Energy Changes in Reactions

Lab 7.1  Introduction to Endothermic/Exothermic Processes

Remember worksheet.  In this unit we will apply many of the ideas (models) already developed in the course. 

Remember from Unit One.  Energy is the ability to do work.  When energy is transferred from one object to another work is done - a force is exerted over a distance.  This changes either the motion (KE) or position (PE) of the object.   The object may gain kinetic energy (energy of motion) if it moves faster.  The marbles rolling collided with the golf tee at the bottom of the ramp.   The moving marble transferred kinetic energyint eh collision and made the golf tee move.  The marble did work on the tee.  Or the object may gain potential energy (stored energy) if the position is changed (example the object gets hgiher off the ground or the spring is stretched).  A person does work pulling the spring to its stretched position and the spring gains potential energy.

Remember from Unit Five and Six.  In a chemical reaction, the particles are rearranged.  The position of the particles are changed when bonds are broken and new bonds are formed.  When water molecules collide with a sugar cube and break the attractions between the sugar molecules and new attractions form between the sugar molecules and water molecules.  When water molecules collide with ionc solids, the ionic bonds between the ions are broken and new attrctions form between the ions and water molecules. 

Remember from Unit Two.  We have already used our model of energy to desribe particles in motion. Moving particles have kinetic energy.  We measured that kinetic energy with a thermomoter.  Temperature is a measure of the average knetic energy of the particles.  We described the energy transferred as heat when particles collide and transfer their kinetic energy to make other particles move faster increasing their temperature (average kinetic energy).

In this unit, the energy transfers involved at the partcile level are investigated.  Particles collide (just like marbles and golf tees).  Particles are attracted to each other (just like the spring).  Particles must have potential energy due to their positions and the attractions  between them.