CHAPTER 7

Chemical reactions form new substances by

breaking and making chemical bonds.

Section 7.1students will:

• Recognize evidence of a chemical change

• Identify five types of chemical reactions

• Describe how the rate of a chemical reaction can change

chemical reactions occur everyday

• Our food digests• Metal left outside rusts• Log in the fireplace burns and

turns to ashRemember we talked about some changes are PHYSICAL while some are CHEMICAL. A physical change is simply a change in the state of matter while a chemical change involves breaking existing bonds and new bonds forming.

Give an example of a physical change. ice melting

Give an example of a chemical change. fuel cell car

A chemical reaction produces new substances by changing the way in which atoms are arranged.

Reactants–bonds broken

oxygen

(O2)(CH4)

methane+

Products–new bonds formed

carbon dioxide

(CO2) (H2O)

water+

Reactants-substances present at the beginning of a chemical reaction.

Products-substances formed by the chemical reaction.

• Chemical changes occur through chemical reactions.

• Evidence of a chemical reaction includes a color change, the formation of a precipitate, the formation of a gas, and a change in temperature.

Demos:

Burning magnesium ribbon

Iron nail in copper sulfate

Remember the baggie blast lab?

Types of chemical reactions

• Synthesis- two simple things come together to make a more complex product

• Easy way to think of synthesis• A + B → C

+gives

• Decomposition – a reactant breaks down into simpler products. One large thing breaks down into smaller parts.

• Simple way: C → A + B

Hydrogen peroxide breaks down into hydrogen gas and oxygen gas if not stored in a closed brown bottle.

2H2O2→ 2H2O + O2

In a combustion reaction, one reactant is always oxygen and another reactant often contains carbon and hydrogen.

Burning methane is a combustion reaction.

Single replacement reaction- a single element and a compound produces a new single element and a new compound.

Easy way:

A + BC → AB + C

+

→ +

An iron nail in copper sulfate produces copper and iron sulfate.

Single replacement reaction

Double replacement reaction• Simple way: • AB + CD → AC + BD• Just think of it as square dancing in PE.

Two couples dosi doeing and the teacher says switch partners. Two compounds (reactants) and when the reaction takes place the products are two new compounds.

Rates of chemical reactions can vary

• Concentration ~ a high concentration of reactants means there are a larger number of particles that can collide and react.

• What happens when you turn up the valve on a gas camp stove?

• More gas molecules to combine with oxygen and a bigger flame.

• When do you expect to most likely bump into another shopper at the mall~~

The day after Thanksgiving?Or

At 9 PM on a cold Tuesday night in mid January ?

Of course Black Friday!A greater concentration of people increases the chance you’ll bump

into another person.

Surface area~ to make a reaction go faster increasing surface helps that happen• Which would burn faster? A huge

log on my fireplace or that big log ground into saw dust and blown across the fire?

• The saw dust• Which dissolves faster a crushed

alka seltzer or a whole one?• The crushed one

The rate of a reaction may be increased by making the particles move faster. • When does the sugar dissolve in

tea better? warm or cold• Does an alka seltzer dissolve faster

in hot water or cold water?• Does a light stick glow brighter in a

cup of hot water or cold water?

Increasing temperature increases the movement of Increasing temperature increases the movement of molecules.molecules.

Adding a catalyst speeds up the rate of a chemical reaction but the catalyst remains unchanged.

•Enzymes in our bodies help reactions take place. Without them we couldn’t live. Our food would not digest. •Catalytic converters on our cars make fuel use more efficient and release less emissions.

I. Chemical reactions alter arrangements of atoms.A. Atoms interact in chemical reactions.

B. Chemical reactions can be classified.

C. The rates of chemical reactions can vary.

2. Surface Area

1. Concentration

3. Temperature

4. Catalysts

2. Chemical Changes

1. Physical Changes

3. Reactants and Products

4. Evidence of Chemical Reactions

7.17.1Section 7.1 outline

review• How are physical changes different

from chemical changes?• What are the 4 evidences of a

chemical reaction?• How can the rate of a chemical

reaction be changed?• How might chewing your food be

related to the rate of a chemical reaction?

• Name the 5 types of chemical reactions.

Chapter 7Section 2

Objectives:

•Learn why total mass does not change in a chemical reaction.

•Recognize how a chemical equation represents a chemical reaction.

•Learn how to balance chemical equations.

The law of conservation of mass states that in a chemical reaction the masses of the reactants and products are equal.

That means that in a reaction what you have in the beginning of a reaction you have all of the same stuff in the end it has often just changed phases. In other words mass is neither created or destroyed, it just changes form.

Careful observations by Lavoisier led to the discovery of the conservation of mass.

Chemical reactions can be described by chemical equations.

C + O2 → CO2Reactants direction of reaction product

Chemical equations must be balanced.

•http://www.wfu.edu/~ylwong/balanceeq/balanceq.html

Review•State the law of conversation of mass

•Is the following equation balanced? CO→C + O2

•In a chemical rexn, reactants always form?

