Langmuir Isotherm
Environmental Engineering · FE Reference Handbook section
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
Langmuir isotherm monolayer adsorption model for carbon treatment Given maximum adsorption capacity (a) = 12.0000 mg/g; Langmuir equilibrium constant (b) = 0.0540 L/mg; equilibrium concentration (C_e) = 44.3000 mg/L, determine the adsorption capacity (x/m) (x_m) in mg/g.
Given
Find
adsorption capacity (x/m) (x_m), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 1 — schematic for Langmuir Isotherm — solve for adsorption capacity (x/m) — Langmuir Isotherm
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_m:
Step 3 — List the givens: maximum adsorption capacity (a) = 12.0000 mg/g, Langmuir equilibrium constant (b) = 0.0540 L/mg, equilibrium concentration (C_e) = 44.3000 mg/L.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_m = 8.4625 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 16.9249 — kept a factor of two that cancels in the correct rearrangement.
- 4.2312 — dropped that same factor in the other direction.
- 9.3087 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm linearized form used to determine adsorption constants Given maximum adsorption capacity (a) = 163.0 mg/g; Langmuir equilibrium constant (b) = 1.9480 L/mg; adsorption capacity (x/m) (x_m) = 132.2 mg/g, determine the equilibrium concentration (C_e) in mg/L.
Given
Find
equilibrium concentration (C_e), in mg/L
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 2 — schematic for Langmuir Isotherm — solve for equilibrium concentration — Langmuir Isotherm (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for C_e:
Step 3 — List the givens: maximum adsorption capacity (a) = 163.0 mg/g, Langmuir equilibrium constant (b) = 1.9480 L/mg, adsorption capacity (x/m) (x_m) = 132.2 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning C_e = 2.2034 mg/L to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.4068 — kept a factor of two that cancels in the correct rearrangement.
- 1.1017 — dropped that same factor in the other direction.
- 2.4237 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm adsorption capacity for water treatment design Given Langmuir equilibrium constant (b) = 1.2160 L/mg; equilibrium concentration (C_e) = 4.9000 mg/L; adsorption capacity (x/m) (x_m) = 169.5 mg/g, determine the maximum adsorption capacity (a) in mg/g.
Given
Find
maximum adsorption capacity (a), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except a is given, so isolate a symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 3 — schematic for Langmuir Isotherm — solve for maximum adsorption capacity — Langmuir Isotherm (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for a:
Step 3 — List the givens: Langmuir equilibrium constant (b) = 1.2160 L/mg, equilibrium concentration (C_e) = 4.9000 mg/L, adsorption capacity (x/m) (x_m) = 169.5 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning a = 197.9 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 395.9 — kept a factor of two that cancels in the correct rearrangement.
- 98.9736 — dropped that same factor in the other direction.
- 217.7 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm monolayer adsorption model for carbon treatment Given maximum adsorption capacity (a) = 104.0 mg/g; Langmuir equilibrium constant (b) = 1.7520 L/mg; equilibrium concentration (C_e) = 22.9000 mg/L, determine the adsorption capacity (x/m) (x_m) in mg/g.
Given
Find
adsorption capacity (x/m) (x_m), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 4 — schematic for Langmuir Isotherm — solve for adsorption capacity (x/m) (case 2) — Langmuir Isotherm (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_m:
Step 3 — List the givens: maximum adsorption capacity (a) = 104.0 mg/g, Langmuir equilibrium constant (b) = 1.7520 L/mg, equilibrium concentration (C_e) = 22.9000 mg/L.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_m = 101.5 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 202.9 — kept a factor of two that cancels in the correct rearrangement.
- 50.7354 — dropped that same factor in the other direction.
- 111.6 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm linearized form used to determine adsorption constants Given maximum adsorption capacity (a) = 159.0 mg/g; Langmuir equilibrium constant (b) = 0.5890 L/mg; adsorption capacity (x/m) (x_m) = 86.7000 mg/g, determine the equilibrium concentration (C_e) in mg/L.
Given
Find
equilibrium concentration (C_e), in mg/L
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 5 — schematic for Langmuir Isotherm — solve for equilibrium concentration (case 2) — Langmuir Isotherm (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for C_e:
Step 3 — List the givens: maximum adsorption capacity (a) = 159.0 mg/g, Langmuir equilibrium constant (b) = 0.5890 L/mg, adsorption capacity (x/m) (x_m) = 86.7000 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning C_e = 2.0359 mg/L to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.0719 — kept a factor of two that cancels in the correct rearrangement.
- 1.0180 — dropped that same factor in the other direction.
- 2.2395 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm adsorption capacity for water treatment design Given Langmuir equilibrium constant (b) = 1.9880 L/mg; equilibrium concentration (C_e) = 42.7000 mg/L; adsorption capacity (x/m) (x_m) = 65.0000 mg/g, determine the maximum adsorption capacity (a) in mg/g.
