6-3: Cooking Fuels
Specific Heat Capacity & Calorimetry
Do Now
1. What is the difference between heat and temperature?
2. What are the reactants and products in complete and
incomplete combustion?
3. In the pictures below describe the heat transfer process
that is occurring
Do Now
• Heat is the energy from the motion of
molecules, and temperature measures the
average speed of moving molecules
• Complete combustion:
CxHy + O2  CO2 + H2O
• Incomplete combustion
CxHy + O2  CO2 + H2O + C + CO
Do Now
Convection – fluids transfer
heat through movement
Conduction – heat is
transferred by molecules
vibrating and touching
each other
Objective
• I can calculate the energy contained in
different snack foods using a calorimeter and
the heat equation in a lab experiment and
report.
Agenda
1.
2.
3.
4.
Do Now, Objective (10 min)
Vocabulary Preview (10 min)
Calorimetry Lab (50 min)
Heat Notes (20 min)
Homework
• Complete Calorimetry Lab Report
– Show all calculations on a separate sheet of paper
– Use correct units of measurement at all times
DUE Friday!
Vocabulary Preview
• Thermochemistry: the study of heat effects that
accompany chemical reactions.
• When you measure the quantities of heat gained
or lost in chemical reactions you are investigating
the thermochemistry of those reactions.
• Endothermic: energy is ABSORBED by the system
from the surroundings
• Exothermic: energy is RELEASED from the system
to the surroundings
Lab Background
• Follow along as we read the Background
section of the lab as a class
• First Law of Thermodynamics: energy cannot
be created or destroyed, it can only change
form
Lab Background
Lab Background
• Calorimetry: the measurement of heat
transfer from one object to another.
• Today you will look
at how much heat is
transferred to water
when different snack
foods are burned as
fuel.
Lab Background
• Specific Heat Capacity: the heat energy needed to
raise the temperature of 1 g of a substance 1ºC.
– Water’s specific heat capacity = 1 cal/g ºC
Lab Background
• calorie: the amount of heat energy required
to raise the temperature of 1 gram of water
1ºC.
– 1 calorie = 4.184 J
– 1000 cal = 1 kcal
– 1 nutrition Calorie = 1 kcal
Calorimetry Lab
•
•
•
•
Work in groups of 3 – 4
Collect materials BEFORE you go outside
All lab write-ups must be done individually
Don’t play with burning food
Group Discussion
• What foods released the most energy?
• How can you tell these foods released more
energy?
• What do you think gives certain foods more
energy than others?
Heat Notes
• When fuels are burned they release heat
energy
Heat Notes
• The heat released when you burned snack foods
was used to heat water and raise its temperature
Heat Notes
• Heat and temperature are not the same thing
– Heat: a measure of the total energy in a system
(joules or calories)
– Temperature measures the kinetic energy (motion
of molecules) in a system.
Heat Notes
• A calorie is the amount of heat needed to
raise the temperature of 1 g of water 1ºC
– 1 calorie = 4.184 Joules
• 1 food Calorie = 1 Kcal = 1000 cal
Plicker Question
• How many Joules are in 3 calories?
a) 3000
b) 12.5
c) 0.7
d) 4184
Heat Notes
• To calculate the heat per gram of fuel used in
your lab, you need to know the specific heat
capacity of water
Specific heat capacity of water = 1 cal/g ºC
This is how much heat you need to raise the
temperature of 1 gram of water by 1ºC
Plicker Question
• How much heat, in calories, is required to
raise the temperature of 1 gram of water 5ºC?
a) 1 cal
b) 5 cal
c) 0.2 cal
Heat Notes
• You can determine how much heat energy is
released as a fuel burns with this equation
•
•
•
•
Q = mcΔT
Q = change in heat
m = mass of water in grams
c = specific heat capacity of water
ΔT = the change in temperature of the water
Practice Question
• When a peanut was burned, 25 grams of
water was heated from 10ºC to 30ºC. How
much heat (in calories) was released by the
peanut?
– Q = mcΔT
– Q = (25 g)(1 cal/gºC)(20ºC)
– Q = 500 calories (aka 0.5 Cal)
Heat Notes
• You can also calculate the energy content per
gram of fuel. This is done by dividing the heat
gain (Q), by the change in the mass of the
food sample.
• Energy content by mass = Q/Δmass
Plicker Question
• A 2 g marshmallow was burned, and remassed at 1.5 g. The burning marshmallow
raised the temperature of 6 g of water from
15ºC to 27ºC. What is the energy content per
gram of the marshmallow?
a)
b)
c)
d)
72 cal/g
36 cal/g
48 cal/g
144 cal/g
Heat Notes
• Endothermic reactions absorb heat
– It takes energy to break chemical bonds
– Endothermic reactions are absorbing energy to break
the bonds between atoms and molecules
• Exothermic reactions release heat
– Energy is released when bonds form
– This energy is stored in the chemical bonds of
molecules
– Exothermic reactions are releasing energy to form
new bonds between atoms and molecules
Plicker Questions
• Breaking chemical bonds is what type of
process?
a)
b)
c)
d)
Endothermic
Exothermic
Hypothermic
hyperthermic
Plicker Questions
• How much heat is required to change the
temperature of 150 g of water by 20ºC?
a)
b)
c)
d)
3000 cal
0.13 cal
7.5 cal
150 cal
Exit Ticket
• Answer the exit ticket silently at your table.
When you are finished turn it into the bin.