spacer
Unit #1Unit #2Unit #3Unit #4Unit #5Unit #6Unit #7Unit #8Unit #9Unit #10
spacerUNIT # 2  
spacerspacerIntroduction
spacerspacerObjectives
spacerspacerReading


spacer2.1 Physical
spacerStates of
spacerMatter

spacer2.2 Physical &
spacerChemical
spacerProperties
spacer2.3 Physical &
spacerChemical
spacerChanges

spacer2.4 Classific-
spaceration of

spacerMatter
spacerPure Substances

spacerMixtures

spacer2.5 Energy
spacerPotential and Kinetic Energy

spacerEndothermic and Exothermic Reactions
spacerLaw of Conservation of Energy

spacerspacerProblems
   

Unit #2 MATTER AND ENERGY

2.5 - Energy

2.5.2 - Endothermic and Exothermic Reactions

When physical or chemical changes (section 2.3) occur, energy is either produced or absorbed. When the process produces energy, it is an exothermic process. When the process absorbs energy, it is an endothermic process.

The melting of snow is an endothermic process. Let's analyze this process. A source of heat causes the phase transition from solid to liquid. In section 2.1 we analyzed the submicroscopic properties between solids, liquids and gases.

melting of snow

The heat energy from the sun causes snow to melt. In the solid form, snow has regular hexagonal shapes. The hexagonal units touch, and are tightly packed in a regular arrangement.

a snowflake has hexagonal shapes

The snow absorbs the heat energy of the sun. In the melting process, the sun's heat energy is converted to the liquid water's kinetic energy. As the snow melts, the water molecules increase in kinetic energy resulting in losing their regular hexagonal shapes, and becoming mobile so that the water molecules in the liquid state can glide over each other. In the end, when snow melts to become a puddle of water, an endothermic process has occurred.


Section 3.5
Energy ..p62

Back



All contents copyrighted © 1996-2006
British Columbia Institute of Technology
Chemistry Department - 3700 Willingdon Avenue
Burnaby, B.C. Canada V5G 3H2