Question

For which of the following substances $\Delta fH{}^\circ $ is not zero.
A.$C{{a}_{(s)}}$
B.$H{{e}_{(g)}}$
C.${{P}_{(red)}}$
D.$C{{H}_{3}}O{{H}_{(l)}}$

Answer 1

Hint: We know that here in this problem to know which equation is suitable for the formation of methanol we have to find out first the equation where all the constitutes are in their standard state .In the standard state, the heat of formation of constitutes is zero.

Complete answer:
We can say that heat of formation is the quantity of heat absorbed (or) released when one mole of a compound is produced from its fundamental elements, each substance being in its regular physical state such as gas, solid, (or) liquid. We have to know that the formation reactant is a process at constant temperature and constant pressure.
The formation of methanol and we can easily calculate the heat of formation here because in the rest of the option it is not possible to calculate heat of formation because either the constituents are not in their standard state or the equation is not balanced. Graphite and diamond are the allotropes of carbon .The structure of graphite and diamond are simple hexagonal and face-centered cubic respectively. But graphite is the most stable form of carbon under standard conditions.
We can call heat of formation as standard heat of formation, standard enthalpy of formation. We have to know that standard enthalpy of formation for any element present in its standard state takes a value of zero. This is because there is no change taking place in their formation.

Therefore, the correct answer is option D.

Note:
Remember that synthetically methanol can be prepared by heating by carbon monoxide and hydrogen gases under pressure in the presence of a catalyst and the reaction must contain all the constituents in their standard form. The reaction that takes place in the formation of methanol.