Energy Changes in Chemical Reactions

1
Thermochemistry

• Energy Changes in Chemical Reactions
• Chemistry 12

2
Thermodynamics

• The study of energy and its interconversions.

3
Types of Energy

• Energy the capacity to do work
• Types
• Radiant energy
• Thermal energy
• Chemical energy
• Potential energy
• Law of Conservation of Energy

Energy can be converted from one form to another.
4
Kinetic vs Potential Energy

• Kinetic Energy energy that an object possesses
  by being in motion.
• Potential Energy energy that an object
  possesses as a result of its composition or its
  position with respect to another object

5
Energy Changes in Chemical Reactions

• Almost all chemical reactions absorb or produce
  (release) energy.
• Heat is the transfer of thermal energy between
  two bodies that are at different temperatures.
  (sometimes referred to as heat flow)
• Temperature is the average kinetic energy of the
  molecules.
• Law of Conservation of Energy states that energy
  may neither be created nor destroyed

6

• The system is the specific part of the universe
  that we are studying. The surroundings are the
  rest of the universe outside the system.
• system surroundings universe
• ?E Ef Ei
• ?Esys ?Esurr 0
• Or ?Esys -?Esurr

7
Examples of Systems
Open
Isolated
Closed
Water vapor
heat
heat
8

• A reaction is exothermic if it gives off heat
• energy flows from the system to the surroundings
  
• (q is negative)
• A reaction is endothermic if it absorbs/takes in
  heat
• energy flows from the surroundings into the
  system
• (q is positive)

9
More on Energy

• Total change in energy (?E)
• aka. First Law of Thermodynamics
• ?E q w (heat work)
• q heat absorbed by/lost from the system
• w work done on/by a system on its surroundings