Question

The combustion of palmitic acid is represented by the chemical equation: C16H3202(s) + 23 O2(g) → 16 CO2(g) + 16 H2O(1) The magnitude of A, U is in comparison to the magnitude of A,H a. The same b. Smaller c. Greater d. Need additional information

Please explain the answer thank you!

Answer 1

we know that   $\Delta$H = $\Delta$ U + $\Delta$ ng RT where H and U means enthalpy and internal energy respectively. and $\Delta$ ng = n(product) - n(reactant) now here is a condition that n should be number of moles of gaseous compound.

in this reaction we see only CO2 and O2 are gases. so their mole difference should be the $\Delta$ n

thus $\Delta$ H = $\Delta$ U + (16-23)RT = $\Delta$ U - 7RT that clearly indicate that enthalpy should be less than internal energy for this particular reaction.

that means $\Delta$ U is greater than $\Delta$ H.