Given
Find
maximum adsorption capacity (a), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except a is given, so isolate a symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 6 — schematic for Langmuir Isotherm — solve for maximum adsorption capacity (case 2) — Langmuir Isotherm (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for a:
Step 3 — List the givens: Langmuir equilibrium constant (b) = 1.9880 L/mg, equilibrium concentration (C_e) = 42.7000 mg/L, adsorption capacity (x/m) (x_m) = 65.0000 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning a = 65.7657 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 131.5 — kept a factor of two that cancels in the correct rearrangement.
- 32.8829 — dropped that same factor in the other direction.
- 72.3423 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm monolayer adsorption model for carbon treatment Given maximum adsorption capacity (a) = 108.0 mg/g; Langmuir equilibrium constant (b) = 0.8500 L/mg; equilibrium concentration (C_e) = 2.1000 mg/L, determine the adsorption capacity (x/m) (x_m) in mg/g.
Given
Find
adsorption capacity (x/m) (x_m), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 7 — schematic for Langmuir Isotherm — solve for adsorption capacity (x/m) (case 3) — Langmuir Isotherm (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_m:
Step 3 — List the givens: maximum adsorption capacity (a) = 108.0 mg/g, Langmuir equilibrium constant (b) = 0.8500 L/mg, equilibrium concentration (C_e) = 2.1000 mg/L.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_m = 69.2208 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 138.4 — kept a factor of two that cancels in the correct rearrangement.
- 34.6104 — dropped that same factor in the other direction.
- 76.1429 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm linearized form used to determine adsorption constants Given maximum adsorption capacity (a) = 133.0 mg/g; Langmuir equilibrium constant (b) = 0.1920 L/mg; adsorption capacity (x/m) (x_m) = 102.7 mg/g, determine the equilibrium concentration (C_e) in mg/L.
Given
Find
equilibrium concentration (C_e), in mg/L
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 8 — schematic for Langmuir Isotherm — solve for equilibrium concentration (case 3) — Langmuir Isotherm (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for C_e:
Step 3 — List the givens: maximum adsorption capacity (a) = 133.0 mg/g, Langmuir equilibrium constant (b) = 0.1920 L/mg, adsorption capacity (x/m) (x_m) = 102.7 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning C_e = 17.6533 mg/L to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 35.3067 — kept a factor of two that cancels in the correct rearrangement.
- 8.8267 — dropped that same factor in the other direction.
- 19.4187 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm adsorption capacity for water treatment design Given Langmuir equilibrium constant (b) = 0.7660 L/mg; equilibrium concentration (C_e) = 11.4000 mg/L; adsorption capacity (x/m) (x_m) = 27.8000 mg/g, determine the maximum adsorption capacity (a) in mg/g.
Given
Find
maximum adsorption capacity (a), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except a is given, so isolate a symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 9 — schematic for Langmuir Isotherm — solve for maximum adsorption capacity (case 3) — Langmuir Isotherm (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for a:
Step 3 — List the givens: Langmuir equilibrium constant (b) = 0.7660 L/mg, equilibrium concentration (C_e) = 11.4000 mg/L, adsorption capacity (x/m) (x_m) = 27.8000 mg/g.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning a = 30.9835 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 61.9671 — kept a factor of two that cancels in the correct rearrangement.
- 15.4918 — dropped that same factor in the other direction.
- 34.0819 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm
Langmuir isotherm monolayer adsorption model for carbon treatment Given maximum adsorption capacity (a) = 100.0 mg/g; Langmuir equilibrium constant (b) = 1.7410 L/mg; equilibrium concentration (C_e) = 0.9000 mg/L, determine the adsorption capacity (x/m) (x_m) in mg/g.
Given
Find
adsorption capacity (x/m) (x_m), in mg/g
Start with the thinking
- The governing relation printed in this handbook section is Langmuir Isotherm.
- Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Langmuir isotherm describes monolayer adsorption capacity and can be expressed in a linearized form for parameter fitting.
Figure 10 — schematic for Langmuir Isotherm — solve for adsorption capacity (x/m) (case 4) — Langmuir Isotherm (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_m:
Step 3 — List the givens: maximum adsorption capacity (a) = 100.0 mg/g, Langmuir equilibrium constant (b) = 1.7410 L/mg, equilibrium concentration (C_e) = 0.9000 mg/L.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_m = 61.0425 mg/g to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 122.1 — kept a factor of two that cancels in the correct rearrangement.
- 30.5213 — dropped that same factor in the other direction.
- 67.1468 — rounded an intermediate value before the final step.
Reference: FE Handbook — Langmuir Isotherm