Calculate Boiling Point At Different Pressures

Boiling Point Equation:

\[ T_b = \frac{1}{\frac{1}{T_0} - \frac{R}{\Delta H_{vap}} \ln \left( \frac{P}{P_0} \right)} \]

Reference Boiling Point (T₀):

Enthalpy of Vaporization (ΔH_vap):

J/mol

Pressure (P):

Reference Pressure (P₀):

Boiling Point (T_b):

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1. What is the Boiling Point Equation?

The boiling point equation calculates the boiling temperature of a substance at different pressures using the Clausius-Clapeyron relation. It accounts for how pressure changes affect the boiling point of liquids.

2. How Does the Calculator Work?

The calculator uses the boiling point equation:

\[ T_b = \frac{1}{\frac{1}{T_0} - \frac{R}{\Delta H_{vap}} \ln \left( \frac{P}{P_0} \right)} \]

Where:

\( T_b \) — Boiling point at pressure P (K)
\( T_0 \) — Reference boiling point at pressure P₀ (K)
\( R \) — Gas constant (8.314 J/mol·K)
\( \Delta H_{vap} \) — Enthalpy of vaporization (J/mol)
\( P \) — Pressure (Pa)
\( P_0 \) — Reference pressure (Pa)

Explanation: The equation shows the inverse relationship between pressure and boiling point - as pressure decreases, boiling point decreases, and vice versa.

3. Importance of Boiling Point Calculation

Details: Accurate boiling point calculation is crucial for chemical processes, distillation, food processing, and understanding how altitude affects cooking temperatures.

4. Using the Calculator

Tips: Enter all values in the specified units. Reference values (T₀ and P₀) are typically measured at standard atmospheric pressure (101325 Pa). All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: Why does boiling point change with pressure?
A: Pressure affects the energy required for liquid molecules to escape into the vapor phase. Lower pressure means less energy needed, thus lower boiling point.

Q2: What are typical ΔH_vap values?
A: Water has ΔH_vap ≈ 40.65 kJ/mol. Organic solvents typically range from 20-50 kJ/mol depending on molecular weight and intermolecular forces.

Q3: How does altitude affect boiling point?
A: At higher altitudes, atmospheric pressure is lower, causing water to boil at lower temperatures (≈90-95°C at 3000m instead of 100°C).

Q4: Are there limitations to this equation?
A: The equation assumes constant ΔH_vap and ideal gas behavior. It works best for moderate pressure changes and may be less accurate for extreme conditions.

Q5: Can this be used for all substances?
A: The equation applies to most pure liquids, but accuracy may vary for mixtures or substances with complex molecular interactions.