equilibrium constant.
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This note was uploaded on 05/25/2010 for the course CHEM 101 taught by Professor Fricke during the Spring '10 term at Canisius College.

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AP Ch 14 Equilibrium - Chemical Equilibrium Chapter 14...

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