Chemical Reactions - Observing Chemical Change Properties and Changes in Matter Matter can undergo both physical change and chemical change.

Chemical Reactions - Observing Chemical Change Properties and Changes in Matter Chemical changes occur when bonds break and new bonds form.

Chemical Reactions - Describing Chemical Reactions Describing Chemical Reactions Cellular phone messages make use of symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.

Chemical Reactions - Describing Chemical Reactions What Are Chemical Equations? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Chemical Reactions - Describing Chemical Reactions Chemical Formulas The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

Chemical Reactions - Describing Chemical Reactions Conservation of Mass The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

Chemical Reactions - Describing Chemical Reactions Balancing Chemical Equations To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

Chemical Reactions Balancing Equations Activity Click the Active Art button to open a browser window and access Active Art about balancing equations. - Describing Chemical Reactions

Chemical Reactions Balancing Chemical Equations Magnesium metal (Mg) reacts with oxygen gas (O 2 ), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element. - Describing Chemical Reactions

Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O 2 ), forming sodium oxide (Na 2 O). - Describing Chemical Reactions

Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl 2 ), forming tin chloride (SnCl 2 ). - Describing Chemical Reactions

Chemical Reactions - Describing Chemical Reactions Classifying Chemical Reactions Many chemical reactions can be classified in one of three categories: synthesis, decomposition, or replacement. Synthesis: making larger molecules, ex: Photosynthesis Decompositition: Making smaller molecules, ex: Respiration Replacement: When one element replaces another. Ex: Zn + CuCl2 --> ZnCl2 + Cu

Chemical Reactions Building Vocabulary Using a word in a sentence helps you think about how best to explain the word. After you read the section, reread the paragraphs that contain definitions of Key Terms. Use the information you have learned to write a meaningful sentence using each Key Term. - Describing Chemical Reactions Key Terms:Examples: chemical equationA chemical equation is a short, easy way to show a chemical reaction. reactantA substance you have at the beginning of a reaction is a reactant. productA new substance produced in a reaction is a product. conservation of massConservation of mass means that during a chemical reaction, matter is not created or destroyed. open systemIn an open system, matter can enter from or escape to the surroundings. Key Terms:Examples: closed system coefficient synthesis decomposition In a closed system, matter is not allowed to enter or leave. A coefficient is a number in a chemical equation telling you how many atoms or molecules of a reactant or product take part in the reaction. Synthesis means combining two or more elements or compounds to make a more complex substance. Decomposition means breaking down compounds into simpler products. Key Terms:Examples: replacement Replacement is the process in which one element replaces another in a compound or two elements in different compounds trade places.

Chemical Reactions - Controlling Chemical Reactions Energy and Reactions All chemical reactions need a certain amount of activation energy to get things started.

Chemical Reactions - Controlling Chemical Reactions Energy and Reactions Both exothermic and endothermic reactions need energy to get started. A catalyst starts or speeds up a chemical reaction.

Chemical Reactions - Controlling Chemical Reactions Rates of Chemical Reactions The cells in your body (as in all living things) contain biological catalysts called enzymes. At the end of a reaction, an enzyme molecule is unchanged.

Chemical Reactions Relating Cause and Effect As you read, identify the factors that can cause the rate of a chemical reaction to increase. Write the information in a graphic organizer like the one below. Increased rate of reaction Increase in surface area Increase in temperature Increase in concentration of reactants Use of a catalyst Causes Effect - Controlling Chemical Reactions

Chemical Reactions - Fire and Fire Safety Understanding Fire Three things are necessary to start and maintain a fire–fuel, oxygen, and heat.

Chemical Reactions - Fire and Fire Safety Understanding Fire The fire triangle can be controlled in the grill. If any part of the fire triangle is missing, the fire will not continue.

Chemical Reactions Graphic Organizer Endothermic reactions Chemical reactions Exothermic reactions Equations Activation energy Chemical symbols Arrows and plus signs Coefficients can beare written as which requirewritten using balanced with