Question

a vessel contains helium which expands at constant pressure when 15kj of heat is supplied to it what will be the change in internal energy of the gas

Answer 1

Q = heat energy supplied = 15 kJ

ΔT = change in temperature

n = number of moles of the gas

ΔU = internal energy change

at constant pressure , heat supplied is given as

Q = n Cp ΔT                                    eq-1

internal energy change is given as

ΔU = n Cv ΔT                                  eq-2

dividing eq-1 by eq-2

Q/ΔU = (n Cp ΔT) /(n Cv ΔT)

Q/ΔU = Cp /Cv

we know that for a mono atomic gas like helium, Cp /Cv = 5/3

hence

Q/ΔU = 5/3

inserting the value of heat energy

15/ΔU = 5/3

ΔU = 9 kJ