Question

The work done in open vessel at 300K, when 112g iron reacts with HCl to give \[FeC{l_2}\], is nearly:
A.- 1.2 kcal
B.0.6 kcal
C.- 0.3 kcal
D.– 0.2 kcal

Answer 1

The reaction between Fe and HCl is exothermic in nature, i.e. it releases energy in the form of heat.
Formula Used:
\[\] \[\dfrac{{mass}}{{molar mass}}\]

Complete step by step answer:
We know that the molar mass of iron is 56 g/mol. Hence, we can calculate the number of moles of iron present in the given sample, which weighs 112g:
\[No.{\text{ }}of{\text{ }}moles{\text{ }}of{\text{ }}iron{\text{ }} = \] \[\dfrac{{mass}}{{molar mass}}\]
                    \[ = \dfrac{{112}}{{56}}\]
                     = 2 moles
Therefore, 2 moles of iron are present in the given sample.
For the given setup, where the work done in open vessel at 300K, we can calculate the work done using the following formula:
Work done = \[P\vartriangle V\]
But according to ideal gas equation, we can say that,
PV = nRT
Where P is the pressure of the experimental setup, V is the volume, n is the number of moles, R is the Gas constant and T is the Temperature.
Hence, we can say that,
Work done = nRT
Now substituting the values of n = 2 mols; R = 2 cal/K.mol; and T = 300K, we get
Work done = (2) (2)(300) = 1200 cal
This can also be written as 1.2 kcal
Since, this reaction results in the formation of \[FeC{l_2}\], energy is released from iron during bond formation which is equivalent to the heat energy absorbed.
Hence for the system, the heat is lost and the value of work done is of negative magnitude.

Hence, Option A is the correct option.

Note:
The observations obtained from experiments may be recorded in different units. Also, there may be certain experiments that may be using different derived elements to obtain similar results. In accordance to the conditions and the units in any experiment or observation, the units and values of the gas constant also changes. The value of R must be chosen in accordance to the units of the given data.