Chemical Reactions Let's start with the idea of a reaction. In chemistry, a reaction happens when two or more molecu

1. Chemical Reactions Let's start with the idea of a reaction. In chemistry, a reaction happens when two or more  molecules interact and something happens. That's it. What molecules are they? How do they interact? What happens?

2. Those are all the possibilities in reactions. The possibilities are infinite. There are a few key points you should know about chemical reactions.  Key Points 1. A chemical change must occur. You start with one compound and turn it into another. That's an example of a chemical change. • A steel garbage can rusting is a chemical reaction • When a refrigerator or air conditioner cools the air, there is no reaction.

3. That rusting happens because the iron (Fe) in the metal combines with oxygen (O2) in the atmosphere. • That change in temperature is a physical change. Nevertheless, a chemical reaction can happen inside of the air conditioner.  2. A reaction could include ions, molecules, or pure atoms We said molecules in the previous paragraph, but a reaction can happen with anything, just as long as a chemical change occurs (not a physical one).

4. If you put pure hydrogen gas (H2) and pure oxygen gas in a room, they can be involved in a reaction. The slowrate of reactionwill have the atoms bonding to form water very slowly

5. If you were to add a spark, those gases would create a reaction that would result in a huge explosion. Chemists would call that spark a catalyst.

6. 3. Single reactions often happen as part of a larger series of reactions. Take something as simple as moving your arm. The contraction of that muscle requires sugars or energy. Those sugars need to be metabolized. You'll find that proteins need to move in a certain way to make the muscle contract. A whole series (hundreds actually) of different reactions are needed to make that simple movement happen.

7. What chemical reactions do you conduct every morning? • Brushing your teeth • Eating breakfast • Getting a ride to school The fluoride compounds in your toothpaste react with compounds in your teeth to produce new harder compounds that can resist decay. Acids and other chemicals in your digestive system react with food to produce the nutrients that your body needs. Hydrocarbons in the fuel that powers the family car react with oxygen from the air to produce new gas molecules and energy

8. Chemical reactions are also used to make many of the chemical compounds that are part of our lives • the plastic containers that hold your lunch • the synthetic fibres used to make some of your clothes have been made by the chemical industry. • when you get a bacterial infection, the antibiotics that the doctor may prescribe are products of the pharmaceutical industry. • children’s toys, whether dolls, in-line skates are almost all made of synthetic products.

9. How do chemical reactions happen? How do chemists categorize the thousands of different chemical reactions? We have talked about how chemical compounds can be categorized as ionic or molecular. With this knowledge, it will help you understand and predict different types of chemical reactions.

10. Chemical reactions may involve sophisticated chemicals, as in the explosive reaction of dynamite, or simple household materials, as in the reaction of a bathroom cleaner with a stain The may occur constantly as in the growth of your body Or occasionally, as in the changing colour of leaves in fall. How can you describe such a wide range of reactions? A word equation

11. A word equation is a way of representing a chemical reaction: it tells you what reacts and what is produced. It is an efficient way to describe chemical changes. A word equation is a summary of a chemical reaction : It uses words to indicate what reacts and what is produced How do we write them?

12. Writing Word Equations Word equations are written in a particular format. The left side of a word equation lists the names of all reactants( the substances present initially) The right side lists the names of all the products (the substances present at the end) An arrow points from the reactants to the products

13. all the reactants all the products The reactants, as well as the products, are separated by a plus sign (+): reactant 1 + reactant 2 product 1 + product 2

14. Word Equations for Some Chemical Reactions You know that the rusting of iron is a slow process– it takes a car a long time to rust. However when hot steel wool (iron) is plunged into a bottle of oxygen, a spectacular chemical reaction occurs. The reactants are iron and oxygen, and the product is iron (III) oxide. iron + oxygen iron(III) oxide

15. The reaction that occurs when a coil of copper is placed in a beaker of colourless silver nitrate solution is represented by: copper + silver nitrate silver + copper (II) nitrate

16. All chemical reactions can be represented by word equations. For example, when zinc metal is added to a hydrochloric acid solution, a flammable gas and a and a colourless solution result. zinc + hydrochloric acid hydrogen + zinc chloride

