2 Matching Annotations
  1. Jun 2020
    1. C7H16(l)+O2(g)→CO2(g)+H2O(g)(3.1.4)(3.1.4)C7H16(l)+O2(g)→CO2(g)+H2O(g) C_7H_{16} (l) + O_2 (g) \rightarrow CO_2 (g) + H_2O (g) \label{3.1.3} The complete combustion of any hydrocarbon with sufficient oxygen always yields carbon dioxide and water. Figure\PageIndex{2}: An Example of a Combustion Reaction. The wax in a candle is a high-molecular-mass hydrocarbon, which produces gaseous carbon dioxide and water vapor in a combustion reaction (see Equation\ref{3.1.3}). Equation\ref{3.1.3} is not balanced: the numbers of each type of atom on the reactant side of the equation (7 carbon atoms, 16 hydrogen atoms, and 2 oxygen atoms) is not the same as the numbers of each type of atom on the product side (1 carbon atom, 2 hydrogen atoms, and 3 oxygen atoms). Consequently, the coefficients of the reactants and products must be adjusted to give the same numbers of atoms of each type on both sides of the equation. Because the identities of the reactants and products are fixed, the equation cannot be balanced by changing the subscripts of the reactants or the products. To do so would change the chemical identity of the species being described, as illustrated in Figure\PageIndex{3}. Figure\PageIndex{3}: Balancing Equations. You cannot change subscripts in a chemical formula to balance a chemical equation; you can change only the coefficients. Changing subscripts changes the ratios of atoms in the molecule and the resulting chemical properties. For example, water (H2O) and hydrogen peroxide (H2O2) are chemically distinct substances. H2O2 decomposes to H2O and O2 gas when it comes in contact with the metal platinum, whereas no such reaction occurs between water and platinum. The simplest and most generally useful method for balancing chemical equations is “inspection,” better known as trial and error. The following is an efficient approach to balancing a chemical equation using this method.
  2. Apr 2020
    1. I'm not your personal lookup service And finally, for everyone who contacts me privately and says "but could you just look up my own password", please understand that you're one of many people who ask this. I try and reply to everyone who asks and politely refer them to my previous writing on the subject, but even then, all the time I spend replying to these requests is time I can't spend building out the service, adding more data, earning a living doing other things or spending time with my family. For the last 3 and a half years that I've run HIBP, I've kept all the same features free and highly available as a community service. I want to keep it that way but I have to carefully manage my time in order to do that so in addition to all the reasons already stated above, no, I'm not your personal lookup service.