Calculate the change in internal energy when `5g` of air is heated from internal energy when `5g` of air is heated from `0^(@)C "to" 2^(@)C`. Specific heat of air at constant volume is `0.172 cal//g//^(@)C`.

Explanation

Here, `dU=?m= 5g, DeltaT= 2^(@)C`
`C_(v)= 0.172 cal//g//^(@)C`
`dQ=mC_(v) DeltaT= 5xx10.172xx2 cal`
`=1.72xx4.2J= 7.2J`
As air is heated at constant volume,
`:. dW= 0`
From first law of thermodynamics,
`dU+dW=dQ`
`dU=dQ-dW= 7.2-0= 7.2J`