The correct statement amongst the following is:

(A) The term 'standard state' implies that the temperature is 0°C

(B) The standard state of pure gas is the pure gas at a pressure of 1 bar and temperature 273 K

(C) $\Delta_f H^\circ_{298}$ is zero for O(g)

(D) $\Delta_f H^\circ_{500}$ is zero for $\ce{O2(g)}$

Question

The correct statement amongst the following is:

(A) The term 'standard state' implies that the temperature is 0°C

(B) The standard state of pure gas is the pure gas at a pressure of 1 bar and temperature 273 K

(C) $\Delta_f H^\circ_{298}$ is zero for O(g)

(D) $\Delta_f H^\circ_{500}$ is zero for $\ce{O2(g)}$

Paaras Thakur · Accepted Answer

D only. 🧠 Standard enthalpy of formation is zero for elements in their standard reference state — at ANY temperature "Standard state" specifies 1 bar pressure but not a fixed temperature. The reference temperature is arbitrary (often 298 K, but f H can be defined at any T). For any element in its most stable form at that pressure and temperature, f H = 0 by definition. Evaluating statements: - (A) False — standard state does not require 0°C. - (B) False — standard state specifies 1 bar but does not require 273 K. - (C) False — O(g) is an atom, not the standard form of oxygen. The standard state is O2(g), so f H(O(g)) 0. - (D) True — O2(g) is the standard reference form of oxygen at any temperature. Answer: (d)

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A only

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B only

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C only

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D only

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