If ∆H is the enthalpy change and ∆E the change in internal energy accompanying a gaseous reaction then:
Correct answer: D. ∆H is less than ∆E if the number of moles of gaseous products is less than the number of moles of gaseous reactants.
- A. ∆H is always less than ∆E .
- B. ∆H is always greater than ∆E .
- C. ∆H is less than ∆E if the number of moles of gaseous products is greater than the number of moles of gaseous reactants.
- D. ∆H is less than ∆E if the number of moles of gaseous products is less than the number of moles of gaseous reactants.
Explanation
As ∆H =∆E + ∆n0RT ∆H value is less than or greater than ∆E depending on the value of ∆ngwhich is the change in number of moles of the gaseous components. As result (a) and (b) cannot be true. ∆H<∆E when ∆n0< 0 , hence (c) is also false only (d) is correct.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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