Unformatted text preview: Name: Tasfia Ahmed Chem 10, Section: 1411 Prelab Assignment: Chemical Equilibrium and Le Chatelier’s Principle
1. Consider the reversible reaction: A + B ' C + D a. What happens to the forward and reverse reaction rates when equilibrium is achieved? When equilibrium is achieved the rate of the forward reaction is equal to the
rate of the backward reaction.
b. What happens to the reactant (A and B) and product (C and D) concentrations when equilibrium is achieved? When equilibrium is achieved both the forward and backward reactions still occur, but the
concentrations of A, B C and D remain constant
2. Le Chatelier's Principle states that if a stress is applied to a reversible reaction at equilibrium, the reaction will
undergo a shift in order to re-establish its equilibrium. Consider the following exothermic reversible reaction
2A ' B + C
In which direction (left or right) would the following stresses cause the system to shift?
a. decrease the concentration of A left b. increase the concentration of B right c. lower the temperature right 3. In this lab you will explore the effect of Le Chatelier's Principle on several chemical systems at equilibrium.
These are supplied on page 2 of the Theory Section. Consider the third system you will study: the Aqueous
a. Write the balanced equation for this reversible reaction. NH3 (aq) + H2O (l) NH4+1 (aq) + OH-1 (aq)
b. Suppose you added some excess ammonium ions to this system at equilibrium.
-- In which direction would a shift occur?
-- What color change might you expect to observe? left no color change since ammonia solutions
are colorless 4. List all the equipment you will use in this lab. 10 small test tubes, test tube rack, test tube holder, Bunsen burner, 2 medium-sized
beakers (for stock solutions), 10-mL graduated cylinder, wash bottle, stirring rod, and
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