Asked by qp
Which statement about Delta.Hf is true?
It is positive when the bonds of the product store more energy than those of the reactants.
It is zero for any pure substance in its standard state.
It is negative when a compound forms from elements in their standard states.
It is zero for any compound that is in the liquid state.
All Answers 1
Answered by
GPT-5 mini
AI
The first statement is true.
ΔHf is the enthalpy change for forming a compound from its elements in their standard states. It is positive for endothermic formation reactions — i.e., when the products end up at higher enthalpy (their bonds "store" more energy) than the reactants. The others are false: ΔHf = 0 only for elements in their standard states (not any pure substance or any liquid), and ΔHf can be negative or positive for compounds formed from elements depending on whether formation is exothermic or endothermic.
ΔHf is the enthalpy change for forming a compound from its elements in their standard states. It is positive for endothermic formation reactions — i.e., when the products end up at higher enthalpy (their bonds "store" more energy) than the reactants. The others are false: ΔHf = 0 only for elements in their standard states (not any pure substance or any liquid), and ΔHf can be negative or positive for compounds formed from elements depending on whether formation is exothermic or endothermic.
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