Video Transcript
The diagram below shows the
experimental setup for a simple calorimeter to measure the enthalpy change in
certain reactions. For which type of reaction would
this experimental apparatus not be suitable for measuring the change in
enthalpy? (A) Dissolution, (B) combustion,
(C) displacement, (D) neutralization, or (E) precipitation.
A calorimeter is a device used for
measuring energy transferred as heat during physical or chemical changes. It can be considered an isolated
system where an isolated system is a system that does not allow for the transfer of
matter or energy with its surroundings. Now that we know what this setup is
used for, let’s look at the options from (A) to (E) to see which of these reaction
types this experimental apparatus would not be suitable for. Option (A) is dissolution. Dissolution occurs when a solute
dissolves in a liquid solvent. From the diagram, the reaction
mixture appears to be a liquid. As the solution involves a liquid
solvent, this apparatus would be suitable for dissolution.
Since the question asks “For which
type of reaction would this experimental apparatus not be suitable?” option (A) is
not the answer to this question. Option (B) is combustion. Combustion is burning. It involves reaction with
oxygen. Combustion reactions require
heat. But the polystyrene cup in this
setup is not a very good conductor of heat, and combustion requires a supply of
oxygen. But since the polystyrene cup has a
lid on it, the oxygen supply would be limited. So, combustion is unlikely to
occur, but if it did, it would produce a flame. But the polystyrene cup and cotton
wool are flammable, so this experimental apparatus would not be suitable for
combustion. Therefore, it seems like option (B)
combustion is the correct answer to this question. But to confirm, let’s look at
options (C) to (E).
Option (C) is displacement, which
is where a more reactive species displaces the less reactive species from its
compound. An example of this type of reaction
would be magnesium powder displacing copper in an aqueous copper sulfate
solution. Although displacement reactions can
occur between solid reactants, they usually take place in water, so this apparatus
is suitable for displacement. Thus, option (C) displacement is
not the answer to this question.
Option (D) is neutralization. Neutralization involves an acid
reacting with a base to produce a salt and water. The acid and base are usually
dissolved in water. In this case, the basic solution
may be referred to as an alkali, as an alkali is a soluble base. As in neutralization the reaction
mixture is a liquid, the experimental apparatus is suitable, so option (D) is not
the answer to this question.
Option (E) is precipitation. Precipitation reactions involve the
formation of an insoluble product from the combination of solutions. In these reactions, the solvent is
usually water, so this apparatus is suitable for precipitation. Thus, option (E) precipitation is
not the answer to this question. Therefore, the answer to the
question “For which type of reaction would this experimental apparatus not be
suitable for measuring the change in enthalpy?” is (B) combustion.
It should be noted that although
this simple calorimeter is not suitable for measuring the change in enthalpy for
combustion, a constant volume calorimeter or a combustion calorimeter would be
suitable.
