Remember Conservation of Energy: Energy is not created or destroyed. It is converted form one form to another.
Mechanical Energy Conversion: G.P.E. into Kinetic Energy and Kinetic Energy into G.P.E.
Mechanical Energy into Heat
Chemical Energy Conversions:
C +O2 --> C O2 + 95kcal/mole of C (Heat)
1 calorie = 4.186 Joules, Therefore we get (95kcal/mole)*(4.186J/cal)
= 397kJ/mole of C Heat Energy
(Note: 1mol = 6.02 * 1023 ) The molecular weight of Carbon is 12. Which means that 1 mole of Carbon = 12 grams. Therefore there is 397kJ of heat energy released for every 12 grams of carbon burned
The chemical reaction of burning carbon converts chemical potential energy into heat.
Other Reactions
2H2 + O2 --> 2H2O + 68kcal/mole of H2
Converting we find that there is 284kJ/mole of heat energy released in this reaction.
H2 is Hydrogen.. The molecular weight of Hydrogen molecule H2 is 2. Which means that 1 mole of H2 = 2 grams. Therefore there is 284kJ of heat energy released for every 2 grams of hydrogen gas burned. Compared with Carbon where we have 397kJ/12grams = 33kJ/gram, Hydrogen gas we have 284kJ/2 grams = 142kJ/gram a factor of 4 greater. When hydrogen reacts with oxygen you get heat. A more potent explosion than burning carbon.
Electrical Energy:
Voltage is a measurement of the amount of energy that is available to a charged particle such as an electron. The basic unit of charge is called the coulomb. The basic unit for voltage is the VOLT. 1VOLT = 1 Joule /coulomb. An electron has a charge of -1.6 * 10-19 coulombs. The potential energy of a charged particle such as an electron can be calculated Electrical Energy = qÆV where q is the amount of charge and ÆV is the available potential change. An electron that interacts with a potential change of 1volt has an energy of:
( 1.6 * 10-19 Coul)(1 Joule/Coul) = 1.6 * 10-19 Joules
This amount of energy is also called the electron-volt
1ev = 1.6 * 10-19 Joules
We will study electricity further and will get a better understanding. For now, there is an Electrical Potential Energy that causes electrons to gain kinetic energy. This kinetic energy is transformed into heat or light that use every minute of everyday.
Mass Energy:
E = Æmc2
When a nuclear reaction occurs there is some missing mass. This missing mass is converted into energy.
The missing mass when Uranium 235 fissions (splits apart) results in an energy of approximately 200Mev/nucleus. How does that compare with the burning of Carbon and Hydrogen in kJ/gram?
This is a good exercise in conversion factors, canceling units and calculating while we learn something.
We have 6.02 * 1023 nuclei in a mole of Uranium 235. The energy/mole =
(6.02 * 1023 nuclei/mole)(200 MeV/nuclei) = (1204* 1023)MeV/mole
1ev = 1.6 * 10-19 Joules
(1204* 1023)MeV/mole * 1.6 * 10-19 Joules/eV = 1926 * 104 MJ/mole =
1.926 * 1010 kJ/mole of Uranium 235 1 mole of Uranium 235 has a mass of 235 grams. Therefore
1.926 * 1010 kJ/mole / 235 g/mole = 8.20 * 107 kJ/gram