Answer: Comparison of Energy Released per Gram of Fuel.

Chapter 43, Problem 43.47

(choose chapter or problem)

Comparison of Energy Released per Gram of Fuel. (a) When gasoline is burned, it releases 1.3 * 108 J of energy per gallon (3.788 L). Given that the density of gasoline is 737 kg>m3 , express the quantity of energy released in J>g of fuel. (b) During fission, when a neutron is absorbed by a 235U nucleus, about 200 MeV of energy is released for each nucleus that undergoes fission. Express this quantity in J>g of fuel. (c) In the proton-proton chain that takes place in stars like our sun, the overall fusion reaction can be summarized as six protons fusing to form one 4 He nucleus with two leftover protons and the liberation of 26.7 MeV of energy. The fuel is the six protons. Express the energy produced here in units of J>g of fuel. Notice the huge difference between the two forms of nuclear energy, on the one hand, and the chemical energy from gasoline, on the other. (d) Our sun produces energy at a measured rate of 3.86 * 1026 W. If its mass of 1.99 * 1030 kg were all gasoline, how long could it last before consuming all its fuel (Historical note: Before the discovery of nuclear fusion and the vast amounts of energy it releases, scientists were confused. They knew that the earth was at least many millions of years old, but could not explain how the sun could survive that long if its energy came from chemical burning.)