Question

old stars obtain part of their energy by the fusion of three alpha particles to form a 12/6c nucleus, whose mass is 12.0000 u. How much energy is given off in each such reaction?

Answer 1

Answer:

11.6532 x 10⁻¹¹ J or 7.3 MeV is given off

Explanation:

Mass of an alpha particle = 4.0026u,   ∴ mass of three = 12.0078u

Find the difference in mass.

Mass of three alpha - Mass of Carbon nucleus

12.0078u - 12u = 0.0078u

Since 1u = 1.66 x 10⁻²⁷ kg

Therefore, 0.0078u = 1.2948 x 10⁻²⁷

Now that we know Mass(m) = 1.2948 x 10⁻²⁷ and Speed (c) 3 x 10⁸ m²s⁻²

Formular for Energy ==> E₀ = mc²

E = (1.2948 x 10⁻²⁷) (3 x 10⁸ m²s⁻²)²

E = (1.2948 x 10⁻²⁷) (9 x 10¹⁶) J

E = 11.6532 x 10⁻¹¹ J

Or, if you need your energy in MeV

1 MeV = 1.60x10⁻¹³ J

Just do the conversion by dividing 11.6532 x 10⁻¹¹ J by 1.60x10⁻¹³ J

It will give you 7.3 MeV