12 Matching Annotations
  1. Jun 2020
    1. Theoretical Yields When reactants are not present in stoichiometric quantities, the limiting reactant determines the maximum amount of product that can be formed from the reactants. The amount of product calculated in this way is the theoretical yield, the amount obtained if the reaction occurred perfectly and the purification method were 100% efficient. In reality, less product is always obtained than is theoretically possible because of mechanical losses (such as spilling), separation procedures that are not 100% efficient, competing reactions that form undesired products, and reactions that simply do not run to completion, resulting in a mixture of products and reactants; this last possibility is a common occurrence. Therefore, the actual yield, the measured mass of products obtained from a reaction, is almost always less than the theoretical yield (often much less). The percent yield of a reaction is the ratio of the actual yield to the theoretical yield, multiplied by 100 to give a percentage: percent yield=actual yield (g)theoretical yield(g)×100%(3.7.29)
    1. What happens to matter when it undergoes chemical changes? The Law of conservation of mass says that "Atoms are neither created, nor distroyed, during any chemical reaction." Thus, the same collection of atoms is present after a reaction as before the reaction. The changes that occur during a reaction just involve the rearrangement of atoms.
    2. 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 3.1.23.1.2\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 3.1.43.1.4\ref{3.1.3}). Equation 3.1.43.1.4\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 3.1.33.1.3\PageIndex{3}. Figure 3.1.33.1.3\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. Mar 2019
    1. This page describes a method of teaching designed specifically for adults. The instructional design theory is Keller's "ARCS," which stands for attention, relevance, confidence, and satisfaction--all features that adult learning experiences should be characterized by. The text on this page is readable but the popups and graphics are a bit annoying. rating 3/5

  3. Dec 2016
    1. al telephone.

      Helen Keller was associates with important such as Alexander Graham bell and President Roosevelt.

    1. Not was Helen Keller the face for the AFB but she was also a national leader for the socialist party. This info shows that she was a big part of the 20th century not only for disabled but for everyone else as well.

    1. People who are deaf-blind have marketable skills and strategies to compete and succeed in the workplace.

      Just because people have disables doesn't mean that they have to be discriminated on, Helen Keller started a revolution for improving the life for people that are deaf or blind.

    2. Helen Keller National Center for Deaf-Blind Youths & Adults

      Helen Keller's achievements in creating many foundations were celebrated around the world to recognize the achievements of many blind and deaf people.

    1. resolved

      There was a fire lit underneath her when she found out that she could learn to speak and she went ahead and learned French German and english.

  4. Jan 2016
    1. Getting and staying healthy involves tending to the people-oriented aspects of leading an organization, so it may sound “fluffy” to hard-nosed executives raised on managing by the numbers. But make no mistake: cultivating health is hard work. And it shouldn’t be confused with other people-related management concepts, such as employee satisfaction or employee engagement.

      I am looking forward to what these authors will provide as a recipe for cultivating health, and how they define organizational health.