Question

U₁ , q, w, U₂ are given. U is internal energy, q is absorbed heat, w is work done and U₂ is final energy. 

(a) Derive an equation for ∆U. 

(b) Give the equation for w. 

(c) Calculate the change in internal energy of a system which absorbs 200 J of heat and 315 J of work is done by the system.

Answer 1

(a) U₂ = U₁ + q +w 

U₂ – U₁ = q + w 

or ∆U = q + w 

(b) w= -p∆V

(c) q = 200J 

w = -315J 

∆U = ? 

∆U = q + w 

= 200 + {315} 

= 200 - 315 = -115J