A drug suspension decomposes by zero-order kinetics with a rate constant of 2 mg mL-1month-1. If the initial concentration is 100 mg mL-1, what is the shelf life (t10%)?

5 months

Explanation: Rate Law for a reaction is an equation relating the reaction rate of reactants. It is expressed as:

aA + bB → cC + dD

in which k is the rate constant of the reaction

Zero-order Kinetics is a chemical reaction in which the rate doesn't change with the variations in concentration of the reactants. At this state, it is possible to determine the final concentration by using:

Shelf-Life is the time required for 10% of a drug or material to desintegrate: it is the time necessary for A to desintegrate 90% of its original concentration.

Then, the shelf-life for the drug is

2t = 10

t = 5

Shelf-life for a drug which decomposes by zero-order kinetics with rate constant of 3mgmL^{-1}month^{-1} is 5 months

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current