Chem Thermo homework help

Alright, I'm trying to figure out why at this point in my code

phi=(phi_p_v)*(P_v/P)*exp((V_sat*(P-P_v))/(R*T))

it is only giving me a single number. Why wont P_v divide by the matrix P up to the number 22.27? I tried using P_v./P but it still doesn't work. Any help will be appreciated.

%Problem 11.24 part A

%Assuming that Eq (11.68) is valid for the vapor phase and that the molar
%volume of saturated liquid is given by eq (3.72), prepare plots of f vs P
%and of phi vs. P for Chloroform at 200 degrees Celcius for the pressure
%range from 0-40 bar. At 200 degrees Celcius, the vapor pressure of
%chloroform is 22.27 bar. 

clear
clc

%Given
P=[0:40]';
P_v=22.27; %bar
T=200+273.12; %K
R=8.314

P_c=54.72; %bar
T_c=536.4; %K
w=.222;
V_c=239; %cm^3/mol
Z_c=.265;

%Find T_r 
T_r=T/T_c
P_r=P/P_c

%Find V_sat
V_sat=(V_c)*(Z_c)^((1-T_r)^(2/7))

%Find B_0 and B_1
B_0=0.083-(.422/(T_r^1.6))
B_1=.139-(.172/(T_r^4.2))

%For P<=P_sat
phi_p_v=exp((P_v/P_c)/(T_r)*(B_0+w*B_1));

if P<=P_v
    phi=(phi_p_v)*(P_v/P)*exp((V_sat*(P-P_v))/(R*T))
else
    phi=exp((P_r)/(T_r)*(B_0+w*B_1))
end

%Graph them
plot (P,phi)
title ('phi vs. P')
xlabel ('Pressure, bar')
ylabel ('phi')

Answer 1

[Star Strider]

You need to test each value of ‘P’, then do the appropriate calculation:

for k1 = 1:length(P)
    Pn = P(k1);
    if Pn<=P_v
        phi(k1)=(phi_p_v)*(P_v./Pn).*exp((V_sat*(Pn-P_v))/(R*T));
    else
        phi(k1)=exp((P_r(k1))/(T_r)*(B_0+w*B_1));
    end
end

I created ‘Pn’ for each value of ‘P’ and changed the first ‘phi’ equation to accommodate it. That also required subscripting ‘P_r’ and subscripting ‘phi’ in both equations.

Does this do what you want?