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Chemistry LibreTexts

Homework 28

  • Page ID
    28943
  • What wavelength of light in meters produces this amount of energy? Round to two significant figures.

    Formula for Energy is E=hc/lambda

    h is Planck's constant it is equivalent to 6.626 x 10-34

    c is the speed of light constant it is equivalent to 2.998 x 108

    lambda is the wavelength, which in this problem you are trying to find

    E is the energy which is what you will be given in this problem

    Examples:

    a) 1.33 x 10-19J

    1.33 x 10-19J =hc/lambda

    1.33 x 10-19 = (6.626 x 10-34)(2.998 x 108)/lambda

    1.33 x 10-19= 1.98 x 10-25/lambda

    1.33 x 10-19(lambda)= 1.986 x 10-25

    lambda =1.98 x 10-25/1.33 x 10-19

    lambda= 1.4936 x 10-6

    lambda = 1.5 x 10-6

    lambda = 1500 x 10 -9 m

    b) 3.98 x 10-19 J

    3.98 x 10-19J = hc/lambda

    3.98 x 10 -19 = (6.626 x 10-34)(2.998 x 108)/lambda

    3.98 x 10-19 = 1.986 x 10-25/lambda

    3.98 x 10-19(lambda) = 1.986 x 10-25

    lambda = 1.986 x 10-25/3.98 x 10-19

    lambda = 4.989 x 10-7

    lambda = 5.0 x 10-7

    lambda = 500 x 10-9 m

    c) 1.32 x 10-18J

    1.32 x 10-18J = hc/lambda

    1.32 x 10-18 = (6.626 x 10-34)(2.998 x 108)/lambda

    1.32 x 10-18 = 1.986 x 10-25/lambda

    1.32 x 10-18(lambda) = 1.986 x 10-25

    lambda = 1.5045 x 10-7

    lambda = 1.5 x 10-7

    lambda = 150 x 10-9 m

    Chapter 4 question:

    Which has the largest atomic radius in each pair?

    Atomic radius becomes larger going from top to bottom in each column.

    Atomic radius becomes smaller going left to right across the periodic table.

    If an atom in the first family (group 1) loses an electron, the atomic radius will become smaller.

    Examples:

    a) Cl or Fe

    Fe has the larger atomic radius

    b) Mg or B

    Mg has the larger atomic radius

    c) K+ or K

    K has the larger atomic radius

    d) Rb or Xe

    Rb has the larger atomic radius

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