ABSTRACT
Three basic approaches to predict the vapor pressure of chemicals within mixtures will be presented: Raoult’s law for ideal mixtures, how to calculate an empirical adjustment to Raoult’s law for nonideal mixtures, and Henry’s law for dilute mixtures in water. No model can predict all mixtures, but where models work, they can help industrial hygienists make much better decisions. Failure to anticipate that a mixture is not ideal can result in underestimating the health hazard and/or overexposing people to organic vapors from mixtures. Raoult’s law is based on the premise that the molecules within a liquid mixture all act independently of each other. The more different that the molecules of one chemical within a liquid mixture are from the other molecules around it, the more likely they are to interact and for its vapor pressure to deviate from Raoult’s law. This chapter describes such molecular interactions and various predictive models and empirical adjustments to Raoult’s law.
