Unit 7: Energy

Objective Understand the law of conservation of energy in terms of gaining and losing energy.

Law of Conservation of Energy Energy is neither created nor destroyed.

Energy Potential Energy: energy of position; stored energy Kinetic Energy: energy related to motion

Example: a toy “wind-up” car When you wind up the car and tighten the spring, you supply the car with potential energy. As the car moves, the spring unwinds, and provides kinetic energy to the moving parts. In this example, potential energy has been converted to kinetic energy.

Example: a snowboarder poised at the top of a hill At the top of the hill, the snowboarder has potential energy (energy of position). As the snowboarder races down the hill, the stored potential energy is converted to kinetic energy.

Where is the potential energy the highest? Where is the kinetic energy the highest?

Which type of energy is the greatest in each picture?

How does this apply to Chemical Energy? • Energy stored within chemical bonds is stored chemical energy (a form of potential energy).

Chemical Energy When a fuel is burned, these chemical bonds break and the reactant atoms reorganize to form new bonds. The products formed have more stable atom arrangements. Some of the energy stored in the reactants is released in the form of heat and light.

Example: the burning of methane gas (CH4) – the gas we use in our laboratory burners!

Example: Methane, CH4 CH4 + 2O2  CO2 + 2H2O + ENERGY

Chemical reactions or changes may be: endothermic or exothermic

Endothermic Change: an energy- requiring process; absorbs energy Gets warmer!

Exothermic Change: an energy- releasing process; gives off energy Gets cooler!

Endothermic or Exothermic? Compare the input of energy to break the bonds (start the reaction) to the output of energy when new bonds are formed IF… more energy is given off than was added, the process is exothermic. more energy is added than is given off, the process is endothermic.

Graph of Exothermic Reaction: REACTANTS PRODUCTS

Graph of Endothermic Reaction: PRODUCTS REACTANTS