Chemical Formulas and Equations

When considering chemical reactions—including explosions—it is often handy to think in terms of the microscopic, macroscopic, and symbolic perspectives introduced in Section 1.2. Now we will develop these ideas further in the specific context of reactions and explosions. 

Although the properties and uses of different explosives vary considerably, all involve chemical reactions. A realistic description of the chemistry of virtually any explosion would require us to consider many individual reactions. To discuss the science behind an explosion, we must be able to describe a chemical reaction concisely. In Chapter 2, weVe already seen how chemical formulas provide a concise way to represent chemical compounds, and we will now describe how chemical equations build on this to accomplish the same goal for chemical reactions. 

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We use this information, and our knowledge of writing chemical formulas and equations, to write the balanced chemical equation ... 

Steenberg E (2006) Investigation of the development of bridging students cognitive skills relevant to the use and understanding of chemical formulae and equations. Unpubhshed MSc (Science Ed) thesis, University of South Africa. 

There are ample self-made misconceptions regarding the formulation of reaction symbols. Mulford and Robinson [32] discovered the following situations regarding questions 5 and 6 (see Fig. 5.21) when evaluating the empirical studies Responses to question 5 suggest that students came to us with a very poor understanding of chemical formulas and equations. Only 11 % selected the correct answer d. When we consider the number of students who selected responses a, c and e, we see that 65% chose responses that do not conserve atoms. Combining responses a, b and e indicates that 74% appear not to understand the difference between the coefficient 2 and the subscript 3 in 2 S03 [32],... 

Chemical stoichiometry is the area of study that considers the quantities of materials in chemical formulas and equations. Quite simply, it is chemical arithmetic. The word itself is derived from stoicheion, the Greek word for element and metron, the Greek word for measure. When based on chemical formulas, stoichiometry is used to convert between mass and moles, to calculate the number of atoms, to calculate percent composition, and to interpret the mole ratios expressed in a chemical formula. Most topics in chemical arithmetic depend on the interpretation of balanced chemical equations. Mass/mole conversions, calculation of limiting reagent and percent yield, and various relationships among reactants and products are commonly included in this topic area. 

We use the quantitative information inherent in chemical formulas and equations together with the mole concept to predict the amounts of substances consumed or produced in chemical reactions. 

CHAPTER 3 Stoichiometry Calculations with Chemical Formulas and Equations... 

Chemical formulas and chemical equations both have a quantitative significance in that the subscripts in formulas and the coefficients in equations represent precise quantities. The formula H2O indicates that a molecule of this substance (water) contains exactly two atoms of hydrogen and one atom of oxygen. Similarly, the coefficients in a balanced chemical equation indicate the relative quantities of reactants and products. But how do we relate the numbers of atoms or molecules to the amounts we measure in the laboratory Although we cannot directly count atoms or molecules, we can indirectly determine their numbers if we know their masses. Therefore, before we can pursue the quantitative aspects of chemical formulas and equations, we must examine the masses of atoms and molecules. 

Chemistry is by nature an abstract subject. First, it relies on a symbolic language based on chemical formulas and equations. Second, it is based on the behavior of atoms and molecules—particles far too small to see. By presenting chemistry visually, the authors help you to "see" the chemistry you need to learn and increase your success in the course. 

Knowledge of symbols is essential for writing chemical formulas and equations, and will be needed in the remainder of this book and in any future chemistry courses you may take. One way to learn the symbols is to practice a few minutes a day by making flash cards of names and symbols and then practicing daily. Initially, it is a good plan to learn the symbols of the most common elements shown in Table 3.3. 

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