Question

When 1 mol of a fuel burns at constant pressure, it exchanges-3452 kJ of heat and does-11 kJ of workon the surroundings. What are ΔUand ΔH for the combustion of thisfuel?

Answer 1

Answer:-3463 kJ and -3452kJ

Explanation:

ΔU is the change in internal energy of a system and its formula is;

ΔU = q + w

Where q represents heat transferred into or out of the system. Its value is positive when heat is transfer into the system and negative when heat is produced by the system.

W represents the work done on or by the system. Its value is positive when work is done on the system and negative when it is done by the system.

For the system in this question, we see that it produces heat which means heat is transferred out of the system, therefore the value of q is negative, it can also be seen that work is done by the system which means that w is also negative.

Therefore,

ΔU = -q-w

ΔU = -3452 kJ – 11kJ

= - 3463kJ

ΔH is the change in the enthalpy of a system and its formuls is;

ΔH = ΔU + Δ(PV)

By product rule Δ(PV) becomes ΔPV + PΔV

At constant pressure ΔP = 0. Therefore,

ΔH = -q-w + PΔV

w is equals to PΔV, So:

ΔH = -q

ΔH = -3452kJ