Question

A process is carried out under constant pressure conditions. Given that for this process ΔH < 0 < ΔU, which of the following is true? Please Explain Answer

a. the system absorbs heat and expands during the process.

b. the system absorbs heat and contracts during the process.

c. the system loses heat and expands during the process.

d. the system loses heat and contracts during the process.

e. cannot be determined from the information given

Answer 1

H is less than zero it means system system releases heat.

and on the other hand U is greater than zero

we know U = W + Q (where Q = H for constant pressure conditions)

so U = W + H

so for U to be greater than zero W sholud be greater than zero

it means W > 0 which gives V < 0 (because W = - P V)

this implies that volume of system is decreasing means system contracts during the process.

So the system loses heat and contracts during the process. (answer D)