In this problem, we will try to understand why chemical reactions cannot power the Sun, but nuclear reactions can. The energy scale of chemical reactions is a few eV, where eV is a unit of energy called an electron volt. 1 eV = 1.602 x 10-19 J.  A typical chemical reaction involves an energy change of ~0.1 to 10 eV. In contrast, a nuclear reaction typically involves a change in energy of order a few MeV (mega electron volts; a factor of a million larger). Suppose that the Sun has a constant luminosity throughout its life, equal to its current luminosity of L⊙=3.827×1026J/s . Suppose also that the Sun is made entirely of hydrogen (or just protons, since the mass of the electron is about 2000 times smaller and is negligible in comparison). If every pair of two protons in the Sun undergo a one-time chemical reaction that nets ~1 eV of energy, how long would it take (in years) to expend all the available chemical energy?

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In this problem, we will try to understand why chemical reactions cannot power the Sun, but nuclear reactions can. The energy scale of chemical reactions is a few eV, where eV is a unit of energy called an electron volt. 1 eV = 1.602 x 10-19 J.  A typical chemical reaction involves an energy change of ~0.1 to 10 eV. In contrast, a nuclear reaction typically involves a change in energy of order a few MeV (mega electron volts; a factor of a million larger).

Suppose that the Sun has a constant luminosity throughout its life, equal to its current luminosity of L⊙=3.827×1026J/s . Suppose also that the Sun is made entirely of hydrogen (or just protons, since the mass of the electron is about 2000 times smaller and is negligible in comparison). If every pair of two protons in the Sun undergo a one-time chemical reaction that nets ~1 eV of energy, how long would it take (in years) to expend all the available chemical energy?

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