Types of Energy

(1) Kinetic Energy (Ek) : Translational, Vibrational and Rotational K.E.
     Ek = (1/2)mv2          Translational K.E.

Eg > Find a kinetic energy of a person (70kg)  walking at a speed of 1m/s.
     Ek = (1/2)(70kg)(1m/s)2 = 35 J


(2) Potential Energy(Ep):  (Force x Distance)

        [A] Gravitational Potential Energy

 Ep = (mg) (h) = mgh       in a gravitational force field
        g = 9.807 m/s2

 Eg. >  Find a gravitational potential energy of an apple (300g)
          which is  4.0 m above the ground in the tree.

       Ep = mgh  = (0.300 kg) (9.807 m/s2) (4.0m) = 11.8 kg  m2/s2 ~ 12 J

     [B] Electrostatic Potential Energy

Energy required when two charged particles are brought to the distance from an infinite distance.

 Ep = (kQ1Q2/r2)(r) = kQ1Q2/r     in electrostatic field
                Coulomb's Law
        k = 8.99 x 109 J m/C2

Eg. >  Find an  electrostatic potential energy of a Na ion and a Cl ion in NaCl crystal in which the interionic distance is 282 pm.

 Ep =  kQ1Q2/r
     = (8.99 x 109 J m/C2 )(1.602x10-19C)(- 1.602x10-19C)/(282x10-12m)
     = - 8.18x10-19 J

For one mole of NaCl:
 Ep = (-8.18x10-19 J)(6.022x1023/mol) = -493 kJ/mol

(The minus sign means energy is released when two ions are brought to a distance of 282pm from an infinite distance.)

In other words, 493 kJ is required in order to separate 1 mols of all Na+ ions and Cl- ions apart.



(3) Radiant Energy of an Electromagnetic Wave (EMW):       c=λ ν

      E=hν= hc/λ     where, h=6.626 x 10-34 J s
                             c=2.998 x 108 m/s

  Eg. > Find an energy of 1 mol of red light with a wavelength of 680nm.

       E = (6.626 x 10-34 J s)(2.998 x 108 m/s)/(680 10-9m) x (6.022 x 1023/mol)
          = (2.921 x 10-19 J) x (6.022 x 10-23) =   175,920 J = 176 kJ/mol


(4) Electrical Energy:   (Power x Time)

     E = i V t = p t

  Eg> Find energy consumed when a 40 watts light bulb is turned on for 1hour.
            E = (40J/s)(1 hr)(3600s/hr) = 144,000J = 144kJ


(5) Mass Energy
     E = mc2                where, c=2.998 x 108 m/s

 Eg > During every second the Sun burns and transforms 700 M tons of H to 695 M tons of He.    5 M tons of mass are converted to energy every second in the nuclear fusion reaction.

(a) Find the power of the Sun.
(b) How much energy the Sun generate in a day?

(a)  E = m c2 = (5x106x103kg) x (2.998 x 108 m/s)2
             =  4.5 x 1026 kg m2/s2 = 4.5 x 1026 J = 4.5 x 1023 kJ

       Power = Energy/time =  4.5 x 1023 kJ/1s = 4.5 x 1026 Watts

(b)   (4.5 x 1026J/s) (3600s/hr)(24hrs/day) = 3.88 x 1031J/day
                                                                   ~ 4 x 1028 kJ/day

Cf. Annual World Energy Consumption:        4 x 1017 kJ/yr  (400 EJ/yr)

Internal Energy:

 Sum of the kinetic and potential energies of all particle in a system