I wrote a piece of code about Calculating the Enthalpy of H2, O2, and Water and the machine reports the error "Array indices must be positive integers or logical values".

R = 8.314; % Ideal Gas Constant

T = 300 : 50 : 1000; % Temperature range from 300 K to 1000 K with increments of 50

% Create Temperature Loop

I = 0; % Initialization of loop variable

for T = 300 : 50 : 1000; % Temperature range from 300 K to 1200 K with increments of 50

I = I + 1; % Loop variable

% Hydrogen enthalpy calculations

hf_h = 0; % Hydrogen enthalpy at the standard state

hs_h = R*(((3.057 * T) + ((1/2) * 2.677E-3 * T^2) - ((1/3) * 5.810E-6 * T^3) + ((1/4) * 5.521E-9 * T^4) - ((1/5) * 1.812E-12 * T^5)) - (3.057 * 298 + ((1/2) * 2.677E-3 * 298^2) - ((1/3) * 5.810E-6 * 298^3) + ((1/4) * 5.521E-9 * 298^4) - ((1/5) * 1.812E-12 * 298^5)));

H_hydrogen = (hf_h + hs_h); % Enthalpy of Hydrogen

hf_o = 0; % Oxygen enthalpy at the standard state

hs_o = R * (((3.626 * T) - ((1/2) * 1.878E-3 * T^2) + ((1/3) * 7.055E-6 * T^3) - ((1/4) * 6.764E-9 * T^4) + ((1/5) * 2.156E-12 * T^5)) - (3.626 * 298 - ((1/2) * 1.878E-3 * 298^2) + ((1/3) * 7.055E-6 * 298^3) - ((1/4) * 6.764E-9 * 298^4) + ((1/5) * 2.156E-12 * 298^5)));

H_oxygen = (hf_o + hs_o); % Enthalpy of Oxygen

% Water enthalpy calculations

hf_w = -241820; % Water enthalpy at the standard state

hs_w = R * (((4.070 * T) - ((1/2) * 1.108E-3 * T^2) + ((1/3) * 4.152E-6 * T^3) - ((1/4) * 2.964E-9 * T^4) + ((1/5) * 0.807E-12 * T^5)) - (4.070 * 298) - ((1/2) * 1.108E-3 * 298^2) + ((1/3) * 4.152E-6 * 298^3) - ((1/4) * 2.964E-9 * 298^4) + ((1/5) * 0.807E-12 * 298^5));

H_water = (hf_w + hs_w) % Enthalpy of Water

% Create new variables to save the new calculated values for hydrogen, oxygen, and water enthalpy at each temperature increment

Hydrogen_Enthalpy(i) = H_hydrogen;

Oxygen_Enthalpy(i) = H_oxygen;

Water_Enthalpy(i) = H_water;

Temperature(i) = T;

end % End Loop

[Dyuman Joshi]

You could vectorize the loop.

Answer 1

[VBBV]

R = 8.314; % Ideal Gas Constant
T = 300 : 50 : 1000; % Temperature range from 300 K to 1000 K with increments of 50
% Create Temperature Loop
I = 0; % Initialization of loop variable
for T = 300 : 50 : 1000; % Temperature range from 300 K to 1200 K with increments of 50
I = I + 1; % Loop variable
% Hydrogen enthalpy calculations
hf_h = 0; % Hydrogen enthalpy at the standard state
hs_h = R*(((3.057 * T) + ((1/2) * 2.677E-3 * T^2) - ((1/3) * 5.810E-6 * T^3) + ((1/4) * 5.521E-9 * T^4) - ((1/5) * 1.812E-12 * T^5)) - (3.057 * 298 + ((1/2) * 2.677E-3 * 298^2) - ((1/3) * 5.810E-6 * 298^3) + ((1/4) * 5.521E-9 * 298^4) - ((1/5) * 1.812E-12 * 298^5)));
H_hydrogen = (hf_h + hs_h); % Enthalpy of Hydrogen
hf_o = 0; % Oxygen enthalpy at the standard state
hs_o = R * (((3.626 * T) - ((1/2) * 1.878E-3 * T^2) + ((1/3) * 7.055E-6 * T^3) - ((1/4) * 6.764E-9 * T^4) + ((1/5) * 2.156E-12 * T^5)) - (3.626 * 298 - ((1/2) * 1.878E-3 * 298^2) + ((1/3) * 7.055E-6 * 298^3) - ((1/4) * 6.764E-9 * 298^4) + ((1/5) * 2.156E-12 * 298^5)));
H_oxygen = (hf_o + hs_o); % Enthalpy of Oxygen
% Water enthalpy calculations
hf_w = -241820; % Water enthalpy at the standard state
hs_w = R * (((4.070 * T) - ((1/2) * 1.108E-3 * T^2) + ((1/3) * 4.152E-6 * T^3) - ((1/4) * 2.964E-9 * T^4) + ((1/5) * 0.807E-12 * T^5)) - (4.070 * 298) - ((1/2) * 1.108E-3 * 298^2) + ((1/3) * 4.152E-6 * 298^3) - ((1/4) * 2.964E-9 * 298^4) + ((1/5) * 0.807E-12 * 298^5));
H_water = (hf_w + hs_w) % Enthalpy of Water
% Create new variables to save the new calculated values for hydrogen, oxygen, and water enthalpy at each temperature increment
Hydrogen_Enthalpy(I) = H_hydrogen;
Oxygen_Enthalpy(I) = H_oxygen;
Water_Enthalpy(I) = H_water;
Temperature(I) = T;
end % End Loop

H_water = -2.4205e+05

H_water = -2.4037e+05

H_water = -2.3866e+05

H_water = -2.3694e+05

H_water = -2.3519e+05

H_water = -2.3342e+05

H_water = -2.3162e+05

H_water = -2.2979e+05

H_water = -2.2793e+05

H_water = -2.2604e+05

H_water = -2.2412e+05

H_water = -2.2217e+05

H_water = -2.2019e+05

H_water = -2.1818e+05

H_water = -2.1613e+05

[VBBV]

use the loop counter index I , the variable i , j are reserved to represent complex numbers in Matlab