Chapter 3- Types of Chemical reactions.pptx

Chapter 3- Types of Chemical reactions  3.1 Word Equations Chemical reactions can be simple (like powering a space shuttle) or complex (like taking an antacid). Chemical changes can be obvious (like burning a candle) or less the noticeable (like the reaction that makes a cak...

Chapter 3- Types of Chemical reactions  3.1 Word Equations Chemical reactions can be simple (like powering a space shuttle) or complex (like taking an antacid). Chemical changes can be obvious (like burning a candle) or less the noticeable (like the reaction that makes a cake rise). They can occur immediately (like explosives) or more slowly (like the ripening of a banana). To describe these many different chemical reactions, chemists often use a word equation  uses words to indicate what changed during the chemical reaction and what is produced Writing Word Equations Word equations are always written in the same format. The left side of the equation lists all the reactants. The right side of the equation lists all the products. An arrow points from the reactants to the products. It shows that something is produced during the reaction All the reactants and all the products in a word equation are separated by a plus sign (+). Word Equations for Some Chemical Reactions 1) cellular respiration oxygen + food (glucose)  carbon dioxide + water + energy The equation is read as: Oxygen and food (glucose) produce carbon dioxide and water and energy. 2) a common chemical reaction that produces limestone caves: carbonic acid + calcium carbonate  calcium hydrogen carbonate This equation is read as: Carbonic acid and calcium carbonate produce calcium hydrogen carbonate. 3) Hydrochloric acid to mossy zinc zinc + hydrochloric acid  zinc chloride + hydrogen gas + energy This equation is read as: Zinc and hydrochloric acid produce zinc chloride and hydrogen gas and energy. 3.2 Types of Reactions chemists know there are patterns in the way certain elements and compounds go together. They use these patterns to group different types of chemical reactions. Grouping chemical reactions is useful for several reasons, it allows chemists to predict the product of an unknown chemical reaction It helps them to understand the behaviour of substances in a chemical reaction. Four most common reaction types 1) Simple Composition Reactions two or more simple elements combine to form a compound. Whenever you see two elements as reactants, you know that the reaction is a simple composition reaction the product is always a compound. Element l + Element 2  Compound A + B  AB most simple ,composition reactions are exothermic  some form of energy is released 2) Simple Decomposition Reactions A reaction that breaks a compound into its component elements Whenever you see a compound as the only reactant, you know the reaction is a simple decomposition reaction electrolysis, water is broken down into hydrogen gas and oxygen gas. Electric energy is needed to drive this reaction. Compound  Element 1 + Element 2 AB  A + B Most decomposition reactions are endothermic, meaning that energy is absorbed. 3) Combustion Reactions When you light a candle, the candle wax burns in the presence of oxygen to produce carbon dioxide and water. Combustion always occurs in the presence of oxygen The word equation for the combustion of gasoline (octane) is: gasoline (octane) + oxygen  carbon dioxide + water vapour + energy butane butane + oxygen  carbon dioxide + water vapour + energy Oil and natural gas are fossil fuels  they come from the accumulated remains of plants and animals from prehistoric times. Did You Know? 76 L of petroleum can provide the gasoline to drive a vehicle 485 km can produce 24 shirts, 5 m2 of carpeting material, 2 automobile tires, 30 m of 1.3 cm diameter rope, 12 windbreakers, 2 tents, 4 sleeping bags, 6 duffel bags, 1 blanket, 4 sweaters, 15 parkas 4) Neutralization Reactions In a neutralization reaction, an acid reacts with a base to produce a form of salt and water. The word equation for a neutralization reaction is: acid + base  salt + water When you take an antacid, the magnesium hydroxide in the tablet reacts with the hydrochloric acid in your stomach. This neutralization reaction is written as: hydrochloric acid + magnesium hydroxide  magnesium chloride+ water  3.3Formulas for Common Compounds Chemical Names and Formulas add zinc powder to sulfur powder and then apply heat. The word equation for this reaction is: sulfur + zinc  zinc sulfide When you write a word equation like this, you are using what is known as the chemical name for each of the reactants and products  the periodic table  has the chemical names of all the elements along with their chemical symbols. Each element has a symbol that consists of one capital letter or one capital and one lower-case letter. In this example, you have sulfur (S) and zinc (Zn).  