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In a mslsec.comical change, new substances are formed. In order for this to occur, the mslsec.comical bonds of the substances break, and the atoms that compose them separate and rearrange themselves into new substances with new mslsec.comical bonds. When this process occurs, we call it a mslsec.comical reaction. A mslsec.comical reaction is the process in which one or more substances are changed into one or more new substances.
Reactants and Products
To describe a mslsec.comical reaction, we need to indicate what substances are present at the beginning and what substances are present at the end. The substances that are present at the beginning are called reactants and the substances present at the end are called products.
Sometimes when reactants are put into a reaction vessel, a reaction will take place to produce products. Reactants are the starting materials, that is, whatever we have as our initial ingredients. The products are just that—what is produced—or the result of what happens to the reactants when we put them together in the reaction vessel. If we think about baking chocolate chip cookies, our reactants would be flour, butter, sugar, vanilla, baking soda, salt, egg, and chocolate chips. What would be the products? Cookies! The reaction vessel would be our mixing bowl.
< underbrace extFlour + extButter + extSugar + extVanilla + extBaking Soda + extEggs + extChocolate Chips_ extIngredients = Reactants ightarrow underbrace extCookies_ extProduct onumber>
Writing mslsec.comical Equations
When sulfur dioxide is added to oxygen, sulfur trioxide is produced. Sulfur dioxide and oxygen, (ceSO_2 + ceO_2), are reactants and sulfur trioxide, (ceSO_3), is the product.
< underbracece2 SO2(g) + O2(g) _ extReactants ightarrow underbracece2SO3(g)_ extProducts onumber>
In mslsec.comical reactions, the reactants are found before the symbol "( ightarrow)" and the products are found after the symbol "( ightarrow)". The general equation for a reaction is:
< extReactants ightarrow extProducts onumber>
There are a few special symbols that we need to know in order to "talk" in mslsec.comical shorthand. In the table below is the summary of the major symbols used in mslsec.comical equations. Table (PageIndex1) shows a listing of symbols used in mslsec.comical equations.
|(+)||used to separate multiple reactants or products||(left( s ight))||reactant or product in the solid state|
|( ightarrow)||yield sign; separates reactants from products||(left( l ight))||reactant or product in the liquid state|
|( ightleftharpoons)||replaces the yield sign for reversible reactions that reach equilibrium||(left( g ight))||reactant or product in the gas state|
|(oversetcePt ightarrow)||formula written above the arrow is used as a catalyst in the reaction||(left( aq ight))||reactant or product in an aqueous solution (dissolved in water)|
|(oversetDelta ightarrow)||triangle indicates that the reaction is being heated|
mslsec.comists have a choice of methods for describing a mslsec.comical reaction.
1. They could draw a picture of the mslsec.comical reaction.
2. They could write a word equation for the mslsec.comical reaction:"Two molecules of hydrogen gas react with one molecule of oxygen gas to produce two molecules of water vapor."
3. They could write the equation in mslsec.comical shorthand.
<2 ceH_2 left( g ight) + ceO_2 left( g ight) ightarrow 2 ceH_2O left( g ight)>
In the symbolic equation, mslsec.comical formulas are used instead of mslsec.comical names for reactants and products, while symbols are used to indicate the phase of each substance. It should be apparent that the mslsec.comical shorthand method is the quickest and clearest method for writing mslsec.comical equations.
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We could write that an aqueous solution of calcium nitrate is added to an aqueous solution of sodium hydroxide to produce solid calcium hydroxide and an aqueous solution of sodium nitrate. Or in shorthand we could write:
How much easier is that to read? Let"s try it in reverse.Look at the following reaction in shorthand and write the word equation for the reaction:
The word equation for this reaction might read something like "solid copper reacts with an aqueous solution of silver nitrate to produce a solution of copper (II) nitrate with solid silver."
To turn word equations into symbolic equations, we need to follow the given steps:Identify the reactants and products. This will help you know whichsymbols go on each side of the arrow and where the (+) signs go. Write the correct formulas for all compounds. You will need to use the rules you learned in Chapter 5 (including making all ionic compounds charge balanced). Write the correct formulas for all elements. Usually this is given straight off of the periodic table. However, there are seven elements that are considered diatomic, meaning that they are always found in pairs in nature. They include those elements listed in the table.