OZ1 + OZ2: Light and Energy
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How do you convert from ppm to %?
Divide by 10,000
How do you convert from % to pmm?
Multiply by 10,000
In which two ways is light described as?
• A wave - A particle
What is the equation for working out the speed of light?
Speed of light (c) = wavelength (λ) x frequency (v)
What is the speed of light?
3.00 x 10^8 ms^-1
What is the unit for wavelength?
m (metres)
What is the unit for frequency when working out the speed of light?
s^-1
What is the equation for working out energy using plank’s constant?
Energy (E) = Plank’s constant (h) x frequency (v)
What is the unit for energy?
J (Joules)
What is Plank’s Constant?
6.63 x 10^-34 JHz^-1
What is the unit for frequency when working out energy?
Hz (hertz)
What is the equation for working out energy with both speed of light and Plank’s Constant?
E = h x c/ λ
What does energy’s interaction with chemicals depend on? (2)
• The type of chemical - The amount of energy involved
What 4 types of behaviour do molecules have in order of which requires the most energy to which requires the least?
• Electronic energy • Vibrational energy • Rotational energy • Translational energy
Why do changes in rotational energy require a lower frequency of light on the EM spectrum to be absorbed than changes in vibrational energy?
Making molecules rotate requires less energy than making bonds within a molecule stretch
What energy and type of light on the EM spectrum does changing the electronic energy level correspond to?
• 1x10^-19 to 1x10^-16 J - UV and visible
What energy and type of light on the EM spectrum does changing the vibrational energy level correspond to?
• 1x10^-20 to 1x10^-19 J - Infrared
What energy and type of light on the EM spectrum does changing the rotational energy level correspond to?
• 1x10^-22 to 1x10^-20 J - Microwave
Why are the amounts of energy required for different energy changes given in ranges?
The size of the energy change depends on the strength of the substance’s bond
What three types of electronic changes occur when molecules absorb UV light (in order of increasing energy absorbed)?
• Electrons are excited to a higher energy level • Photodissociation • Ionisation
How are electrons excited to a higher energy level?
They absorb the UV energy and jump up
What is photodissociation?
• So much energy is absorbed that bonding electrons cannot keep atoms together. • Radicals are formed.
What is ionisation?
When an electron leaves a molecule turning it into an ion