I am looking at the delta H chart to calculate delta H of reactions. When doing one reaction, I came across a species that was not included in the chart: SiO4. What do I do?
There is no SiO4. SiO2 perhaps, OR, you have been asked to calculate a theoretical molecule.
Oh, you are right, it is SiCl4, which is also not on my chart. So what should I do?
I have gaseous SiCl4 listed as -657.0 kJ/mol listed in one of my books for Delta Hfo
Oh, thanks! You must have a different book than I do. Thanks!
My number came from Whitten, Davis, Peck, 5th edition, General Chemistry, 1996. I also looked it up on the Internet using NIST tables. They show -662.
If you're unable to find the delta H value for a particular species, such as SiCl4, in your chart, there are a few options you can consider:
1. Use an alternative source: Consult different textbooks or online resources to gather information on the delta H value of SiCl4. As mentioned earlier, the value -657.0 kJ/mol for gaseous SiCl4 is listed in Whitten, Davis, Peck, 5th edition, General Chemistry, 1996. Additionally, the NIST tables also show a value of -662 kJ/mol for SiCl4.
2. Estimate the value: If you cannot find an exact delta H value for SiCl4, you may be able to estimate it based on the values available for similar compounds or reactions. Look for compounds or reactions with comparable chemical structures or thermodynamic properties and use their delta H values as a reference for estimation.
3. Consult with an expert: If you are conducting a specific experiment or dealing with a complex reaction, it's advisable to seek guidance from a chemistry professor or expert who may have access to more specialized resources or be able to provide insights based on their expertise.
Remember, delta H values are typically given in units of kJ/mol, representing the enthalpy change per mole of a substance involved in a reaction.
If you come across a species that is not included in the delta H chart you are using, there are a few options you can consider.
First, double-check to make sure you are correctly identifying the species. In your case, you mentioned SiO4, which does not exist as a stable compound. It is possible that you meant SiO2, which is silicon dioxide. In that case, you can look for the delta H value for SiO2 in your chart or reference materials.
If you still cannot find the value for a specific species, you can try to estimate it using other known values. For example, if you have data for related compounds that are similar to the one you are interested in, you can use those values to estimate the delta H. This can be done by considering the stoichiometry and the relative energy differences between compounds.
Additionally, you can check other reference materials such as different textbooks, scientific literature, or online databases like NIST (National Institute of Standards and Technology). These sources often provide comprehensive and reliable data, including delta H values for various compounds, including SiCl4 in your case.
It is important to note that different sources may have slightly different values due to variations in experimental methods or different sets of data used for calculations. Therefore, it is advisable to cross-reference multiple sources to get a better understanding and ensure accuracy.
Using these methods, you can obtain an estimated or accurate value for the delta H of the species you are interested in, even if it is not explicitly listed in your initial chart.