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.

Explanation

`gamma=1.4`,`P:`constant
`C_V=(5R)/(2)`,`C_P=(7R)/(2)`
`(DeltaQ)_P=nC_PDeltaT=140J`
(a) `DeltaU=nC_VDeltaT`
`(DeltaU)/(DeltaQ)=(C_V)/(C_P)=(1)/(gamma)`
`DeltaU=(DeltaQ)/(gamma)=(140)/(1.4)=100J`
(b) `DeltaW=(DeltaQ)_P-DeltaU=140-100=40J`
`DeltaW=nRDeltaT`
`(DeltaW)/((DeltaQ)_P)=(R)/(C_P)=(R)/((7R)/(2))=(2)/(7)`
`DeltaW=(2)/(7)(DeltaQ)_P=(2)/(7)xx140=40J`