I am using the element names as symbolic variables to make the answer look nice. Why will it not perform the function when my equivalence ratio is more than one?

if phi > 1
    N_rO2 = a/phi;
    N_rN2 = a*3.76/phi;
    N_CO2 = x/phi;
    N_H2O = y/(2*phi);
    N_pO2 = 0;
    N_pN2 = N_rN2;
    N_pfuel = (1 - (1/phi))*fuel;
end

fuel + N_rO2*O2 + N_rN2*N2 
disp('<=>')
(N_CO2*CO2)+(N_H2O*H2O)+(N_pO2*O2)+(N_pN2*N2)+(N_pfuel*fuel)

Error using  * 
Inner matrix dimensions must agree.

Error in ReactantMolFractions (line 59)
(N_CO2*CO2)+(N_H2O*H2O)+(N_pO2*O2)+(N_pN2*N2)+(N_pfuel*fuel)

[Stephen23]

@Elizabeth Browne: I suspect that you need to learn about the differences between matrix operations and array operations:

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

If any of phi, a, x, y, etc. are non-scalar, then probably none of your * and / operations are actually doing what you think they are doing. But because your code contains no comments or explanation, this is just a guess.

[Elizabeth Browne]

I am sure I need to learn more. I am a newbie, but I figured out which variable was not a scalar.

I appreciate the quick response though! I struggled with this for quite awhile before asking for help. Funny that as soon as I asked I figured it out.

Thank you!