Home Podcasts THMG132 – Vapor Pressure vs. Volatility

THMG132 – Vapor Pressure vs. Volatility

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Volatility Ahead Road Warning Sign , 3d render

In this episode, Bob and Mike explore the differences between vapor pressure and volatility.

Thank to our sponsor, CBRNE Convergence World 2018. This show will be held in Orlando, Florida, USA. Click here for registration information and other fantastic information.

Complete Show Notes

5:15 What are Vapor Pressure and Volatility?

  • Vapor pressure:
    • Physical property that can be measured – no chemical change
    • Simply put, it’s the ability of a substance to drive vapor into the air
    • Directly correlates with temperature
  • Volatility:
    • Simply put, it’s the tendency of a substance to vaporize
    • Expresses comparisons in terms of – i.e. [Chemical A] is more/less volatile than [Chemical B]
    • Provides context and perspective

12:45 Measuring Vapor Pressure

  • Can be measured in two ways:
  • We need a standard temperature reference to take an accurate measurement
  • When the vapor pressure and atmospheric pressure is equal, we have boiling
  • When the pressure of vaporization meets the atmospheric pressure, we reach equilibrium
  • We can’t reach equilibrium if the vessel is open – this relates to volatility
    • This is when the rate of evaporation is equal to the rate of condensation
    • Both of these are phase changes and are happening simultaneously

22:45 Vaporization vs. Volatilization

  • In general, heavyweight compounds produce small amounts of vapor
  • Conversely, lightweight compounds produce significant amounts of vapor
  • In closed vessels, pressure might build (volatility) – the higher the pressure inside the closed vessel, the higher the vapor pressure
  • Liquids with low boiling points have high vapor pressures, and liquids with high boiling points have low vapor pressures
  • Bob and Mike recommending having the vapor pressure of a few chemicals memorized (i.e. water or acetone) for reference points

26:15 How Vapor Pressure Impacts Our Decisions and Safety

  • Production of vapors is a major indicator of responder safety
  • Vapor is the physical form of a substance that’s most dangerous for us – inhalation and flammability
  • Vapor pressure affects transportation decisions for responders
  • This is because we may not be able to overpack a liquid with a high vapor pressure if there’s a possibility of the vessel’s pressure becoming too high

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2 COMMENTS

  1. Great podcast, very enlightening! Aside from the relationship between Vapor Pressure and Volitility, what about the relationship between Volitiliity and the distance between a products LEL and UEL?

    • Great point Mark!

      I am trying to find ways to tease out the subtly and nuance of deeper understanding of the Chemical and Physical properties of Hazmat. This is one of them.

      Thanks!

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