A sample of ideal gas `(gamma = 1.4)` is heated at constant pressure. If an amount `140 J` of heat is supplied to the gas, find (a) the changes in internal energy of the gas, (b) the work done by the gas.

Options

A. `25 J`
B. `40 J`
C. `35 J`
D. `20 J`

Answer

B

Explanation

Suppose the sample contains `n` moles. Also support the volume of changes from `V_(1)` to `V_(2)` and the temperature changes from `T_(1)` to `T_(2)`
The heat supplied is
`DeltaQ = DeltaU = PDeltaV = DeltaU+nRDeltaT = DeltaU+(2DeltaU)/(f)`
The change is internal energy is
`DeltaU = n f/2 R(T_2-T_1)=f/2 Rn(T_2-T_1)`
`(f)/(2+f) DeltaQ = (140J)/(1.4) = 100J`
The work done by the gas is
`DeltaW = DeltaQ-DeltaU = 140J-100J = 40J`.