Engineering Chemistry S Datta

560 ENGINEERING CHEMISTRY
Perception of color is by (a) additive and (b) subtractive processes.
In additive process perception of color is by mixing of primary colors, red, blue and
green. Combination of primary colors (two) gives secondary colors which again can be mixed to
give the full range of colors.
In subtractive process, pigments absorb certain colors and reflect back other colors. In
this process, the primary colors are magenta, yellow and blue-green. Each pigment absorbs
one primary color and reflects back the other two. Perception of color is quantitative and
subjective, it differs among individuals.
Highlights:
• The initial photon absorption gives rise to a short lived singlet state which
subsequently passes to long-lived triplet state, which actually participates in redox
chain.
• Photosynthesis involves a series of complex reactions with the overall conversion
of water and carbon dioxide to carbohydrates and dioxygen in the chloroplast.
EXERCISES
1. State: (a) Grotthurs-Drapper law (b) Stark-Einstein law.
2. Explain: (a) Franck-Condon principle.
3. Mention physical processes undergone by excited molecules.
4. What is energy cascade?
5. What are ISC and Photosensitizer?
6. Give examples of some photochemical reactions.
7. What is Norrish type I reaction? Give example.
8. Explain the chemistry of vision.
9. What are the Dark and Hill reactions?
10. Give a schematic representation of energy transduction in the noncyclic photosynthetic reaction
process.
11. Explain photosynthesis in the light of photochemical reactions.