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## Using Henry's Law and Solve Blocks in Chemistry and Environmental Engineering  1-Newbie

## Using Henry's Law and Solve Blocks in Chemistry and Environmental Engineering

By D.M. Griffin, Jr. This worksheet will:

• Solve 6 equations 100 times and then plot each species as a function of the overlying partial pressure of H₂S, and determine how the H₂S partitions between the liquid and gas phases
• Apply in Chemistry and Environmental Engineering
• Performs Henry's law, solve blocks, graphs, fraction and partial pressure equations, etc.

This worksheet using Mathcad sets up a problem where a 500 ftᶾ pump station well contains 500 gallons of anoxic wastewater. The bacteria in this wastewater produce H₂S which both produces a bad smell and can be dangerous for workers. This worksheet helps you to find what fraction of the total moles of sulfide would exist as H₂S and how much of it would escape into the overlying wet well atmosphere. To begin, this worksheet provides an equation according to Henry's Law, which describes the partitioning of H₂S between the liquid and the overlying gas phase. This produces 6 unknowns, which requires 6 equations for solving.

The worksheet then provides you with some initial guesses and also sets up constraints so that all concentrations must be greater than zero. Next, the worksheet defines a function, which is actually a solve block, to find the equations for each value of the partial pressure of H₂S. This is then graphed to show the Sulfide species distribution as a function of partial pressure. Next you are shown how to compute the fraction of the total sulfide that exists in the gas phase as a function of the partial pressure of H₂S and how to compute the fraction of total sulfide that is in the gas phase at this pH. This is then graphed.

This worksheet helps you to solve a set of 6 simultaneous equations 100 times and then plots each species as a function of the overlying partial pressure of H₂S. Henry's Law also is used to determine how the H₂S partitions itself between the aqueous and gaseous phases.

All notation, formulas, calculations, solutions, graphs, and summaries have been provided to help you in your own calculations. 