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Which process, occurring at atmospheric pressure, would you expect to have a positive enthalpy change, ΔH?

#chemistry #pressure #enthalpy

a. dry ice subliming

b. the combustion of gasoline in your car's engine

c. ice forming on a plane's windshield

d. the reaction in a hot pack used by a cold fan at a football game

Answers (1)

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A positive ΔH means that heat is being absorbed. Heat is often required to break bonds or cause phase changes to occur.

The sublimation of solid CO2 to form gaseous CO2 has a positive ΔH

The burning of gasoline gives off heat, ΔH is negative. The same is true for the formation of ice from liquid water or water vapor, heat is given off. Clearly a "hot pack" is giving off heat and is exothermic with a negative ΔH.

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