The temperature of 20 g of oxygen gas is raised from `50^(@)C` to `100^(@)C`. (ii) At constant pressure. Find out the amount of heat supplied and the rise in internal energy in case.
Given , `R = 2 cal cdot mol^(-1) cdot K^(-1)` , for oxygen, `c_(v) = 0.155 cal cdot g^(-1) cdot^(@)C^(-1)`.

Explanation

Oxygen may be taken as an ideal gas. Internal energy is a function of temperature only.
So, the rise in internal energy at constant pressure will be the same, i.e., `U_(f) - U_(i) = 155 cal = 651 J`.
`C_(v) = Mc_(v) = 0.155 xx 32 = 4.96 cal cdot mol^(-1) cdot K^(-1)`
[M = molecular mass of oxygen = 32]
`:. C_(p) = C_(v) + R = 4.96 + 2 = 6.96 cal cdot mol^(-1) cdot K^(-1)`
20 g oxygen = `20/32` mol oxygen
`:.` Heat supplied at constant pressure,
`= 20/32 xx 6.96 xx (100 - 50)`
`=217.5 cal.`