Stoichiometry and chemical equations

In the reaction in Example 4-1, triethylene glycol is a liquid, oxygen and carbon dioxide are gases, and water is a liquid. Such facts as these are inconsequential if our interest is only in balancing an equation. Still, we convey a more complete representation of the reaction by including this information, and sometimes it is essential to include such information in a chemical equation. The state of matter or physical form of reactants and products is shown by symbols in parentheses. 

the equation for combustion of triethylene glycol can be written as 

Another commonly used symbol for reactants or products dissolved in water is 

The equation for a chemical reaction does not provide enough information to enable you to carry out the reaction in a laboratory or chemical plant. An important aspect of modern chemical research involves working out the conditions for a reaction. The reaction conditions are often written above or below the arrow in an equation. For example, the Greek capital letter delta. A, means that a high temperature is required—that is, the reaction mixture must be heated, as in the decomposition of silver oxide. 

An even more explicit statement of reaction conditions is shown below for the BASF (Badische Anilin Soda-Fabrik) process for the synthesis of methanol from CO and H2. This reaction occurs at 350 °C, under a total gas pressure that is 340 times as great as the normal pressure of the atmosphere, and on the surface of a mixture of ZnO and Cr203 acting as a catalyst. As we will learn later in the text, a catalyst is a substance that enters into a reaction in such a way that it speeds up the reaction without itself being consumed or changed by the reaction. 

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