Chemical Reactions Observing Chemical Change Describing Chemical Reactions Controlling Chemical...

Chemical Reactions

Observing Chemical Change

Describing Chemical Reactions

Controlling Chemical Reactions

Fire and Fire Safety

Table of Contents

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

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.

- Observing Chemical Change

Chemical Reactions


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?


Chemical Reactions


20ºC

Calculating:

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


Chemical Reactions


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.


Chemical Reactions


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?


Chemical Reactions


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.


Chemical Reactions

Asking QuestionsBefore 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.

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.

Question Answer

Properties and Changes of Matter


Chemical Reactions

Links on Chemical Changes

Click the SciLinks button for links on chemical changes.


Chemical Reactions

End of Section:Observing Chemical Change

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.


What Are Chemical Equations?

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


Chemical Formulas

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


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.


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


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.


Chemical Reactions


Balancing Chemical Equations:

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


Chemical Reactions


Balancing 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.

Chemical Reactions

Building VocabularyUsing 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.

reactant A substance you have at the beginning of a reaction is a reactant.

product A new substance produced in a reaction is a product.

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.

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

End of Section:Describing Chemical Reactions

Chemical Reactions - Controlling Chemical Reactions

Energy and Reactions

All chemical reactions need 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. At the end of a reaction, an enzyme molecule is unchanged.

Chemical Reactions

Relating Cause and EffectAs 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

Data Sharing Lab

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

Chemical Reactions

Exothermic and Endothermic Reactions

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

- Controlling Chemical Reactions

Chemical Reactions

End of Section: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.


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


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.

Chemical Reactions

What You Know

What You Learned

Using Prior KnowledgeBefore you read, write what you know about fire safety in a graphic organizer like the one below. As you read, write what you learn.

1. A fire needs fuel to burn.2. A fire need oxygen to burn.3. All homes should have smoke detectors.

1. Fire is a result of a combustion reaction.2. The most deadly fires start with cigarettes.3. Baking soda can be used to put out small fires.

- Fire and Fire Safety

Chemical Reactions

Links on Fire Safety

Click the SciLinks button for links on fire safety.

- Fire and Fire Safety

Chemical Reactions

End of Section:Fire and Fire

Safety

Chemical Reactions

Graphic Organizer

Endothermic reactions

Chemical reactions

Exothermic reactions Equations

Activation energy Chemical

symbolsArrows and plus signs

Coefficients

can be are written as

which require written using

balanced with

Chemical Reactions

End of Section:Graphic Organizer

Chemical Reactions Observing Chemical Change Describing Chemical Reactions Controlling Chemical...

Documents

Transcript of Chemical Reactions Observing Chemical Change Describing Chemical Reactions Controlling Chemical...