Two chemicals A and B are combined to form a chemical C. The rate, or velocity, of the reaction is proportional to the product of the instantaneous amounts of A and B not converted to chemical C. Initially, there are 40 grams of A and 50 grams of B, and for each gram of B, 2 grams of A is used. It is observed that 25 grams of C is formed in 8 minutes. How much (in grams) is formed in 16 minutes

Respuesta :

Answer: 45. 78 g  is formed in 16 minutes.

Explanation:

Let [tex]A_{o} =40 g[/tex] and [tex]B_{o} =50 g[/tex]

we know that [tex]\alpha =A_{o}\frac{M+N}{M}\, and \, \beta =B_{o}\frac{M+N}{N}[/tex]

According to the question to create [tex]x[/tex] part of the chemical C we will need 2 part of A and one part of B.

Therefore, M = 2 and N = 1.

Now, we can easily solve  for the value of α and β.

[tex]\alpha =40\frac{2+1}{2}=60\\\\\, and \, \beta =50\frac{2+1}{1}=150[/tex]

Now, the differential equation must be: [tex]\frac{dX}{dt}=k\left ( \alpha -X \right )\left ( \beta -X \right )[/tex]

I separate the variable and solve the equation

[tex]\int \frac{dx}{\left ( 60-x \right )\left ( 150-x \right )}=\int k\, dt[/tex]

[tex]ln\frac{150-x}{60-x}=90kt+C_{1}[/tex]

By using [tex]X(0) =0[/tex],

[tex]\frac{150-x}{60-x}=Ce^{90k_{o}},C=\frac{5}{2}[/tex]

and using [tex]X (8)=25[/tex] and solving for the value of 'k'

[tex]\Rightarrow \frac{150-25}{60-25}=\frac{5}{2}e^{450k}\\\\\Rightarrow 3.6\times \frac{2}{5}=e^{450k}\\\\\Rightarrow 1.4=e^{450k}[/tex]

Taking 'ln' both side, we get

[tex]\Rightarrow k=7.4716\times 10^{-4}[/tex]

We obtain:[tex]X(t)=\frac{60Ce^{90kt}-150}{Ce^{90kt}-1}[/tex]

Now, for the 16 min

[tex]\Rightarrow X(16)=\frac{150e^{1.07559}-150}{2.5e^{1.0759}-1}[/tex]

[tex]\Rightarrow X(16)=\frac{439.7583-150}{7.3293-1}\\\\\Rightarrow X(16)=\frac{289.7583}{6.3293}[/tex]

[tex]\Rightarrow X(16)=45.78 g[/tex]