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KEY CONCEPT Life depends on chemical reactions.

The ability to do work or cause change Occurs in various forms Energy and Matter Energy The ability to do work or cause change Occurs in various forms Can be converted to another form Forms important to biological systems are chemical, thermal, electrical and mechanical energy Free energy is the energy in a system that is available for work

States of Matter Atoms are in constant motion The rate at which atoms or molecules in a substance move determines its state

Solid Molecules tightly linked together in a definite shape Vibrate in place Fixed volume and shape

Liquids Molecules not as tightly linked as a solid Maintain fixed volume Able to flow and conform to shape of container

Molecules have little or no attraction to each other Gas Molecules have little or no attraction to each other Fill the volume of the occupied container Move most rapidly To cause a substance to change state, thermal energy (heat) must be added to or removed from a substance

Living things undergo thousands of chemical reactions as part of the life process

Many are very complex involving multistep sequences called biochemical pathways Chemical equations represent chemical reactions Reactants are shown on the left side of the equation Products are shown on the right side

The number of each kind of atom must be the same on either side of the arrow (equation must be balanced) Bonds may be broken or made forming new compounds C6H12O6 + 6O2 6CO2 + 6H2O

Bonds break and form during chemical reactions. Chemical reactions change substances into different ones by breaking and forming chemical bonds. Reactants are changed during a chemical reaction. Products are made by a chemical reaction. C6H12O6 + 6O2 6CO2 + 6H2O Products Reactants

Bond energy is the amount of energy that breaks a bond. Energy is added to break bonds. Energy is released when bonds form. A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3

1. How is bond formation represented by the snapping sound? 2. How is bond energy related to your separation of magnets?

Chemical reactions release or absorb energy. Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction.

Exothermic (also exergonic) reactions release more energy than they absorb (e.g. cellular respiration). Reactants have higher bond energies than products. Excess energy is released by the reaction.

Endothermic reactions (also endergonic) absorb more energy than they release (e.g. photosynthesis). Reactants have lower bond energies than products. Energy is absorbed by the reaction to make up the difference.

Oxidation reaction – reactant loses electron(s) becoming more positive Reduction-Oxidation Reactions Many of the chemical reactions that help transfer energy in living organisms involve the transfer of electrons (reduction-oxidation = redox reactions) Oxidation reaction – reactant loses electron(s) becoming more positive Reduction reaction – reactant gains electron(s) becoming more negative