Chemical

Reactions

I. CHEMICAL Reactions:

• All the chemical reactions in our bodies are called metabolism.

•Breakdown and reassemble molecules in the body.

• Chemical bonds are broken and formed during chemical reactions.

II. Writing a Chemical Equation:

CH4 + 2O2 CO2 + 2H2O

REACTANTS PRODUCTSYIELDS

(methane) + (oxygen) (carbon dioxide) + (water)

II. Writing a Chemical Equation:

• Coefficients = # of molecules of a compound

Ex: 6O2 = 6 molecules of Oxygen (O)

3H2O = 3 molecules of H2O

CH4 + 2O2 CO2 + 2H2O

II. Writing a Chemical Equation:

• Subscripts = # of atoms of an element

Ex: CH4 = 1 atom C, 4 atoms H

CO2 = 1 atom of C, 2 atoms O

CH4 + 2O2 CO2 + 2H2O

II. Writing a Chemical Equation:

• How many atoms of O are in 6O2 ?

12 atoms of O!

III. Balancing Chemical Equations:• In ALL chemical equations the same

number of atoms of elements are on the reactant and the product side of chemical equations oWhy?

Because of the Law of Conservation of Matter (atoms are never created or destroyed; they are simply rearranged!)

III. Balancing Chemical Equations:oWe balance equations so the Law

of Conservation of Mater is NOT violated!

oWe must always balance

equations using coefficients!!

Tips for balancing equations:oSubscripts can never be

changed!

oCoefficients must always be placed in FRONT of the entire compound!

oCreate an atom inventory

Ex: Balance the following equations so the Law of Conservation of Matter is NOT violated:

H2 + O2 H2O

Ex: Balance the following equations so the Law of Conservation of Matter is NOT violated:

CaO + KBr K2O + CaBr2

Ex: Balance the following equations so the Law of Conservation of Matter is NOT violated:

Al2S3 + BaCl2 AlCl3 + BaS

Energy of Reactions

IV. Energy of Reactions• The key to a

chemical reaction is energy!

• Most compounds in living things cannot undergo chemical reactions without energy

IV. Energy of Reactions• Activation energy =

the minimum amount of energy needed for reactants to form products in a chemical reactionoLook at Graph A: the

peak in the graph represents the amount of energy that must be added to the system to make the reaction occur!

Graph A

IV. Energy of Reactions• All living things are chemical factories

driven by chemical reactions!• Enzymes (catalysts) need to be present in

order to reduce the activation energy and allow the reaction to proceed quickly.

IV. Energy of Reactions• Look at Graph B: the enzyme

lowers the activation energy and the product will be formed sooner!Graph B

IV. Energy of Reactions• Catalyst = a substance that

lowers the activation energy needed to start a chemical reaction.

• Enzyme = special proteins that are biological catalysts that speed up the rate of a chemical reaction

Essential to life!Specific to one reaction

How do ENZYMES Work?• The reactants that bind to the

enzyme are called substrates.• The specific location where a

substrate binds on an enzyme is called the active site.

How do ENZYMES Work?

• The active site and substrate have complementary shapes (lock-and-key).oEnzymes are very specific for the substrates that will change!

How do ENZYMES Work?• When the enzyme-substrate

complex forms, chemical bonds are broken and new bonds form to produce the products.

• Enzyme releases the product and the enzyme can be used again

Factors That Affect Enzymes:1) pH (how acidic or basic a

substance is)2) Temperature

• most enzymes in human cells are most active at 98.6F

• pH & temperature will denature (change the shape) of the enzyme so it will not be able to bond with the corresponding substrate!

Examples Of Enzymes Working:• Helps with digestion• DNA replication• Enzymes in the venom of a

venomous snake break down the membranes of a person’s red blood cells

Examples Of Enzymes Working:

• Hard green apples ripen because of the action of enzymes

• Photosynthesis and cellular respiration provide energy for the cell with the help of enzymes

pH, Acids, Bases

V. pH, Acid, BASES:

• pH = how acidic or basic a substance is

• Acid = substance that forms H+ (hydrogen ions) in water

HCl H+ + Cl- (pH LESS than 7)

Water

V. pH, Acid, BASES:

• Base = substance that forms OH- (hydroxide ions) in water

NaOH Na+ + OH-

(pH MORE than 7) 

Water

The pH scale:

0 7 14

BASEACID

NEUTRAL