Table of Contents Chapter Preview 6.1 Observing Chemical Change 6.2 Describing Chemical Reactions 6.3 Controlling Chemical Reactions 6.4 Fire and Fire Safety

Chapter Preview Questions 1. Which of the following is an example of a physical change? a. Wood burns and becomes ash. b. A silver fork tarnishes. c. Water boils and becomes water vapor. d. Leaves decay over time.

Chapter Preview Questions 1. Which of the following is an example of a physical change? a. Wood burns and becomes ash. b. A silver fork tarnishes. c. Water boils and becomes water vapor. d. Leaves decay over time.

Chapter Preview Questions 2. When a forest burns, it a. neither absorbs nor releases energy. b. loses matter and energy. c. absorbs energy. d. releases energy.

Chapter Preview Questions 2. When a forest burns, it a. neither absorbs nor releases energy. b. loses matter and energy. c. absorbs energy. d. releases energy.

Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter Preview Questions 4. The ease and speed with which an element combines with other elements is called its a. atomic number. b. chemical property. c. physical property. d. reactivity.

Chapter Preview Questions 4. The ease and speed with which an element combines with other elements is called its a. atomic number. b. chemical property. c. physical property. d. reactivity.

What happens during a chemical reaction? Suppose you fill a sealable bag with ice cubes, and you allow the ice to melt. How would the mass of the bag and ice before melting compare to the mass of the water and the bag after melting? Explain your answer.

Identify Multiple Meanings Word Everyday Meaning Scientific Meaning concentration n. Close attention for a long period of time Example: Studying with the TV on affects her concentration. n. The amount of a substance in a given volume Example: Most soft drinks contain a high concentration of sugar.

Identify Multiple Meanings Word Everyday Meaning Scientific Meaning matter n. The subject of discussion, concern, or action Example: The subject matter of the movie was space travel. n. Anything that has mass and takes up space Example: Solids, liquids, and gases are states of matter.

Identify Multiple Meanings Word Everyday Meaning Scientific Meaning product n. Anything that is made or created Example: Milk and cheeses are dairy products. n. A substance formed as a result of a chemical reaction Example: In a chemical reaction, substances can combine to form one or more products.

Apply It! Complete the sentences below with the correct word from the list above. Then identify the terms that have scientific meanings. 1. The coach told the team to keep its during the game. concentration 2. Seawater has a high of salt. concentration (scientific meaning)

End of Chapter Preview

Section 1: Observing Chemical Change How can changes in matter be described? How can you tell when a chemical reaction occurs?

Properties and Changes in Matter Matter can undergo both physical change and chemical change.

Properties and Changes in Matter Chemical changes occur when bonds break and new bonds form.

Energy in Chemical Changes A student places two substances in a flask and measures the temperature once per minute while the substances react. The student plots the time and temperature data and creates the graph at left.

Energy in Chemical Changes Reading Graphs: What was the temperature in the flask at 3 minutes? When was the first time the temperature was at 6ºC? At 3 minutes the temperature in the flask was about 30ºC. The first time the temperature was 6ºC was at about 7 minutes.

Energy in Chemical Changes Calculating: How many degrees did the temperature drop between 2 minutes and 5 minutes? About 20ºC

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

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

Energy in Chemical Changes 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. If the temperature increased instead, the reaction would be exothermic, because an exothermic reaction is one in which energy is released.

Links on Chemical Changes Click the SciLinks button for links on chemical changes.

End of Section: Observing Chemical Change

Section 2: Describing Chemical Reactions What information does a chemical equation contain? How is matter conserved during a chemical reaction? What must a balanced chemical equation show? What are three types of chemical reactions?

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

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

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

Conservation of Matter The principle of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

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.

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

Balancing Chemical Equations Magnesium (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).

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

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

End of Section: Describing Chemical Reactions

Section 3: Controlling Chemical Reactions How is activation energy related to chemical reactions? What factors affect the rate of a chemical reaction?

Energy and Reactions All chemical reactions require a certain amount of activation energy to get things started.

Energy and Reactions Both exothermic and endothermic reactions need energy to get started.

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

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

End of Section: Controlling Chemical Reactions

Section 4: Fire and Fire Safety What are the three things necessary to maintain a fire? Why should you know about the causes of fire and how to prevent a fire?

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

Understanding Fire The fire triangle can be controlled in the grill. If any part of the fire triangle is missing, a fire will not continue.

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.

Click the SciLinks button for links on fire safety.

End of Section: Fire and Fire Safety

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