The light-stimulated conversion of 11-cis-retinal to 11-trans-retinal is central to the vision process in humans. This reaction also occurs (more slowly) in the absence of light. At 80.0 ∘C in heptane solution, the reaction is first order with a rate constant of 1.02×10−5/s. How many hours does it take for the concentration of 11-trans-retinal to reach 3.14×10−3 M ? (Note: 11-cis-retinal + 11-trans-retinal = total amount of retinal in eye)

See explanation

Explanation:

For first order reaction;

ln[A] = ln [A]o - kt

Where;

[A] = concentration at time = t

[A]o = initial concentration

k = rate constant

t = time taken

i) ln[A] = ln( 3.2×10−3 M) - (1.02×10−5/s * 6 * 60 * 60)

ln[A] =  -5.745 - 0.22

[A] = e^-5.965

[A] = 2.6 * 10^-3

ii) Now, Amount reacted = 0.25 * 3.2×10−3 M = 8 * 10^-4 M

[A] = 3.2×10−3 M - 8 * 10^-4 M

[A] = 2.4 ×10−3 M

ln[A] = ln [A]o - kt

ln[A]  - ln [A]o = - kt

t = ln[A]  - ln [A]o/-k

t = ln(2.4 ×10−3 M) -ln (3.2×10−3 M)/-(1.02×10−5/s)

t= -6.032 - (-5.745)/-(1.02×10−5/s)

t = -0.287/-(1.02×10−5/s)

t = 468.95 minutes

iii) t = ln[A]  - ln [A]o/-k

t = ln(3.15×10−3 M) - ln (3.2×10−3 M)/-(1.02×10−5/s)

t = -5.760 - (-5.745)/-(1.02×10−5/s)

t = -0.015/-(1.02×10−5/s)

t = 0.41 hours

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.