chemical reactions observing chemical change describing chemical reactions controlling chemical...
TRANSCRIPT
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
Energy in Chemical Changes
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
Chemical Reactions
Energy in Chemical Changes
20ºC
Calculating:
How many degrees did the temperature drop between2 minutes and 5 minutes?
- Observing Chemical Change
Chemical Reactions
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
Chemical Reactions
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
Chemical Reactions
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
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
- Observing Chemical Change
Chemical Reactions
Links on Chemical Changes
Click the SciLinks button for links on chemical changes.
- Observing Chemical Change
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.
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 (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.
- Describing Chemical Reactions
Chemical Reactions
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).
- Describing Chemical Reactions
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
Chemical Reactions - Describing Chemical Reactions
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.
- Describing Chemical Reactions
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.
Chemical Reactions - Controlling Chemical Reactions
Energy and Reactions
Both exothermic and endothermic reactions need energy to get started.
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 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.
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
Chemical Reactions - 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.
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