Chapter 6 Chemical Reactions Table of Contents Chapter Preview 6.1 Observing Chemical Change 6.2...

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, it

a. 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 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.

What happens during a chemical reaction?


Section 1: Observing Chemical Change

Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties.

Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.


Matter and ChangeHow can changes in matter be described?

Physical Property

Chemical Property

Changes in matter can be described in terms of physical changes and chemical changes

A characteristic of a substance that can be observed with out changing into another substance.

A characteristic of a substance that describes its ability to change into other substances.


Matter and ChangePhysical Change Any change that alters the form or

appearance of a substance but does not make the substance into another substance.


Matter and ChangeChemical Property A characteristic of a substance

that describes its ability to change into other substances.


Properties and Changes in Matter

Chemical changes occur when bonds break and new bonds form.


Evidence for Chemical ReactionsHow can you tell when a chemical reaction occurs?

Precipitate

Endothermic Reaction

Exothermic Reaction

Chemical reactions involve changes in properties and changes in energy that you can observe.

A solid that forms from solution during a chemical reaction.

The making and breaking of bonds results in a net absorption of energy

The making and breaking of bonds results in a net release of energy.


Evidence for Chemical Reactions

How can you tell when a chemical reaction occurs?

4 Observations of Chemical Change

1. There is a formation of gas which can be seen by a fizzing or bubbling.

2. The reaction will cause heat, light, or odor to be emitted

3. A color change is produced.

4. A solid is formed during the change.


Section 1 Quick QuizWhat happens when chemical bonds break and new bonds form?

A.A physical change

B.A chemical reaction

C.Matter is destroyed

D.Surface area increases

Answer: B – A chemical reaction


Section 1 Quick QuizA chemical reaction that absorbs energy in the form of heat is described as

A.endothermic

B.exothermic

C.combustion

D.unbalanced

Answer: A - endothermic


Section 1 Quick QuizEvery chemical reaction involves a change in

A.mass

B.energy

C.concentration

D.state

Answer: B - energy


Section 1 Quick QuizOne example of a chemical change is

A.filtering

B.burning wood

C.boiling water

D.crushing a can

Answer: B – burning wood


Section 1 Quick QuizAnything that has mass and takes up space is considered

A.matter

B.energy

C.chemistry

D.endothermic

Answer: A - matter


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?



About 20ºC

Calculating:

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



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.



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?



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.


Section 2: Describing Chemical Reactions

Standard 8.5.b: Students know the idea of atoms explains the conservation of matter. In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.


What Are Chemical Equations?What information does a chemical equation contain?

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 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).



http://education.jlab.org/elementbalancing/index.html


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


Section 2 Quick QuizCaCO represents a chemicalA.symbol.B.subscript.C.formula.D.reaction.

Answer: C - formula


Section 2 Quick QuizA chemical equation that shows the same number of each kind of atom on both sides of the equation is said to beA.balanced.B.unbalanced.C.an incomplete reaction.D.a replacement reaction.

Answer: A - balanced


Section 2 Quick QuizA bottle of hydrogen peroxide that eventually turns into a bottle of water and oxygen gas is an example of aA.replacement reaction.B.precipitate reaction.C.decomposition reaction.D.synthesis reaction.

Answer: C - decomposition


Section 2 Quick QuizThe substances listed on the left side of a chemical equation are theA.coefficients.B.products.C.reactants.D.precipitates.

Answer: C - reactants


Section 2 Quick QuizIn a chemical equation, numbers often appear in front of a chemical formula. These numbers tell you theA.number of molecules in each atom in the reaction.B.number of molecules or atoms of each substance in the reaction.C.number of elements in the reaction.D.number of atoms in each molecule in the reaction.

Answer: B – number of molecules or atoms of each substance in the reaction


Section 3: Controlling Chemical Reactions

Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties.



Energy and ReactionsHow is activation energy related to chemical reactions?

Activation Energy

Potential Energy

Kinetic Energy

All chemical reactions require a certain amount of activation energy to get started.

The minimum amount of energy needed to start a chemical reaction.

Stored energy that results from the position or shape of an object.

Energy that an object has due to its motion.


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


Energy and ReactionsExothermic Reaction

Endothermic Reaction

A reaction that releases energy in the form of heat.

A reaction that absorbs energy in the form of heat.


Energy and Reactions

Both exothermic and endothermic reactions need energy to get started.


Rates of Chemical ReactionsWhat factors affect the rate of a chemical reaction?

Catalyst

Inhibitor

Enzyme

Factors that affect rates of reaction include: surface area; temperature; concentration; and the presence of catalysts and inhibitors.

A material that increases the rate of reaction by lowering the activation energy.

A material used to decrease the rate of reaction.

Biological catalysts found in the

cells of the body.


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.


Section 3 Quick QuizThe minimum amount of energy that has to be added to start a reaction is theA.exothermic energy.B.endothermic energy.C.activation energy.D.chemical energy.

Answer: C – activation energy


Section 3 Quick QuizChemicals that act as biological catalysts by speeding up reactions in living things areA.enzymes.B.inhibitors.C.reactants.D.fuels.

Answer: A - enzymes


Section 3 Quick QuizA material used to decrease the rate of a chemical reaction is a(n)A.catalyst.B.enzyme.C.fuel.D.inhibitor.

Answer: D - inhibitor


Section 4: Fire and Fire Safety



Understanding FireWhat are the three things necessary to maintain a fire?

• Three things necessary to start and maintain a fire are:

• fuel • oxygen • 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 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.

The best form of fire safety is prevention.


Section 3 Quick QuizIn what way can a fire be brought under control?

A.Add fuel.B.Add oxygen.C.Remove oxygen.D.Remove carbon dioxide.

Answer: C – Remove oxygen


Section 3 Quick QuizWhat is the best form of fire safety?

A.a water hoseB.an extinguisherC.the fire departmentD.fire prevention

Answer: D – fire prevention


Section 3 Quick QuizThe best way to put out a small kitchen fire is to

A.blow it outB.use a garden hoseC.turn off the appliancesD.cover it or use a home fire extinguisher

Answer: D – cover it or use a home fire extinguisher

Chapter 6 Chemical Reactions Table of Contents Chapter Preview 6.1 Observing Chemical Change 6.2...

Documents

Transcript of Chapter 6 Chemical Reactions Table of Contents Chapter Preview 6.1 Observing Chemical Change 6.2...