•Splitting of water into H2 and O2 what kind of change?

•A chemical equation must be?

Chapter 7Chapter 7Sections 3 & 4Sections 3 & 4

Objectives:Objectives:Describe how energy changes in a chemical reaction.Describe how energy changes in a chemical reaction.

Explain how some chemical reactions release and some Explain how some chemical reactions release and some absorb energy.absorb energy.

Identify the relationship between the reactions of respiration Identify the relationship between the reactions of respiration and photosynthesis.and photosynthesis.

Recognize how chemistry has been used to develop Recognize how chemistry has been used to develop technology.technology.

Infer through an experiment how catalysts affect a chemical Infer through an experiment how catalysts affect a chemical reaction.reaction.

Chemical reactions Chemical reactions involve energy changes.involve energy changes.

Chemical reactions involve breaking Chemical reactions involve breaking bonds in reactants and forming new bonds in reactants and forming new bonds in the products.bonds in the products.

The energy associated with bonds is The energy associated with bonds is called called bond energybond energy. .

Energy is needed to break bonds.Energy is needed to break bonds. Energy is released when bonds are Energy is released when bonds are

formed.formed.

A reaction where energy is released is an A reaction where energy is released is an exothermic reactionexothermic reaction..

Changing from a liquid to a solid releases Changing from a liquid to a solid releases energy----this is an exothermic process.energy----this is an exothermic process.

Energy can be released as light or heat.Energy can be released as light or heat.

Other examples of Other examples of exothermic reactionsexothermic reactions

Combustion of methane is an exothermic Combustion of methane is an exothermic reaction. Example-- the house explosion reaction. Example-- the house explosion in Florence.in Florence.

A glow stick works by a chemical reaction A glow stick works by a chemical reaction that releases light.that releases light.

Lightening bugs light up due to a chem Lightening bugs light up due to a chem rxn as do some fish, squid, jellyfish, coral rxn as do some fish, squid, jellyfish, coral and shrimp.and shrimp.

A reaction where energy is absorbed is A reaction where energy is absorbed is called an called an endothermic reactionendothermic reaction..

Changing from a solid to a liquid, or Changing from a solid to a liquid, or melting, absorbs energy---this is melting, absorbs energy---this is endothermic.endothermic.

All endothermic reactions absorb energy. All endothermic reactions absorb energy. They don’t all absorb energy as heat. They don’t all absorb energy as heat. The decomposition of water by The decomposition of water by electrolysis is another example. That electrolysis is another example. That powered the hydrogen fuel cell car.powered the hydrogen fuel cell car.

Other examples of Other examples of endothermic reactionsendothermic reactions

The most important endothermic reactions on The most important endothermic reactions on Earth is photosynthesis.Earth is photosynthesis.

The reaction is:The reaction is:

6CO6CO22 + 6H + 6H22O O → C→ C66HH1212OO66 + 6O + 6O22

Photosynthesis does not absorb energy as Photosynthesis does not absorb energy as heat but as sunlight to turn carbon dioxide and heat but as sunlight to turn carbon dioxide and water into oxygen and glucose.water into oxygen and glucose.

Most oxygen comes from the ocean Most oxygen comes from the ocean (phytoplankton) rather than from the forests (phytoplankton) rather than from the forests like we all usually think. But do save a tree!like we all usually think. But do save a tree!

Life and industry depend Life and industry depend on chemical reactions.on chemical reactions.

Our bodies obtain energy from glucose (our Our bodies obtain energy from glucose (our food) through the process of food) through the process of respirationrespiration. This . This is the reverse of photosynthesis. is the reverse of photosynthesis.

PhotosynthesisPhotosynthesis6CO6CO22 + 6H + 6H22O + energy O + energy → C→ C66HH1212OO66 + 6O + 6O22

RespirationRespiration

CC66HH1212OO66 + 6O + 6O22 → → 6CO6CO22 + 6H + 6H22O + energyO + energy

Catalysts---enzymes---make this process go Catalysts---enzymes---make this process go quickly and atomatically quickly and atomatically

Uses in technology and Uses in technology and industryindustry

Catalytic converters on our cars take unwanted Catalytic converters on our cars take unwanted waste products out of the combustion of waste products out of the combustion of gasoline so it is not emitted into our air.gasoline so it is not emitted into our air.

Silicon is extracted from quarts and microchips Silicon is extracted from quarts and microchips for computer and other electronics is made.for computer and other electronics is made.

A material called photoresist is exposed to A material called photoresist is exposed to ultraviolet light producing a chemical reaction ultraviolet light producing a chemical reaction that is used in printing our newspapers and that is used in printing our newspapers and magazines.magazines.

reviewreview

Endothermic reactions always:Endothermic reactions always:Absorb energy

How are respiration and photosynthesis the opposite from each other?

The reactants of one process are the products of the other process. Respiration is exothermic; photosynthesis is endothermic.

Go to page 229 and answer questions 5-14.