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The correct statement amongst the following is (1) ΔfH°298 is zero for O(g) (2) ΔfH°500 is zero for O2(g) (3) The term 'standard state' implies that the temperature is 0°C (4) The standard state of a pure gas is the pure gas at a pressure of 1 bar and temperature 273 K
- (1) ΔfH°298 is zero for O(g)
- (2) ΔfH°500 is zero for O2(g)
- (3) The term 'standard state' implies that the temperature is 0°C
- (4) The standard state of a pure gas is the pure gas at a pressure of 1 bar and temperature 273 K
Correct answer: (2) ΔfH°500 is zero for O2(g)
Solution
The standard enthalpy of formation (ΔfH°) for a substance in its standard state is defined as zero, but this is specifically true at 298 K for elements in their most stable form. However, the statement about ΔfH°500 being zero for O2(g) is misleading; it is not zero at that temperature, making it incorrect.
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