Question

For which of the following substances ΔfH° is not zero
(a) Ca (s)
(b) He (g)
(c) P (red)
(d) CH₃OH (I)

Answer 1

Answer:

(D) CH OH (l)

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Explanation:

Ok friends

Answer 2

Answer:

For CH₃OH (I) the ΔfH° is not zero i.e.option(d).

Explanation:

• The enthalpy change that occurs when one mole of a compound is created from its constituent parts in their most stable state of aggregation is known as the standard enthalpy of formation (stable state of aggregation at temperature: 298.15 K, pressure: 1 atm).

• The state of an element that makes it most stable at 1 bar of pressure.
• One exception is phosphorus, where red phosphorus is chosen as the conventional reference state for zero enthalpies of formation despite the fact that black phosphorus is the most stable form of the element at 1 bar.
• Since there is no change involved in the formation of any element in its standard state (for example, oxygen gas, solid carbon in the form of graphite, etc.), all elements have a standard enthalpy of formation of zero.
• Ca, He(g), and P( red ) are found in their standard states. So, their standard enthalpy of formation is zero.
• CH₃OH (l) is formed from a sequence of chemical reactions. So, the heat of formation is not zero.

For CH₃OH (I) the ΔfH° is not zero i.e.option(d).

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