Van't Hoff Equation Calculator

Compute equilibrium constant (K) dependence on temperature (T) using ΔH° and ΔS° or lnK vs 1/T plots. For students, researchers, and lab technicians. Supports scientific notation (1e-3) and multiple units (kJ, kcal, °C, K). Runs entirely offline.

Educational only. Follow your lab SOPs and SDS.

Calculator

Method

ΔH° (standard enthalpy)

Enter negative for exothermic, positive for endothermic.

ΔS° (standard entropy)

Temperature

Precision

Results

Results will appear here.

Intermediate Values

Quality Checks

Understanding the Van't Hoff Equation

The Van't Hoff equation quantitatively describes how the equilibrium constant (K) changes with temperature for a given reaction. This is crucial for designing industrial reactors, optimizing synthesis conditions, and understanding biological systems.

Step-by-Step Usage

Choose method: Select from ΔH° & ΔS°, two-temperature data, or prediction.
Input values: Enter numbers with proper units. Use scientific notation (e.g., 2.5e-4).
Review results: Check main result, intermediate steps, and warnings.
Export if needed: Copy or export for your lab notebook.

Realistic Examples

Example 1: From ΔH° & ΔS°

ΔH° = -45.0 kJ/mol, ΔS° = -120 J/(mol·K) at 25°C → K ≈ 1.24 × 10⁻⁶ (exothermic, entropy-unfavorable).

Example 2: Two-point determination

K₁ = 0.01 at 300 K, K₂ = 0.04 at 350 K → ΔH° ≈ 47.8 kJ/mol (endothermic).

Example 3: Predicting K

K = 0.1 at 298 K, ΔH° = 25 kJ/mol → at 310 K, K ≈ 0.14 (increased with temperature for endothermic reaction).

Reference Table: Common Constants & Conversions

Constant	Value	Notes
Gas constant (R)	8.314462618 J/(mol·K)	Used in ΔG° = -RT lnK
1 cal	4.184 J	Thermochemistry conversion
0°C	273.15 K	Temperature conversion

Common Mistakes Checklist

Using ΔH in kJ/mol but R in J/(mol·K) without unit conversion.
Forgetting that T must be in Kelvin for all equations.
Assuming ΔH° is constant over large temperature ranges (>100 K).
Misinterpreting K < 1 as "no reaction" (it indicates reactant-favored).

Quick ΔH° Unit Converter

Convert between common enthalpy units instantly.

J/mol

kJ/mol

kcal/mol

Values update as you type. 1 cal = 4.184 J.

Frequently Asked Questions

What are the accuracy limits of this tool?

It assumes ideal behavior and constant ΔH° over the temperature range. For phase changes or large ΔCp, consider more advanced models.

When do the approximations fail?

When ΔH° varies significantly with T (non‑linear lnK vs 1/T plot), or for reactions involving gases at high pressure (non‑ideal).

What are common unit pitfalls?

Mixing J and kJ, forgetting Celsius‑to‑Kelvin conversion, and using cal without converting to J (R is in J).

Any measurement tips for K determination?

Use multiple temperature points, ensure equilibrium is reached, and consider using spectroscopic or conductivity methods for accuracy.

Safety notes for temperature‑dependent studies?

Use appropriate heating/cooling equipment, monitor for thermal runaway in exothermic reactions, and always consult SDS for thermal stability.

Formulas & Assumptions

Integrated Van't Hoff equation: ln(K₂/K₁) = ‑(ΔH°/R) (1/T₂ ‑ 1/T₁)
From ΔG° = ΔH° ‑ TΔS° and ΔG° = ‑RT lnK: lnK = ‑ΔH°/(RT) + ΔS°/R
Assumptions: ΔH° and ΔS° are constant over T range; ideal behavior; single equilibrium.
Constants: R = 8.314462618 J/(mol·K); 1 cal = 4.184 J.
Rounding: Results rounded to selected decimal places; intermediate calculations use double precision.

Disclaimer: For informational and educational purposes only. Estimates depend on your inputs and simplifying assumptions. This tool does not replace professional judgment, lab SOPs, or safety procedures. Always follow SDS guidance and institutional policies.

Sources & References:

Common chemistry constants: R, NA, F; Standard unit conversions and lab measurement best practices; General analytical chemistry and uncertainty concepts; Intro physical chemistry relationships (ideal gas, Arrhenius, equilibrium); Laboratory safety basics and SDS principles.

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Van't Hoff Equation Calculator

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