Vapour pressure

What is vapour pressure?

Vapour pressure is the pressure exerted by a substance’s vapour when it is in equilibrium with its liquid or solid phase at a specific temperature. It increases with temperature and is a fundamental physical property used to predict how readily a chemical will evaporate. Substances with high vapour pressures at room temperature are considered volatile and may pose inhalation hazards or contribute to air pollution.

Why is vapour pressure important in chemical safety and regulation?

In regulatory frameworks such as REACH, GHS, and TSCA, vapour pressure data is essential for classifying chemicals by hazard. It informs risk assessments related to flammability, toxicity via inhalation, and environmental persistence. For example, a high vapour pressure may necessitate controlled storage conditions or personal protective equipment (PPE) in laboratory and industrial settings. In procurement, understanding vapour pressure helps select materials suitable for specific environments, such as low-volatility solvents for sensitive processes.

How is vapour pressure measured and reported?

Vapour pressure is typically measured using methods such as the static method, isoteniscope, or gas chromatography. Results are reported in units such as pascals (Pa), kilopascals (kPa), or millimetres of mercury (mmHg). Standard reference data are available in databases like the NIST Chemistry WebBook or CAS registry. For regulatory compliance, vapour pressure values must be reported in accordance with ISO or OECD guidelines, and included in Safety Data Sheets (SDS) and Certificates of Analysis (CoA).

Related concepts

Vapour pressure is closely linked to boiling point, volatility, and Henry’s law. It is also used in conjunction with other physical properties such as flash point and solubility to assess chemical risk and environmental fate.