LS5_a - Unit 2 How do we analyze chemical change...

Chemistry XXI
Unit 2
How do we analyze
chemical change?
Understanding light

Chemistry XXI
Lab Session 5
How can we use light
to analyze a system?

Chemistry XXI
Your Challenge
You have been hired to provide the lighting for a
“ green ” building.
Your task is to rank the efficiency of available light
sources in terms of production of visible light
versus other types of radiation.
How can you determine efficiency of the
available light sources?

Chemistry XXI
Analyzing Light
Many systems emit light or “ electromagnetic
radiation ” when they interact with other systems
and undergo a physical or chemical change.
The nature of the
radiation that is
emitted can give us a
clue about the
properties of the
system or the changes
that are going on.

Chemistry XXI
Light Properties
The amount of energy provided by light,
or electromagnetic radiation , depends on the
wavelength or frequency of the radiation.
λ * ν = c
c = Speed of light =

Chemistry XXI
Electromagnetic Spectrum
Energy per photon
E = h • ν = h
• c/ λ
h = Planck’s constant =
When light and matter
interact, energy is
transmitted in packets of
energy called “ photons .”
Energy Increases

Chemistry XXI
Spectroscopy
A variety of powerful analytical techniques are
based on the analysis of the types and amount of
electromagnetic radiation absorbed or emitted by a
chemical substance ( Spectroscopies ).

Chemistry XXI
A spectrometer is an optical
instrument that allows us to
measure the amount of light
( number of photons ) as a
function of wavelength.