Answer to Question #145423 in General Chemistry for Renzon San Pedro

Question

2. For each of the following processes deduce whether each of the quantities q, w, U, and H is positive, zero, or negative.
a. Reversible melting of solid benzene at 1 atm and the normal melting point.
b. Reversible melting of ice at 1 atm and 0 °C
c. Reversible heating of a perfect gas at constant P
d. Reversible cooling of a perfect gas at constant V
e. Reversible adiabatic expansion of a perfecta gas in a vacuum,

Answer 1

a. Therefore,

q = positive (heat has to absorbed for benzene to melt)

w = negative (expansion during melting)

∆U = positive (internal energy increases)

∆H = positive (because heat is absorbed)

b. Therefore,

q = positive (heat has to absorbed for water to melt)

w = positive (water compresses during melting)

∆U = positive (internal energy increases)

∆H = positive (because heat is absorbed)

c. Therefore,

q = positive (heat is absorbed)

w = negative (the gas expands during heating to maintain constant pressure)

∆U = positive (internal energy increases)

∆H = positive (because heat is absorbed)

d. Therefore,

q = negative (heat is released)

w = zer (gas volume is constant)

∆U = negative (internal energy decreases)

∆H = negative (because heat is released)

e. Therefore,

q = 0 (adiabatic, no heat exchange)

w = negative (the gas expands during heating to maintain constant pressure)

∆U = negative (internal energy reduces as volume increases)

∆H = positive (because volume increases (∆H = ∆U + p∆V))