Using chemical equations

The chemical principles discussed in this book are often illustrated using equations. It is useful to know a few of the ground rules chemists have adopted to construct these. Let us begin by looking at an equation depicting the process of rusting metallic iron  

Firstly, the arrow shows that the reaction is favoured in one direction (we will demonstrate this later when discussing energy needed to drive reactions). Next we can see that the reaction balances, i.e. we have four atoms of iron and six atoms of oxygen on both sides of the equation. When chemical reactions take place, we neither gain nor lose atoms. Finally, the subscripted characters in brackets represent the status of the chemical species. In this book 1 = liquid, g = gas, s = solid and aq = an aqueous species, i.e. a component dissolved in water. 

It is important to realize that these reactions are usually simplifications of the actual chemical transformations that occur in nature. In equation 2.6 we are representing rusted or oxidized iron as Fe203, the mineral haematite. In nature, rusted metal is a complex mixture of iron hydroxides and water molecules. So equation 2.6 summarizes a series of complicated reaction stages. It illustrates a product we might reasonably expect to form without necessarily depicting the stages of reaction or the complexity encountered in nature. 

Many of the equations in this book are written with the reversible reaction sign (two-way half-arrows e.g. eqn. 2.5). This shows that the reaction can proceed in either direction and this is fundamental to equilibrium-based chemistry (see Box 3.2). Reactions depicting dissolution of substances in water may or may not show the water molecule involved, but dissolution is implied by the (aq) status symbol. Equation 2.7, read from left to right, shows dissolution of rock salt (halite). 

The reverse reaction (right to left) shows crystallization of salt from solution. 

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Using chemical equations, illustrate how soil carbon dioxide affects both the pH of soil and the ions present in the soil solution. 

Represent one example of a galvanic cell, and one example of an electrolytic cell, using chemical equations, half-reactions, and diagrams. 

In the end, chemistry is about action — about the breaking and making of bonds. Chemists describe action by using chemical equations, sentences that say who reacted with whom and who remained when the smoke cleared. This chapter explains how to read, write, balance, and predict the products of these action-packed chemical sentences. 

Outline processes, using chemical equations where possible, by which (a) titantium and (b) vanadium are prepared. 

Use chemical equations to show how the following accidents cause injury to the clothing involved (not to mention the skin under the clothing ). 

For example, when the glucose in a marshmallow reacts with oxygen in the air to form water and carbon dioxide, the glucose and oxygen are the reactants. The carbon dioxide and water are the products. Chemists use chemical equations to communicate what is occurring in a chemical reaction. Chemical equations come in several forms. All of these forms condense a great deal of chemical information into a short statement. 

Titration of NH4CI with SnCl4 in ICl requires 2 moles of NH4CI for every mole of SnCl4 to reach the endpoint. Explain, using chemical equations. 

Outline, using chemical equations, the synthesis of the following from easily available petrochemicals and inorganic starting materials. 

A saturated aqueous solution of silver perchlorate (AgC104) contains 84.8% by mass AgC104, but a saturated solution of AgC104 in 60% aqueous perchloric acid contains only 5.63% by mass AgC104. Explain this large difference using chemical equations. 

We are now ready to use chemical equations to calculate the relative amounts of substances involved in chemical reactions. Let us again consider the combustion of methane in excess oxygen. The balanced chemical equation for that reaction is... 

Use chemical equations to illustrate the hydroxides of beryllium, zinc, arsenic, and antimony reacting (a) as acids (b) as bases. 

Use chemical equations to show that the buffer system in blood works like the buffer in question 1. 

Having discussed the masses of atoms and molecules, we turn next to what happens to atoms and molecules in a chemical reaction, a process in which a substance (or substances) is changed into one or more new substances. In order to communicate with one another about chemical reactions, chemists have devised a standard way to represent them using chemical equations. A chemical equation uses chemical symbols to show what happens during a chemical reaction. In this section we will learn how to write chemical equations and balance them. 

How can the Diels-Alder reactions be carried out with unsaturated polymers Use chemical equations to illustrate. 

Describe the reactions of sodium azide with poly(vinyl chloride) and the subsequent reactions of the azide group. Use chemical equations. 

The third way that chemists perceive their subject is to use symbols to represent the atoms, molecules, and reactions that make up the science. We will wait to introduce this perspective in detail in the next two chapters—but here we point out that you certainly have encountered chemical symbols in your previous studies. The famous H two O molecule we have noted is never depicted as we have done here in the quotation marks. Rather, you have seen the symbolic representation of water, H2O. In Chapter 2, we will look at chemical formulas in more detail and in Chapter 3, we will see how we use them to describe reactions using chemical equations. For now, we simply note that this symbolic level of understanding is very important because it provides a way to discuss some of the most abstract parts of chemistry. We need to think about atoms and molecules, and the symbolic representation provides a convenient way to keep track of these particles we ll never acmally see. These symbols will be one of the key ways that we interact with ideas at the particulate level. 

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