Lab 9 - Equilibrium and Le Châtelier's Principle

Lab 9 - Equilibrium and Le Châtelier's Principle - Lab 9...

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4/15/13 Lab 9 - Equilibrium and Le Châtelier's Principle www.webassign.net/ebooks/wsugencheml1/lab_9/manual.html 1/5 Contents > Lab 9 - Equilibrium and Le Châtelier's Principle Lab 9 - Equilibrium and Le Châtelier's Principle Purpose To observe systems at equilibrium, and to determine what happens when stresses are applied to such systems. Goals To observe the effect on equilibrium of adding or removing products and reactants. To predict the direction in which the equilibrium shifts upon a change in concentration of one of the components. To determine the thermicity of a reaction based on equilibrium shifts. Introduction Many chemical systems are considered to be reversible. For example, drop the temperature of water to 0°C and it freezes; raise the temperature above 0°C and it melts. Many chemical reactions are also reversible. If one mixes ammonia and oxygen, the products form according to equation 1: ( 1 ) 4 NH 3 ( g ) + 3 O 2 ( g ) → 2 N 2 ( g ) + 6 H 2 O( g ) Conversely, a mixture of nitrogen and water, under the right conditions, can give ammonia and oxygen: ( 2 ) 2 N 2 ( g ) + 6 H 2 O( g ) → 4 NH 3 ( g ) + 3 O 2 ( g ) Perhaps unsurprisingly, in either case one actually obtains a mixture of all four gases. A reaction in which the reactants are not completely consumed to form products because the reverse reaction also occurs (products form reactants) is a reversible reaction . Such reactions are indicated by the use of double arrows as shown in equation 3: ( 3 ) 4 NH 3 ( g ) + 3 O 2 ( g ) 2 N 2 ( g ) + 6 H 2 O( g ) In dealing with equilibrium reactions, several definitions are useful and are given below.
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4/15/13 Lab 9 - Equilibrium and Le Châtelier's Principle www.webassign.net/ebooks/wsugencheml1/lab_9/manual.html 2/5 Products are the chemical species to the right of the equilibrium arrow, as the reaction equation is written. Reactants are the chemical species to the left of the equilibrium arrow, as the reaction equation is written. The forward reaction is the process as written from left to right in the reaction equation. The reverse reaction is the process as written from right to left in the reaction equation. In mixtures of the sort shown in equation 3 4 NH 3 ( g ) + 3 O 2 ( g ) 2 N 2 ( g ) + 6 H 2 O( g ) , products are constantly being transformed to reactants and vice versa. When the rate of the forward reaction is equal to the rate of the reverse reaction, the amounts of the chemical species remain constant, and the system is in a state of equilibrium . Anything that changes a variable associated with the equilibrium induces a
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