Are these reactions Exothermic or Endothermic?
How do I know?
1.) Mg(OH)2(s)<==>Mg+2(aq) + 2OH-(aq)
Saw solution lighten from medium pink to very light when heated in hot water bath. (It had phenolphthalein drop for indicator.)
2.) HSO4-(aq)+ H2O(l)<==>H3O+(aq)+SO4-2
Saw solution (with thymol blu drop) turn to pale from dark pink when heated.
Thanks so much for any help.
To determine whether a reaction is exothermic or endothermic, you need to analyze the changes in energy during the reaction.
1.) Mg(OH)2(s) <==> Mg+2(aq) + 2OH-(aq)
In this reaction, you observed that the solution lightened from medium pink to very light when heated in a hot water bath. The presence of phenolphthalein as an indicator is important. Phenolphthalein is a pH indicator that changes color as the solution's pH changes. In this case, the solution initially had a basic pH due to the presence of hydroxide ions (OH-). When the reaction was heated, the hydroxide ions reacted with the magnesium ions (Mg+2) to form water (H2O). As a result, the concentration of hydroxide ions decreased, causing the solution to become less basic and resulting in the color change to a lighter shade. This reaction releasing energy as heat during the process, therefore, it is considered exothermic.
2.) HSO4-(aq) + H2O(l) <==> H3O+(aq) + SO4-2
In this reaction, you noted that the solution turned pale from dark pink when heated, with thymol blue as the indicator. Thymol blue is also a pH indicator that changes color based on pH. Initially, the solution had a low pH due to the presence of hydronium ions (H3O+). When heated, the hydronium ions reacted with the sulfate ions (SO4-2) to form sulfuric acid (HSO4-) and water (H2O). As a result, the concentration of hydronium ions decreased, causing a decrease in acidity and causing the solution to turn pale. This reaction also releases energy as heat during the process, making it an exothermic reaction.
In both cases, the color changes observed correspond to a decrease in the concentration of the respective ions present in the solution. This indicates that the reactions are releasing energy in the form of heat, making them exothermic reactions.