[geterdun]

Hello, I haven't found any posts directly addressing this topic, so here goes:

I have an assignment requiring F-E modeling of steady-state approximations v. exact set. I am using Excel to numerically integrate, my h=1.0 for t=0-100, and I am comfortable with the numerical process. However, I am not as confident in my system of equations.

The given rxn equation is: 2A(g) + B(g) C(g) 3D(g)

My present system is as follows:

d[A]/dt = 2k₁'[C] - 2k₁[A]²B
dB/dt = k₁'[C] - k₁[A]²B
d[C]/dt = k₁[A]²B - (k₁' + k₂)[C] + k₂'[D]³
d[D]/dt = 3k₂[C] - 3k₂'[D]³

*apparently, if I put B in [] it bolds everything? Any way around this?

My steady-state requires that d[C]/dt = 0, so this yields a solvable equation for [C] which I then plug into my approximate set along with the provided rate constants and initial conditions and let Excel do the magic.

Can anyone confirm (or refute!) that my system of differentials is indeed correct for this problem?

I feel like I'm 95% of the way there, but those darn coefficients are eluding me at the moment. I know that -1/3dD/dt = dC/dt = -1/2dA/dt = -dB/dt. Have I applied this knowledge correctly? 

Thanks!

[esf.edu]

Your last equation has an error: the extra 3 in front of the first term.  It should be
d[D]/dt = k₂[C] - 3k₂'[D]³

 This assumes, of course, that these are elementary reactions, so the rate law can be written from the balanced chemical reaction.  My favorite counterexample is methane combustion, which is not an elementary reaciton:
   CH₄ + 2O₂  CO₂ + 2H₂O

[geterdun]

These are elementary reactions, so assumption holds.

However, can you please explain your logic for the omission of the 3 coefficient? To me, this suggests that I should also remove the coefficient from the 2k1'[C] in d[A]/dt. And since (1/2)dA/dt = dB/dt, I'd have to change dB/dt as well.

[juanrga]

Hello, I haven't found any posts directly addressing this topic, so here goes:

I have an assignment requiring F-E modeling of steady-state approximations v. exact set. I am using Excel to numerically integrate, my h=1.0 for t=0-100, and I am comfortable with the numerical process. However, I am not as confident in my system of equations.

The given rxn equation is: 2A(g) + B(g) C(g) 3D(g)

My present system is as follows:

d[A]/dt = 2k₁'[C] - 2k₁[A]²B
dB/dt = k₁'[C] - k₁[A]²B
d[C]/dt = k₁[A]²B - (k₁' + k₂)[C] + k₂'[D]³
d[D]/dt = 3k₂[C] - 3k₂'[D]³

*apparently, if I put B in [] it bolds everything? Any way around this?

My steady-state requires that d[C]/dt = 0, so this yields a solvable equation for [C] which I then plug into my approximate set along with the provided rate constants and initial conditions and let Excel do the magic.

Can anyone confirm (or refute!) that my system of differentials is indeed correct for this problem?

I feel like I'm 95% of the way there, but those darn coefficients are eluding me at the moment. I know that -1/3dD/dt = dC/dt = -1/2dA/dt = -dB/dt. Have I applied this knowledge correctly? 

Thanks!

It is correct.

Regarding bold face problem, use [ B] or [B ] or some other trick for concentration of B.

[geterdun]

Thanks juanrga. I've ironed out my model, got great results.