17. In a chemical test for hydrogen, the gas “pops” as it reacts explosively with oxygen from the air: hydrogen + oxygen water vapour

18. Chemists use word equations to summarize what they observe. Copy and complete the word equations that describe the following observations a) Aluminum resists corrosion because it reacts with a gas found in air to form a protective coating of aluminum oxide. b) Zinc metal, used as a coating in galvanized iron, also reacts with air to form a coating that resists further corrosion

19. c) When aluminum foil is placed in a solution of copper (II) chloride, copper metal and another solution are formed d) When sodium sulfate and calcium chloride solutions are mixed, a precipitate of calcium sulfate and another substance is formed.

20. What is matter? Can matter be destroyed? What happens if a forest is burned? Is matter destroyed?

21. Scientists found a way to trap gases that were produced in chemical reactions. After years of experimenting they agreed that mass is neither created nor lost in a chemical reaction This conclusion is stated as a law.

22. A scientific law is a general statement that sums up the conclusions of many experiments. The Law of Conservation of Mass The Law states that , in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products What does it tell us about the atoms that make up the reactants and products?

23. Experiments have shown that atoms in a chemical reaction are not changed the number of each kind of atom is the same before and after a reaction. In chemical reactions, the atoms of the reactants are simply rearranged.

24. Let’s look at the burning of methane or natural gas. methane + oxygen water + carbon dioxide Demonstration

25. Copper sulfate solution with sodium hydroxide solution a copper hydroxide precipitate forms A precipitate is a solid that may form when two compounds in solution react with each other. copper (II) sulfate (aq) + sodium hydroxide copper(II) hydroxide(aq) + sodium sulfate (aq) We use abbreviations to identify the states of substances The symbol (aq) represents the term aqueous , which means dissolved in water. (l) (s) (g) Review how to count atoms

26. How do scientists in different countries, speaking different languages communicate the results of their experiments to each other? Word equation Skeleton equation Example: methane(g) + oxygen(g) carbon dioxide(g) + water(l) CH4(g) + O2(g) CO2(g) + H2O(l) However, there is a problem

27. What does the law of conservation of mass say? In other words atoms cannot be created nor destroyed How do we resolve this problem? By balancing the chemical equation

28. Balancing Equations: Chemical

29. Cl2 2Cl 2Cl2 • Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2 • Notice that the OH is a group • The 2 refers to both H and O • How many of each atom are in the following? • a) NaOH • b) Ca(OH)2 • c) 3Ca(OH)2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

30. Mg Mg O O O  + Balancing equations: MgO • The law of conservation of mass states that matter can neither be created or destroyed • Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction • Thus, the number of a particular atom is the same on both sides of a chemical equation • Example: Magnesium + Oxygen • Mg + O2 MgO • However, this is not balanced • Left: Mg = 1, O = 2 • Right: Mg = 1, O = 1

31. How to Balance an Equation Let’s look at an example. Iron reacts with oxygen to form magnetic oxide (Fe3O4). What is the balanced chemical equation for this reaction? Step 1: Write the word equation for the reaction? iron + oxygen magnetic iron oxide Step 2: write the skeleton equation by replacing each name with the correct formula Fe + O2 Fe3O4

32. Step 3: Count the number of atoms of each type in reactants and products. Step 4: Multiply each of the formulas by the appropriate coefficients to balance the numbers of atoms 3Fe + 2O2 Fe3O4

33. A balanced chemical equation has been written. The formulas are unchanged, and the number of atoms are balanced. What is the balanced chemical equation for the reaction of magnesium metal and with nitric acid? Step 1: write the word equation for the reaction magnesium + nitric acid hydrogen + magnesium nitrate Step 2: Write the skeleton equation by replacing each name with the correct formula Mg + HNO3 H2 + Mg(NO3)2

34. Step 3: Count the numbers of atoms of each type in reactants and products. Step 4: multiply each of the formulas by the appropriate coefficients to balance the numbers of atoms Mg + 2HNO3(aq) H2 + Mg(NO3)2