Energy and Reactions

Honors Biology

Energy• Energy – ability to do work or cause a change– Kinetic Energy energy of motion

• Ex: Heat, moving ball– Potential Energy stored energy as a result of

position or location• Ex: Sitting ball

• ATP – adenosine triphosphate– Unit of energy cells use– 3 phosphates; 3rd P has high energy bond

ATP

Triphosphate

Ribose

Adenine

Chemical Reactions• Bonds between atoms are made or broken and

the substances change into something else• Represented by chemical equations• Ex: Methane burning in air

CH4 + 2O2 → CO2 + 2H2O(reactants) (products)

• Equation must be balanced (coefficient vs. subscript)… PRACTICE!!!– Atoms are never created or destroyed, only change

form

PRACTICE PROBLEMS

1) ____ H2 + ____ O2 ____ H2O

2) __ AlBr3 + __ Cl2 __ AlCl3 + Br2

**3) __Ca(OH)2 + __H3PO4 __ Ca3(PO4)2 + __H2O

Answers

WRONG: 4AlBr3 + 6 Cl2 4 AlCl3 + 6 Br2

2 AlBr3 + 3 Cl2 2 AlCl3 + 3 Br2

Answers

1) 2 H2 + 1 O2 2 H2O

2) 2 AlBr3 + 3 Cl2 2 AlCl3 + 3 Br2

**3) 3 Ca(OH)2 + 2 H3PO4 1 Ca3(PO4)2 + 6 H2O

• Endergonic Reactions – absorbs energy– Energy absorbed from surroundings and stored in

bonds– Ex: Photosynthesis– Products have more ENERGY than reactants

• Exergonic Reactions – releases energy– Releases ENERGY to environment– Ex: Cellular Respiration– Reactants have more ENERGY than products

• Energy Coupling – Energy released from exergonic rxns powers endergonic ones

Real Life Examples…

• Exergonic (Exothermic)– Cellular Respiration– Energy (ATP) is released when glucose is

broken down• Endergonic (Endothermic) – Photosynthesis– Energy (ATP) is NEEDED (consumed) to put

together glucose from CO2, H20 and sunlight