Question

How much heat is required to heat 2 moles of a monoatomic ideal gas from 0${}^o$ C to 100${}^o$ C if no mechanical work is done during heating ? [ The specific heat of gas at constant pressure is 2.5 R, where R is the universal gas constant.]

• A. 378.6 cal
• B. 417.1 cal
• C. 596.4 cal
• D. 782 cal

Answer 1

Answer: (C)

596.4 cal

For no mechanical work to be done,
The process needs to be a constant volume process.
Given that:

$C_p=2.5R$

$C_p-C_v=R$

i.e. $C_v=1.5R$

Heat supplied is equal to

$Q=n{C}_v\Delta T=2\times 1.5R\times 100=300R=300\times 1.987=596.1cal$

Which is closest to option C.