Question

The value of ∆H for cooling 2 moles of an ideal mono atomic gas from 125°C to 25°C at constant pressure will be [given C_P = \(\frac{5}{2}\) R] ……

(a) -250 R 

(b) -500 R 

(c) 500 R 

(d) +250 R

Answer 1

(b) -500 R

T_i = 125°C = 398K 

T_f = 25°C = 298 K 

∆H = nC_p (T_f – T_i ) 

∆H = 2 x \(\frac{5}{2}\) R(298 – 398) 

∆H = -500 R