Selecting a chemical:
Chemicals are selected by one of two methods:
- Entering the Chemical Abstract Service (CAS) number. The CAS number is a unique identifier for each chemical. CAS numbers can be up to 10 digits, separated by two hyphens, where the last digit is a checksum. For example, water is given the CAS number 7732-18-5.
- Entering a few characters, describing the beginning of chemical name, will create a pull-down list of chemicals. For example, entering “tu” will create a list of tungsten compounds. This list is limited to the first 50 matches. Be aware that many chemicals have multiple names. For instance, water can also be correctly called “dihydrogen oxide”. Note that the chemical name search is based on “common” names (not IUPAC) and may not return “expected” names. For convenience, a link to the NIST website can be used when a CAS number search is needed.
Temperature axis:
The temperature or x-axis mat be expressed in units of Celsius (oC), Kelvin (oK) or Fahrenheit (oF). Kelvin is the Système International (SI) unit of temperature.
Pressure axis:
The pressure or y-axis may be expressed in units of mmHg, Pascal, kPascal, Bar, or Atmosphere (Atm). Pascal is the SI unit of pressure. In addition, the pressure axis may be plotted on a linear or log10 scale.
Interactive plot:
A “rule mark” can be dragged (using your finger on iPad or mouse on macOS) across the graph and will update the temperature/pressure display at the top of the graph.
Vapor Pressure calculator:
Specific values for temperature or pressure may be entered under the vapor pressure calculator. If a temperature is entered, the calculator will return a pressure corresponding to that entered temperature. If a pressure is entered, the calculator will return a temperature corresponding to that entered pressure. In some cases, the calculator may be more precise than the graph, since the graph has a fixed number of points.
Limitations:
All of the vapor pressure calculations are based on the semi-emperical Antoine equation, which has its limitations. Specifically, the equation is only valid over a well defined temperature range. This range appears under the Chemical Properties box. If a value outside of this range is entered into the Vapor Pressure calculator, the App will automatically set the temperature to either the low or high range limit.
© Steven W. Sharpe