Chemistry 12 Unit 1
THERMOCHEMISTRY
Energy: the capacity to move matter
Units: Joule (J), calorie (cal)
Kinetic Energy
(KE)
The energy of motion
Potential Energy
(PE)
Energy that is stored
Thermal energy: due to kinetic energy (motion) of atoms/molecules
Temperature (t): measures average kinetic energy of particles on a
relative scale.
Units: Celsius (◦C), Kelvin (K)
(Absolute zero = 0K or -273 ◦C – no particle motion)
Heat: a transfer of kinetic energy from a higher
temperature system to a lower temperature system
Thermochemistry is a study of the heat that is lost or
gained during chemical reactions
Exothermic changes:
heat is given off by the system
Endothermic changes:
heat is taken in by the system
surroundings
system
System
Effect on
surroundings
Heat value of
system
Endothermic
Takes in heat
Cools
+
Exothermic
Gives off heat
Warms
-
SPECIFIC HEAT CAPACITY (C)
PREDICT/OBSERVE/EXPLAIN
Specific heat capacity is the amount of heat needed to raise the
temperature of one gram of a substance one degree Celsius.
Basically, it is the ability of a substance to store heat energy.
Different substances have different specific heat capacities. Water
has a relatively high specific heat capacity, meaning that is takes a
lot of heat to raise the temperature of water, while metals tend to
have a low heat capacity.
In this experiment, the specific heat capacities of five different
metals were compared. Equal weights of the metals were heated
until all reached the same temperature. Each metal was then
placed on a block of paraffin wax and allowed to cool. During
cooling, heat energy is transferred from the metal to the block of
wax, melting the wax and imbedding the metals into the block.
1. Which metal do you predict
will melt the most wax and
why?
2. Which metal do you predict will
melt the least wax and why?
3. List the metals in order of depth
in the wax.
(from most deep to least deep)
4. How does the specific heat
capacity of a metal relate to
the amount of wax it will melt
while cooling?
5. Daryl and Cheri each designed a frying pan. They had to choose which
metal to use. Daryl wanted his pan to reach a high temperature with the least
amount of heat applied. Cheri wanted her pan to stay at a high temperature
even when the heat was turned low. Which metal listed in the table would be
best for Daryl, and which metal would be best for Cheri? Give reasons for
your answers.
∆t = tfinal - tinitial
So, using this formula we can solve for any of the four variables.
Rearrange the formula to solve for:
Mass (m)
Specific heat
capacity (c)
Temperature
change (∆t)
Example 1:
60.0 g of water at 26.5C is cooled to 9.70C. How much
heat was lost by the water?
Example 2:
60.0 g of canola oil lost 4.0 x 103 J of energy, resulting in a
temperature decrease from 35.0C to 5.2C. Calculate the
specific heat capacity of the canola oil.
Homework:
1.Heat calculations worksheet
2.Course expectations contract signed
3.Lab Safety contract signed