Sunscreen
Name two chemical ingredients in sunscreen that were mentioned in our presentation
Zinc oxide, titanium dioxide, octisalate, avobenzone
Does the sun cook you or do you cook yourself when it comes to sunburns?
You cook yourself!!! - This is because your body absorbs these rays and converts into heat triggering inflammation and the burning of melanin
What type of frequency and wavelength does UV rays have?
High frequency and short wavelengths!
How does Beer-Lambert's Law relate to sunscreen?
Absorbance & emittance
Is the degradation of sunscreen exothermic or endothermic driven?
Endothermic reaction
What is the difference between mineral and chemical sunscreen?
- Mineral sunscreen absorbs UV rays from the skin surface while chemical sunscreen absorbs UV rays within the skin
- Chemical sunscreen degrades way faster than mineral sunscreen
Do more people in the world tan or burn?
Tan!!!
In the photoelectric effect, do the amount of joules need to be greater, less than or equal to the energy threshold for the effect to be working.
Greater than!
As absorbance increases, what happens to the concentration and thickness of the sunscreen?
Increases -> direct relationship
Math time!
If 420 J of energy is absorbed by 35.0 g of sunscreen and the temperature increases from 22.0°C to 28.0°C, what is the specific heat capacity of the sunscreen?
2.0 J g^-1 * C^-1
Delta T = 28.0 - 22.0 = 6.0 degrees C
q= mcat --> c = q/mat --> 420/(35.0)(6.0)c= 420/210
What are the two types of UV that sunscreen blocks?
UVA & UVB
What is the name of the malignant cancer you can get from the sun?
Melanoma
Explain how the photoelectric effect relates to sunburns (verbal explanation)
UV light carries high-energy photons. Photons hit a material and transfer energy to electrons. When UV photons hit your skin, they transfer enough energy to molecules and electrons in skin cells to damage DNA and tissues, leading to inflammation and sunburn.
Describe all of the variables in Beer-Lambert's Law and how it relates to sunscreen.
A = εlc
A = absorbance, how much UV light is absorbed
ε = molar absorptivity, how strong is it absorbed
l = path length, distance UV light travels
c = concentration, amt of UV-absorbing present
A sunscreen manufacturer is developing a new lotion that spreads spontaneously across the skin when exposed to sunlight. The chemists determine that the spreading process has the following info:
Delta H = -85 kj/mol & Delta S = -120 J/mol
At what temperatures is this process thermodynamically favorable?
Favorable only at low temperatures; explanation is that both delta H and delta S is negative so in
Delta G = Delta H - TAS --> - TAS is positive @ higher temps... so that is thermo unfavorable need opposite