Heat Calculations
Agenda
• Review specific heat
• Look at lab sections
• M&M and Results
• Learn about heating curve
What is specific heat?
The energy to raise one gram of a
substance one degree Celsius.
What has a higher specific
heat: the ocean or the beach?
The OCEAN – it takes a lot of energy
to warm it up!
What has a higher specific
heat: aluminum foil or the
glass pan?
The GLASS PAN – holds the heat for
a much longer period of time
Define energy.
The ability to do work!
When a reaction releases
energy in the form of heat, it
is said to be…
EXOTHERMIC
This means it’s negative!
When a reaction absorbs
energy in the form of heat, it
is said to be…
ENDOTHERMIC
This means it’s positive.
What is the formula for
finding heat?
q = m*s*DT
What are the different units
used to measure energy?
Joule and Calorie
Related?
1 cal = 4.184 J
What happens if there is a
phase change?????
This is where the heating curve
comes in…
Heat Calculations
Date:
T
E
M
P
E
R
A
T
U
R
E
E N E R G Y
T
E
M
P
CONDENSE
E 100OC
VAPORIZE
R
A
T 0OC
FREEZE
MELT
U
R
E
E N E R G Y
T
E
M
P
CONDENSE
E 100OC
VAPORIZE
R
A
T 0OC
FREEZE
MELT
U
ENDOTHERMIC g
R
EXOTHERMIC f
E
E N E R G Y
T
E
M
q = m*DHvap
P
DHvap = 540cal/g
CONDENSE
E 100OC
R
A
T 0O
C
U
q = m*DHfusion
VAPORIZE
DHfusion = 80 cal/g
FREEZE
MELT
ENDOTHERMIC g
R
EXOTHERMIC f
E
E N E R G Y
Solving Problems
 Read question and determine number of
“lines” involved.
 Calculate the amount of heat required for
each “line”
 Determine the sum of all “lines” used.
 IF ENERGY IS RELEASED, you MUST
make DHfus and DHvap negative!!!!
Calculate the amount of heat necessary to raise
20g H2O from -10oC to 45oC
 Determine lines:
-10oC = solid, 45oC = liquid so 3 lines used.
 Solid: q = m*sice*DT
q = (20g)(0.5cal/goC)(0oC – (-10oC)) =
 Melt: q = m*DHfus
q = (20g)(80cal/g) =
 Liquid: q = m*sliquid*DT
q = (20g)(1cal/goC)(45oC – 0oC) =
TOTAL AMOUNT OF HEAT =
Calculate the amount of heat released when 30g
H2O are cooled from 115oC to 65oC
 Determine lines:
65oC = liquid, 115oC = gas so 3 lines used.
 Gas: q = m*sgas*DT
q = (30g)(0.4cal/goC)(100oC – 115oC) =
 Condensed: q = m*DHfus
q = (30g)(-540cal/g) =
 Liquid: q = m*sliquid*DT
q = (30g)(1cal/goC)(65oC – 100oC) =
TOTAL AMOUNT OF RELEASED HEAT =
Suppose the heat needed to melt 38.0g of ice is
absorbed from water contained in a glass. If this
water has a mass of 210. g and an initial temperature
of 21.0oC, what is the final temperature of the water?
Remember the ice melts and then warms up as a
liquid.
Check homework
Lab
 M&M:
– how was calorimeter constructed
– when were temperature and mass readings made –
not what but when
– don’t list supplies
– does it make sense – can you picture the lab like a
movie
 Results: Charts
– Data used for calculations – Table 1
– Temperature over time GRAPH!!!!! Graph 1
– Show a sample calculation (q = msDT)
Metal sample
Mass of metal
Volume of water
Mass of water
T I metal (Boiling water)
T I water/calorimeter
T f system
DT metal
DT water/calorimeter
s water
q water
q metal
s metal
Homework
 Heat Calculations worksheet
 Make corrections to MM and Results
– Put data into spreadsheet from wiki
 Work on conclusions