At 4 minutes the temperature in the flask was about 23ºC. The first time the temperature was 6ºC was at about 7 minutes. Reading Graphs: What was the temperature in the flask at 4 minutes? When was the first time the temperature was at 6ºC? - Observing Chemical Change Energy in Chemical Changes

20ºC Calculating: How many degrees did the temperature drop between2 minutes and 5 minutes? - Observing Chemical Change Energy in Chemical Changes

The reaction was endothermic; it absorbed thermal energy from the reaction mixture, causing the temperature to drop. Interpreting Data: Is the reaction endothermic or exothermic? Explain. - Observing Chemical Change Energy in Chemical Changes

The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached. Inferring: At what temperature did the reaction stop? How can you tell? - Observing Chemical Change Energy in Chemical Changes

If the temperature increased, the reaction would be exothermic; an exothermic reaction is one in which energy is released. Drawing Conclusions: Suppose the temperature in the flask increased instead of decreased as the reaction occurred. In terms of energy, what kind of reaction would it be? Explain. - Observing Chemical Change Energy in Chemical Changes

- Observing Chemical Change Asking Questions • Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions. Properties and Changes of Matter Question Answer What are physical properties of matter? Physical properties are characteristics that can be observed without changing one substance into another. What is the evidence for chemical reactions? The evidence for chemical reactions is the formation of new substances and changes in energy.

- Observing Chemical Change Links on Chemical Changes • Click the SciLinks button for links on chemical changes.

End of Section:Observing Chemical Change

- 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.

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

- 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.

- 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.

- 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.

- Describing 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 Balancing Chemical Equations • Magnesium metal (Mg) reacts with oxygen gas (O2), 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.

Balancing Chemical Equations: Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O). - Describing Chemical Reactions Balancing Chemical Equations

Balancing Chemical Equations: Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2). - Describing Chemical Reactions Balancing Chemical Equations

- Describing Chemical Reactions Classifying Chemical Reactions • Many chemical reactions can be classified in one of three categories: synthesis, decomposition, or replacement.

Key Terms: Key Terms: Examples: Examples: closed system replacement coefficient synthesis decomposition - Describing 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. Key Terms: Examples: chemical equation A chemical equation is a short, easy way to show a chemical reaction. In a closed system, matter is not allowed to enter or leave. Replacement is the process in which one element replaces another in a compound or two elements in different compounds trade places. reactant A substance you have at the beginning of a reaction is a reactant. 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. product A new substance produced in a reaction is a product. Synthesis means combining two or more elements or compounds to make a more complex substance. conservation of mass Conservation of mass means that during a chemical reaction, matter is not created or destroyed. open system In an open system, matter can enter from or escape to the surroundings. Decomposition means breaking down compounds into simpler products.

End of Section:Describing Chemical Reactions

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

- Controlling Chemical Reactions Energy and Reactions • Both exothermic and endothermic reactions need energy to get started.

- 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.

- Controlling 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. Causes Increase in surface area Effect Increase in temperature Increased rate of reaction Increase in concentration of reactants Use of a catalyst

Data Sharing Lab • Click the PHSchool.com button for an activity about sharing data for the Skills Lab Temperature and Enzyme Activity.

- Controlling Chemical Reactions Exothermic and Endothermic Reactions • Click the Video button to watch a movie about exothermic and endothermic reactions.

End of Section:Controlling Chemical Reactions

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

- 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.

- Fire and Fire Safety Home Fire Safety • If you know how to prevent fires in your home and what to do if a fire starts, you are better prepared to take action.

- Fire and Fire Safety Using Prior Knowledge • Before you read, write what you know about fire safety in a graphic organizer like the one below. As you read, write what you learn. What You Know A fire needs fuel to burn. A fire need oxygen to burn. All homes should have smoke detectors. What You Learned Fire is a result of a combustion reaction. The most deadly fires start with cigarettes. Baking soda can be used to put out small fires.

- Fire and Fire Safety Links on Fire Safety • Click the SciLinks button for links on fire safety.

End of Section:Fire and Fire Safety

Graphic Organizer Chemical reactions can be are written as Endothermic reactions Exothermic reactions Equations balanced with which require written using Coefficients Activation energy Chemical symbols Arrows and plus signs

End of Section:Graphic Organizer

Table of Contents