A sample of ideal gas `(gamma = 1.4)` is heated at constant pressure. If an amount of 85 J of heat is supplied to gas, find `Delta U`.

Answer

9

Explanation

Gas is diatomic as `gamma = 1.4`, thus, `C_(V) = (5)/(2)R` and `C_(P) = (7)/(2)R`, Given, `Delta H = 85J` at constant pressure
Also, `Delta T (85)/(nC_(P)) = (140 xx 2)/(7 n xx R) = (40)/(n)`
Now,
`W = - nRT Delta T = - n xx 2 xx (40)/(n) = - 80 J`
Also, `q_(p) = DeltaH = Delta U + (-W)`
`Delta U = Delta H + W = 85 - 80`
`Delta U = 5J`