Questions and Answers
The wavelength of visible light is defined as being between 400 to 800 nm.
True
Photochemistry studies chemical reactions that occur without the absorption of electromagnetic radiation.
False
When a molecule absorbs electromagnetic radiation, it is promoted to a lower electronic state.
False
Planck's constant is equal to 6.63 x 10^-34 Js.
Signup and view all the answers
The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength.
Signup and view all the answers
An Einstein refers to the energy of one mole of photons, which is 6.02 x 10^23 photons.
Signup and view all the answers
A photophysical process involves both energy transfer and product formation.
Signup and view all the answers
Electromagnetic radiation can be absorbed only by a limited number of organic molecules based on their specific energies.
Signup and view all the answers
What initiates all photochemical and photophysical processes?
Signup and view all the answers
According to Beer-Lambert's Law, what does the symbol ε represent?
Signup and view all the answers
What is the relationship between absorbance (A), concentration (c), and path length (l) as described by the Beer-Lambert law?
Signup and view all the answers
In the equation log(Iout/Iin) = -εcl, what does Iout represent?
Signup and view all the answers
How does path length (l) affect absorbance (A) according to the Beer-Lambert law?
Signup and view all the answers
What happens to intensity of light as it passes through an absorbing substance according to the Beer-Lambert law?
Signup and view all the answers
Study Notes
Photochemistry
- Branch of chemistry involving chemical reactions triggered by absorption of electromagnetic radiation
- Involves absorption of light in visible (400-800 nm) and ultraviolet (200-400 nm) regions
Electronic Excitation
- Molecules get activated due to electronic excitation when absorbing electromagnetic radiation
- Involves promotion of an electron from bonding molecular orbital to antibonding molecular orbital
Quantum Theory
- Both matter and light are quantized
- Specific organic molecules absorb specific energies of light for excitation
Photons
- Energy transfer occurs through photons, which have both wave and particle-like properties
- Energy (E) of a photon is given by Planck's law: E = hv
- Where h is Planck's constant (6.63 x 10^-34Js) and v is the frequency of oscillation
- v is related to wavelength (λ) by: v = c/λ, where c is the velocity of light
- Therefore, E = hv = hc/λ, showing energy is proportional to frequency and inversely proportional to wavelength
Energy Units
- Energy of one mole of photons (6.02 x 10^23 photons) is called an Einstein
- Measured in units of kJ mol^-1
Types of Photochemical Processes
- Photo physical process: energy transfer only
- Photochemical process: product formation
Absorption of Light
- Photochemical and photophysical processes start with the absorption of light or ultraviolet radiation, leading to an electronically excited state.
Beer-Lambert's Law
- The extent of absorption varies greatly between substances, with the probability of absorption indicated by the molar absorption coefficient (ε).
- The intensity of light entering a substance (Iin) is greater than the intensity of the emerging light (Iout).
- There is an exponential relationship between the relative absorption (Iout/ Iin) and the concentration (c) and path length (l) of the absorbing substance: Iout/ Iin = 10^(-ecl).
- Taking logarithms to the base 10 gives: log (Iout/ Iin) = -ecl.
- The left-hand-side quantity is the absorbance A.
- The linear relationship between absorbance, concentration, and path length is known as the Beer-Lambert law: A = ecl.
- Absorbance depends on path length (l) and concentration.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Quiz on photochemistry, a branch of chemistry involving chemical reactions triggered by light absorption. Explore electronic excitation and molecular activation.