Changes in Matter and Energy
• Matter cannot be created or destroyed.
• But it can be changed and when it does, that is how
we get energy!
• Energy - capacity to do work or produce heat
– Energy is always involved in physical and
chemical changes.
– Energy can take several forms: Heat, light, (sound,
chemical, electrical)
– Measured in calories, Calories (kcal), and joules
• Law of Conservation of Energy: Energy
cannot be created or destroyed.
• Energy can be transferred.
Kinetic and Potential Energy
Kinetic energy: is the energy of motion.
Potential Energy: energy of position; stored energy
CHEMICAL BONDS!!!
• Total Energy = KE + PE
• Temperature: kinetic energy of all particles
within matter.
• Total Energy for a “system” doesn’t change
Endothermic
– energy is absorbed
– Substance gets cold
– Loss of KE, gain of PE
– Ex: Class demo
Exothermic
– energy is released
– Substance gets hot
– Gain of KE, loss of PE, more KE
– Ex: gummy bear sacrifice
Exothermic or Endothermic?
•
•
•
•
Releases energy
Temperature rises
Gets colder
Needs energy to be added for the reaction to
occur
• Chemicals have less potential energy after the
reaction
• Chemicals have more potential energy after
the reaction
Create a Venn Diagram for Exothermic
and Endothermic Reactions
Energy
Specific Heat (s) : amount of energy (heat) required to
change the temperature of one gram of a substance by
1 oC
 Varies from one substance to another
Calorie (cal): the amount of energy required to raise the
temperature of one gram of water by one Celcius
degree
 Standard unit for energy is the joule (J)
 1 cal = 4.184 J
• Water has a specific heat = 1 cal/goC or 4.184 J/goC
– Water has the second highest specific heat capacity
of all known substances. So it requires high
amounts of heat energy to raise water temperature.
– water also has a high energy/heat requirement for
evaporation
• SIRON = 0.449 J/goC
– Which would heat up faster, 5.00 grams of iron or
5.00 grams of water?
– Which would cool down faster, 5.00 grams of iron
or 5.00 grams of water?
– Which is a better thermal conductor?
– Which is a better insulator?
Q = s x m x DT
Q = energy (heat) required (J) or (cal)
s = specific heat capacity (J/goC) or (cal/goC)
m = mass of the sample in grams
DT = change in temperature in oC
 A 2.8 g sample of a pure metal requires 10.1 J of
energy to change its temperature from 21 oC to 36 oC.
What is the specific heat of the metal?
s= Q
=
10.1 J
= 0.24 J/goC
m x DT
(2.8 g x 15oC)
Example 2
• Calculate the heat capacity of a piece of wood if
1500.0 g of the wood absorbs 67,500 joules of heat,
and its temperature changes from 32°C to 57°C.