- Velocity. A specific level of energy is required for a bond to occur. This energy
level is called activation energyand is different for each chemical reaction. - Orientation. Two atoms, ions, or molecules must strike each other at a
position where bonding can occur. - Reaction rate. Collisions must occur frequently at the proper orientation
and at the activation rate in order for bonding to happen. There are two
ways to increase the reaction rate. These are an increase in temperature and
an increase in pressure. Both cause atoms, ions, and molecules to move
faster and increase the probability of a collision. - Size. The atomic weight of an element influences the speed of a chemical
reaction. An atom with a larger atomic weight than another atom requires
more energy to be expended to increase the speed of the chemical reaction
that binds the atom to another atom.
CATALYST: MAKING THINGS HAPPEN
Living organisms possess large molecules of proteins that are called enzymes.
These enzymes act as catalysts. A catalysts is a chemical substance that speeds-
up the rate of a chemical reaction. These catalysts do this without affecting the
end products of the reaction, nor permanently altering themselves.
In order for an enzyme to be effective it must interact with a chemical called
a substrate.The enzyme attaches itself to the substrate in an area that will most
likely increase its ability to react. This enzyme-substrate complexlowers the
activation energy of the reaction and enables the collision of chemicals involved
in the reaction to be more effective.
An important factor of enzymes is that they can reduce the reaction time with-
out the need to increase temperature. This is very important in living organisms
because high temperatures can break apart the proteins that make up the cell.
CHEMICAL COMPOUND:
MAKING SOMETHING USEFUL
As you learned previously in this chapter, a chemical element is a substance that
cannot be divided into other chemical substances. For example, you cannot fur-
ther divide hydrogen into anything because hydrogen is an element.
CHAPTER 2 Chemical Elements of Microorganisms^35