After 20 min, a reactant has decomposed to 85 % of its original concentration. Which order would the reaction need to be to allow you to solve for the rate constant, k , with only this information?

Answer : The value of rate constant is,

Explanation :

First we have to calculate the rate constant, we use the formula :

Expression for rate law for first order kinetics is given by:

where,

k = rate constant  = ?

t = time passed by the sample  = 20 min

a = let initial amount of the reactant  = 100 g

a - x = amount left after decay process = 100 - 85 = 15 g

Now put all the given values in above equation, we get

Therefore, the value of rate constant is,

a

explanation:

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2