Question

What is the mass of chlorine in 3.9 x 1019 molecules of Cl2?

Answer 1

Explanation:

A photon is a quantum of EM radiation. Its energy is given by E = hf and is related to the frequency f and wavelength λ of the radiation by

E=hf=hcλ(energy of a photon)E=hf=hcλ(energy of a photon),

where E is the energy of a single photon and c is the speed of light. When working with small systems, energy in eV is often useful. Note that Planck’s constant in these units is h = 4.14 × 10−15 eV · s.

Since many wavelengths are stated in nanometers (nm), it is also useful to know that hc = 1240 eV · nm.

These will make many calculations a little easier.

All EM radiation is composed of photons. Figure 1 shows various divisions of the EM spectrum plotted against wavelength, frequency, and photon energy. Previously in this book, photon characteristics were alluded to in the discussion of some of the characteristics of UV, x rays, and γ rays, the first of which start with frequencies just above violet in the visible spectrum. It was noted that these types of EM radiation have characteristics much different than visible light. We can now see that such properties arise because photon energy is larger at high frequencies.