Information about the chemical composition and structure of a compound is given by its chemical formula. In the above example, the product is the compound zinc sulfide, which has the chemical formula ZnS. The rule for naming compound; like this is ex. ZnS 1) to name the metal first - zinc 2) followed by the name of the non-metal 3)The name of the non-metal is changed to "ide"- sulfide. You could now replace the names of the reactants with their used the following ( chemical symbols, and the product with its chemical formula. When writing formulas, remember to use a subscript to indicate the state of the material. In this example, we are dealing with solids, which are shown as (s)' The chemical equation would look like this: S8(s) + 8Zn(s)  8ZnS(s) (s) to indicate a solid (l) to indicate a liquid (g) to indicate a gas Common Names Not everyone is a scientist, so many chemical compounds are often identified by a common name. These names are easier to use, and they have existed since before the international naming system was created  3.4 Chemical Equations The Law of Conservation of Mass In a chemical reaction, matter is not created or destroyed. If you start a reaction with 10 g of reactants, you will end up with 10 g of products. solid mercury (II) oxide  oxygen gas + liquid mercury 10.0 g 0.7 g 9.3 g Staying Balanced When chemists write chemical equations, they do not usually use word equations. When dealing with chemicals, this method is not exact enough. They need to know the exact quantities of chemicals to use when chemical reactions are used in technological processes. Word equations do not state the quantities of the substances needed. vinegar + baking soda sodium acetate + water + carbon dioxide gas When the chemical formulas of the reactants and products are used, then you can determine exactly what atoms make up the reactants and products.  Checking the Balance of Simple Equations A balanced chemical equation has the same elements and the same number of atoms of each element on both sides. Steps in Solving It 1. What elements are on the reactant side? 2. How many atoms of each element are on the reactant side? 3. What elements are on the product side? 4. How many atoms of each element are on the product side? 5. Is this equation balanced?  Example C(s) + 02(g)  CO2(g) 1. What elements are on the reactant side? C is the element carbon. O is the element oxygen. 2. How many atoms of each element are on the reactant side? There is no subscript beside carbon. This means that there is only one atom of carbon. The subscript 2 expressed as (2) beside oxygen tells you there are 2 atoms of oxygen. 3. What elements are on the product side? there is a C and an 0. 4. How many atoms of each element are on the product side? There is no subscript with C, so there is only one atom of carbon. O has a subscript 2. So there are two atoms of oxygen. 5. Is this equation balanced? reactant side = 1 atom of carbon, 2 of oxygen product side = 1 atom of carbon, 2 of oxygen Yes, the equation is balanced. Try These Try These  Checking the Balance of Complex Equations 2H20(l)  02(g) + 2H2(g) In such equations, the numbers in front of the chemical formulas are called coefficients. Coefficients are used to balance those individual atoms. In 2H20(l)  02(g)+ 2H2(g) the 2 in front of the H is a coefficient. It tells how many H2 molecules are present. Identify and count the atoms on each side. Is it balanced? 2H20(l)  02(g) + 2H2(g) 1. What elements are on the reactant side? H and 0. They are hydrogen and oxygen. 2. How many atoms of each element are on the reactant side? The 2 in front of H2O(l) makes this tricky. The large 2 means that there are 2 H2 and 2 0. 2H2 = H2 + H2 The subscript 2 (2) beside hydrogen tells that there are two hydrogen atoms in each H2 molecule. H2 = H + H And there are two of these in the chemical name. So 2H2 = H + H + H + H = 4 hydrogen atoms 20 = O+ O = 2 oxygen atoms 3. What elements are on the product side? These are hydrogen and oxygen. 4. How many atoms of each element are on the product side? 02 = O + O The 2 in front of H2(g) makes this tricky. The large 2 means that there are 2 H2(g) Let's deal with each one separately. 2H2 = H2 + H2 The subscript 2 (2) beside hydrogen tells that there are two hydrogen atoms in each H2 molecule. H2 = H + H And there are two of these in the chemical name. So 2H2 = H + H + H + H = 4 hydrogen atoms 5. Is this equation balanced? reactant side = 2 oxygen atoms, 4 hydrogen atoms product side = 2 oxygen atoms, 4 hydrogen atoms Yes, the equation is balanced. Solve These