Section 2.4

Chemical Reactions

• Chemical reactions change substances into different substances by breaking and forming bonds.

• Chemical reactions are responsible for all the actions of organisms. – Examples

• Photosynthesis• Respiration (breathing)• Digestion

• Metabolism is all the chemical reactions in an organism

• Oxygen+Sugars CO2 + Water (Reactants) (Products)

• Reactants are changed in a reaction

• EXAMPLE:

• Products are formed in a reaction

Activation Energy: energy required to start a reaction.

Exothermic• Energy EXITS!• The prefix “exo-”

means “out”• Example:

– respiration

• Energy goes IN!• The prefix “Endo”

means “into”• Example:

- photosynthesis

Endothermic

Two Types of Reactions

Vocabulary Check

1. Making and breaking chemical bonds are examples of ____________.

2. Bonds are broken in the ______, which are the chemicals that are changed during the process.

3. Bonds are made in the ________, which are the chemicals that result from the process.

Vocabulary Check cont…

1. The ________ is the amount of energy needed to start a reaction.

2. If a reaction absorbs more energy than it releases, it is called an __________ reaction.

3. If a reaction releases more energy than it absorbs, it is called an __________ reaction.

Endo or Exo?

1.

Which is the solute, which is the solvent?

2.

Reactants and Products?

3. 2H2O2 2H2O + O2

• 4. How are exothermic and endothermic reactions different?

• Exothermic or endothermic?

Exothermic or endothermic?

Exothermic or Endothermic?