Chemical Reactions

And Enzymes

A chemical reaction is a process that changes, or transforms, one set of

chemicals into another.

• Mass and energy are conserved

• Reactants become products

• Always involve changes in the chemical bonds that join the atoms of the compounds

Because atoms are neither created nor destroyed in a reaction, a chemical

equation must have an equal number of atoms of each element on each side of the arrow (i.e. the equation is said to be 'balanced').

                                                                                                         

   

Steps involved in writing a 'balanced' equation for a chemical reaction:

1. Experimentally determine reactants and products 2. Write 'un-balanced' equation using formulas of reactants and products 3. Write 'balanced' equation by determining coefficients that provide equal numbers of each type of atom on each side of the equation (generally, whole number values)

Note! Subscripts should never be changed when trying to balance a

chemical equation. Changing a subscript changes the actual identity of a product or reactant. Balancing a

chemical equation only involves changing the relative amounts of

each product or reactant.

__CO2 +__H2O C6H12O6 + __O2

6CO2 +__H2O C6H12O6 + __O2

6 carbons in glucose on the right means you need 6 on the left so place the coefficient 6 in front of

the carbon dioxide

6CO2 + 6H2O C6H12O6 + __O2

12 hydrogen in the glucose on the right means you must have 12 on

the left. Since the hydrogen in water occurs in pairs, you will

need 6 pairs to equal 12.

6CO2 + 6H2O C6H12O6 + 6O2

There are 18 oxygen atoms in the reactants on the left (12 in carbon

dioxide and 6 in water) so you need 18 on the right. There are already 6

present in the glucose so you will need 6 pair (12) of the oxygen

6CO2 + 6H2O C6H12O6 + 6O2

This is a balanced equation!

Try this one:

Is this your result?

Energy

• Exothermic reactions (release energy) occur spontaneously and give off heat, light, and/or sound energy

• Endothermic reactions (absorb energy) need a source of energy and store it in the bonds

• Organisms get energy from nutrients

Activation Energy

• energy that must be added to get a reaction started, which is recovered as the reaction proceeds

• difference in energy between reactants and products

• energy that is lost as heat • free energy • equal to the entropy times the absolute

temperature

Graphing it……

Enzymes

• Catalyst (controls rate of reaction) that lowers activation energy

• Specialized protein molecules

• Useful in organisms

See what enzymes do…..?

Enzymes provide a place where reactants can be brought together, reducing the energy needs for the reaction. Watch the substrates come into the

active site of the enzyme model below:

Enzymes must be regulated by the cell to make them able to adjust to changes in the

environment

Explanation?