chapter 6 chemical reactionschapter 6 chemical reactions rates of chemical reactions the cells in...

Chapter 6 Chemical Reactions

Table of ContentsChapter 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.



2. When a forest burns, ita. neither absorbs nor releases energy.b. loses matter and energy.c. absorbs energy.d. releases energy.



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



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.


Suppose you fill a sealable bagwith ice cubes, and you allow theice to melt. How would the massof the bag and ice beforemelting compare to the mass ofthe water and the bag aftermelting? Explain your answer.

What happens during a chemical reaction?


Identify Multiple Meanings

Word Everyday Meaning Scientific Meaning

concentration

n. Close attention for a longperiod of time

Example: Studying with the TV on affects her concentration.

n. The amount of a substance in a givenvolume

Example: Most soft drinks contain a highconcentration of sugar.



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.




product

n. Anything that is made orcreated

Example: Milk and cheeses are dairy products.

n. A substance formed as a result of a chemical reaction

Example: In a chemical reaction, substancescan combine to form one or more products.



Apply It!

Complete the sentences below with the correct word from the listabove. 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

ChangeHow can changes in matter be described?How can you tell when a chemical reaction occurs?


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


Properties and Changes in MatterChemical 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.



At 3 minutes the temperature in the flask was about 30ºC. The first time the temperature was 6ºC was at about 7 minutes.

Reading Graphs:

What was the temperature in the flask at 3 minutes? When was the first time the temperature was at 6ºC?


Energy in Chemical ChangesCalculating:

How many degrees did the temperature drop between2 minutes and 5 minutes?

About 20ºC



The reaction was endothermic, because it absorbed thermal energy from the reaction mixture, causing the temperature to drop.

Interpreting Data:

Is the reaction endothermic or exothermic? Explain.


Energy in Chemical ChangesInferring:

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.



If the temperature increased instead, the reaction would be exothermic, because 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.


Links on Chemical Changes

Click the SciLinks button for links on chemical changes.

http://www.phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=scn&wcsuffix=1134


End of Section:Observing Chemical

Change


Section 2:Describing Chemical

ReactionsWhat 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 ReactionsCellular phone messages use symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.


Chemical FormulasThe 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 MatterThe 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 EquationsTo 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 EquationsBalancing Chemical Equations:

Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).


Balancing Chemical EquationsBalancing Chemical Equations:

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


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


End of Section:Describing Chemical

Reactions


Section 3:Controlling Chemical

ReactionsHow is activation energy related to chemical reactions?What factors affect the rate of a chemical reaction?


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


Energy and ReactionsBoth exothermic and endothermic reactions need energy to get started.


Rates of Chemical ReactionsThe 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 FireThree things necessary to start and maintain a fire are fuel, oxygen, and heat.


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


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


Links on Fire Safety

Click the SciLinks button for links on fire safety.

http://www.phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=scn&wcsuffix=1224


End of Section:Fire and Fire Safety


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