Experiment 7 Ch emical Properties of Compounds: Chemical Reactions Questions and

Question

Experiment 7 Ch emical Properties of Compounds: Chemical Reactions Questions and Problems (May be assigned before or after the experiment, depending on your instructor (Show all calculations where appropriate.) 1. Arom temperature white solid is mixed with a room temperature elear liquid rewalting n a dea.c d resulting in a clear,colorless liquid that is hot to the touch. Has a chemical reaction occurred? Why or why not 2. A clear, colorless liquid is mixed with a clear, blue liquid resulting in a white powder suspended in a clear, colorless liquid. Has a chemical reaction occurred? Why or why not?

Explanation / Answer

1. Release of heat when a substance dissolves in a liquid can either be a chemcal change which implies that an exothermic reaction has occured or the heat is produced due to exothermic dissolution of a compound. Common exothermic reactions involving solids added to liquids giving clear colourless hot solutions can be neutralization reactions. However, simply dissolving certain substances like NaOH, KOH and sodium carbonate in water also give a clear colourless liquid with release of heat. Thus without the knowledge about either the solid added or the liquid it is being added into, one cannot determine if a chemical reaction has occured by heat production.

Exothermic reactions produce heat because the products of the reactions have lesser energy than the reactants thus releasing the excess energy as heat. Exothermic dissolutions are so due to the higher stability of the solute in its dissolved state in the solvent thus liberating the heat locked up in the solute's solid state. Here the former alone is a chemica change while the latter is just a physical change.

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