Calculate ΔU and ΔH in calories if 1 mole of a monoatomic ideal gas is heated at constant pressure of 1 atm from 25oC to 50oC.
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Solution
For monoatomic ideal gas, Cv=32R
Cp=ΔHΔT
∴ΔH=CpΔTmol−1 ( or nCpΔT for n moles ) =52×1.987×25=124.2cal Work done, w=−PΔV=−P(V2−V1) =−(PV2−PV1)=−(nRT2−nRT1) =−mR(T2−T1) =−1×1.987(323−298)cal =−49.7cal ΔE=q+w =124.2−49.7cal=74.5cal.