Question

Without doing any detailed calculation, specify for each process whether each of the following quantities is positive, negative or equal to zero: q, w, ∆U, ∆S, ∆Ssurr. Provide a brief explanation for each of your choices. If the question does not allow you to come to a definite conclusion, briefly discuss the possibilities.

(a) A sample of water is boiled at 100◦C and 1.00 atm.

(b)A sample of an ideal gas expands irreversibly and adiabatically into a vacuum.

(c) A sample of gas is heated at constant pressure

(d) A sample of gas expands reversibly at constant temperature.

Answer 1

a) ∆T = 0, isothermal. q= +, w= - , ∆U = 0, ∆S = ∆q/T = + , ∆S surr = -

b) Adiabatic, q = 0, w = +, ∆U = -, ∆S = 0, ∆S Surr = 0

c) ∆P = 0, Isobaric, q= +, w = +, ∆U = +/-, ∆S = +, ∆ S surr = -

d) ∆ T , isothermal, q = 0, w = +, ∆ U = -, ∆ S = 0, ∆ S surr = 0