Lava at T_H = ~725 degree C emerges from a volcano. A mass m = 85 kg of this lav

Question

Lava at T_H = ~725 degree C emerges from a volcano. A mass m = 85 kg of this lava flows at a constant velocity of v = 0.27 m/s losing Q = 16750 J of heat every second to the surroundings. The lava flows a distance of 250 m before reaching the ocean. Assume that the temperature of the surroundings, T?surr = 27 degree C is unaffected by the cooling of the lava. Calculate how long t in seconds it takes before this mass of lava reaches the ocean. t = Calculate the amount of heat Q_l in joules lost to the surroundings before this mass reaches the ocean. If the specific heat capacity of the lava in this process is c = 840 J/kg degree C. calculate the temperature of this mass of lava T in Celsius just before it reaches the ocean. Calculate entropy change of the surroundings delta S_surr in J/K while the lava was moving toward the ocean. Calculate the change in the entropy of the lava delta S in joules per kelvin while the lava was moving toward the ocean. Did the cooling of the lava before it reached the ocean violate the second law of thermodynamics?

Explanation / Answer

Part (a) : Time taken is given by -

we know that, t = d / v = (250 m) / (0.27 m/s)

t = 926 sec

Part (b) :

Q = heat lost per second = 16750 J

t = time = 926 sec

Ql = Q t = 16750 x 926 = 1.55 x 107 J

c)

T = temperature as it reach the ocean

m = mass = 85 kg

c = specific heat = 840 J/kgC

using the formula

Ql = m c (Th - T)

1.55 x 107 = (85) (840) (725 - T)

T = 507.91 C

Related Questions

Navigate

• Browse (All)
• Browse L
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.