CHAPTER 3. REACTION RATES 3.6
DEFINITION: A reversible reaction
A reversible reaction isa chemical reaction that can proceed in both
the forward and reversedirections. In other words, the reactant and
product of one reactionmay reverse roles.Activity: The reversibility of chemical reactions
Apparatus and materials:
Lime water (Ca(OH) 2 ); calcium carbonate (CaCO 3 ); hydrochloric acid; 2test
tubes with rubber stoppers; delivery tube; retort stand and clamp;Bunsen
burner.
Method and observations:- Half-fill a test tube with clear lime water (Ca(OH) 2 ).
- In another test tube, place a few pieces of calcium carbonate (CaCO 3 ) and
cover the pieces with dilute hydrochloric acid.Seal the test tube with a
rubber stopper and delivery tube. - Place the other endof the delivery tube intothe test tube containingthe
lime water so that the carbon dioxide that is produced from the reaction
between calcium carbonate and hydrochloric acid passes through the lime
water. Observe what happens to the appearance of the lime water. The
equation for the reactionthat takes place is:
Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O
CaCO 3 is insoluble and it turnsthe limewater milky. - Allow the reaction toproceed for a while so that carbon dioxide continues
to pass through the limewater. What do you notice? The equation for the
reaction that takes placeis:
CaCO 3 (s) + H 2 O + CO 2 → Ca(HCO 3 ) 2
In this reaction, calciumcarbonate becomes oneof the reactants to pro-
duce hydrogen carbonate (Ca(HCO 3 ) 2 ) and so the solution becomes clear
again.- Heat the solution inthe test tube over a Bunsen burner. What doyou
observe? You should see bubbles of carbon dioxide appear and the lime-
water turns milky again.The reaction that has taken place is:
Ca(HCO 3 ) 2 → CaCO 3 (s) + H 2 O + CO 2