Chemical

Reactions

Matter and EnergyHave you ever sat around a campfire or watched flames flicker in a

fireplace? Roasted marshmallows?

The burning of wood is a chemical reaction—a process that changes one set of chemicals into another set of chemicals.

A chemical reaction always involves changes in chemical bonds that join atoms in compounds. The elements or compounds that enter into a chemical reaction are called reactants. The elements or compounds produced by a chemical reaction are called products. As wood burns, molecules of cellulose are broken down and combine with oxygen to form carbon dioxide and water vapor, and energy is released.

Section 2-4

Interest Grabber

I.Chemical Reactions

A. process that changes or transforms one set of chemicals into another

B. always changes the chemical bonds that join atoms in compounds

C. during chemical transformations mass and energy are conserved

1. also true for chemical reactions

D. some reactions occur slowly1. example

a. combining iron and oxygen to form iron oxide (rust)

b. silver tarnishing

E. some reactions occur quickly1. example

a. a match burningb. a cake rising (from baking soda or

baking powder)

A chain rusting is a ______.

1. Chemical change only2. Physical change only3. Both a chemical &

physical change4. Neither a chemical or

physical change

A roasted a marshmallow is a ____.

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25% 25%25%25%1. Chemical change only2. Physical change only3. Both physical &

chemical changes4. Neither a physical nor

chemical change

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F. reactants1. the elements or compounds that enter into a

chemical reactionG. products

1. the elements or compounds that are produced by the chemical reaction

What are the reactants when wood burns?

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25% 25%25%25%

1. Cellulose & O2

2. CO2 & H2O3. Cellulose & H2O4. Cellulose & CO2

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What are the products when wood burns?

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25% 25%25%25%1. Cellulose & CO2

2. Water & CO2

3. Cellulose & O2

4. CO2 & O2 & H2O

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H. living organism body chemical reaction1. involves carbon dioxide

a. cells actively produce CO2 which travels through your body til you exhale it, however it is not very soluble in water

b. when CO2 enters bloodstream reacts to water and produces carbon acid

c. once it enters your lungs, it reacts again and turns into CO2 gas for you to exhale

II. Energy in reactionA. every time a bond is broken, energy is released

B. since chemical reactions involve breaking & forming bonds, they involve changes in energy

C.energy changes

1. energy can be released or absorbed

2. can occur spontaneously

3. if energy is absorbed a chemical reaction will not occur w/o a source of energy

a. Example 1 1 – hydrogen gas burning (reacting) w/ oxygen to get water

vapor 2 – energy is release in form of heat

(if gas explodes – will also produce sound & light)

b. example 21 – reverse reaction2 – changing water to hydrogen & oxygen gas3 – a great absorption of energy occurs/needed

i - need an electrical current to separate the

hydrogen and oxygen gas atoms

What type of energy is given off when wood burns?

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20% 20% 20%20%20%1. Light2. Heat3. Sound4. All of these5. None of these

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Do all organisms need chemical reactions?

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50%50%1. Yes2. No

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4.Organisms need reactions that require energy to stay alive

a. organisms must have a source of energy though

1 – plants get the energy by trapping & storing sunlight

2 - animals get the energy from eating other plants/animals

b. energy is released to grow, metabolize, break down & digest food

D. activation energy

1. not all chemical reactions that require energy happen spontaneously

a. if so flames or explosions could occur

2. activation energy

a. the energy needed to get a reaction started

b. a factor in whether the reaction is released or absorbed

Wood doesn’t burn all by itself. What must you do to start a fire? What does this mean in terms of energy?

To start a fire, you must light it with a match and kindling. You are giving the wood some

energy in the form of heat.

Once the fire gets started, it keeps burning. Why don’t you need to keep restarting the fire?

Once the fire gets going, it gives off enough heat to start more of the wood burning.

Energy Absorbing Reaction Energy Releasing Reaction

products

productsActivation energy

Activation energyreactants

reactants

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III. Enzymes A. some reactions are too slow or have activation

energies that are too high to be practicalfor tissue

1. need catalysts to make process possible

a. substance that speeds up the rate of a chemical reaction

2. works by lowering the reaction’s activation energy

B. Enzymes

1. proteins that act as biological catalysts

2. enzymes speed up chemical reactions that take place in cells

3. each enzymes handles only one specific reaction type

C. lowering the activation energy has an effect on how quickly the reaction takes

D. example 1

1. CO2 + H2O = H2CO3a. if left alone this would produce too much carbon

dioxide than can handle at once

b. your body produces an enzyme called carbonic anhydrase to help speed up the reaction by 10 million

IV. Enzyme ActionA. how does it work

1. reactants must collide w/ enough energy to existing break bonds & create new one

B. enzyme-substrate complex

1. enzymes provide a place where reactants can be brought to react together

a. site given reduces the amount of energy needed

C. Substrate

1. reactants of enzyme-catalyzed reactions

D. example1. enzyme – hexokinase

a. substrates are glucose & ATP

b. during reaction a phosphate is transferred from ATP molecule to the glucose molecule

c. the substrates then bind on the enzyme at an active site

1 – the shapes are complementary so they fit like a lock & key

2 – the enzyme & substrate the bind by intermolecular forces & form an enzyme-substrate complex

d. this complex stays bounded until the reaction is done then the 2 are released so the process can happen again

*** see video

E. regulation of enzyme activity

1. variables, like in experiments, can affect a chemical reaction

a. temperature, pH levels …

2. enzymes work best at certain pH values

3. temperature – best at 37 degrees C – normal body temperature

a. when ill enzymes not properly functioning

4. cells regulate the activities of enzymes in many ways

a. proteins in cells turn on/off the enzymes at critical stages in the cell’s life

1 – help regulate chemical pathways

2 – make materials cells need

3- release energy

4 – transfer info

What is the relationship between enzyme concentration & reaction rate

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25% 25%25%25%1. The reaction rate decreases w/ increasing enzyme concentration.

2. The reaction rate increases w/ decreasing enzyme concentration.

3. Reaction rate increases with increasing enzyme concentration.

4. The variables are not directly rated.

An enzyme speeds up a reaction by

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25% 25%25%25%1. lowering the activation energy.

2. raising the activation energy.

3. releasing energy.4. absorbing energy.

In a chemical reaction, a reactant bind to an enzyme at a region known as the

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20% 20% 20%20%20%1. catalyst.2. product.3. substrate.4. active site.5. reactive site.