In general when we begin to study chemistry and we start writing equations we al
ID: 1031397 • Letter: I
Question
In general when we begin to study chemistry and we start writing equations we always use a single arrow (-->) which leads us to believe that reactions proceed in just one direction. That said we do encounter the two reactions below:
2H2 + O2 --> 2H2O
2H2O --> 2H2 + O2
What's the difference between the two? Just the direction of the arrow or what we start with and subsequently end up with - I could start with hydrogen and oxygen gas in a tube, add and igniter to generate a spark and end up with water or I could start with water, add an electric current and end up with hydrogen and oxygen gas.
So yes we then move into the discussion that many reactions are reversible in standard conditions. What we can't say is that all reactions are reversible - can you think of a common reaction that may not be reversible?
Explanation / Answer
Most reactions tend to be reversible under suitably designed conditions. However, it is our inability that we cannot study the reversible nature of most reactions due to the lack of suitable techniques.
The decomposition of calcium carbonate (CaCO3) to produce calcium oxide (CaO) and carbon dioxide (CO2) is a commonly studied reaction in lab. The reaction is reversible if carried out in a closed container. However, as most students do it, openly in the lab by heating CaCO3 in a crucible, the reaction tends to be irreversible.
CaCO3 (s) <======> CaO (s) + CO2 (g) (reversible in a closed container)
CaCO3 (s) --------------> CaO (s) + CO2 (g) (irreversible in an open container)
Another common experiment that all chemistry students perform in lab is a titration experiment, most notable titrating a strong acid (HCl) with a strong base (NaOH). The reaction goes to completion, producing sodium chloride (NaCl) and water (H2O), both neutral.
HCl (aq) + NaOH (aq) --------> NaCl (aq) + H2O (l)