Question

Plutonium isotopes undergo decay, producing heat. Plutonium isotope 239 (Pu-239) has 1.9 watts per kilogram [W/kg] of decay heat. How much heat, in units of calories [cal], will 1.25 moles [mol] of Pu-239 release after decaying for three hours [h]

Answer 1

Answer:

1495.81 calories = 1500 calories to 2 s.f

Explanation:

1.9 Watts of decay heat is released for every kilogram of Pu-239 that decays.

1.25 moles of Pu-239 will release which amount of heat in 3 hours (calories)

First of, we calculate how much mass of Pu-239 is contained in 1.25 moles of Pu-239.

Molar mass of Pu-239 = 244 g/mol = 0.244 kg/mol

1.25 moles of Pu-239 = 1.25 × 0.244 = 0.305 kg

1 kg of Pu-239 is equivalent 1.9 Watts

0.305 kg of Pu-239 will give (0.305×1.9/1) Watts; 0.5795 Watts.

Note: Watts is J/s

Power = Energy/time

Energy = power × time

Power = 0.5795 Watts

Time = 3 hours = 3×3600 s = 10800 s

Energy = 0.5795 × 10800 = 6258.6 J

1 J = 0.239 calorie

6258.6 J = 6258.6 × 0.239 = 1495.81 calories