First slide
Heat given
Question

Two moles of air, when heated through 10 K expands by an amount of 1.66 × 10–3 m3  under a constant pressure of 105 N/m2. If Cv = 20.81 J/mole K, then Cp is,

Moderate
Solution

\Delta W = P \times \Delta V = {10^5} \times 1.33 \times {10^{ - 3}}J

\Rightarrow \Delta W = 133J

\Delta U = n{C_V}\Delta T = 2 \times 20.81 \times 10J

\Rightarrow \Delta U = 416.2J

Now, \Delta Q = \Delta U + \Delta W

= (416.2+133)J

= 529.2 J

Also, \Delta Q = n{C_P}\Delta T

\therefore {C_P} = \frac{{\Delta Q}}{{n\Delta T}} = \frac{{549.2}}{{2 \times 10}}J/mol - K

= 27.46J/mol - K

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