Unit 1: Chemistry Basics
1.52 Calorimetry
Textbook ch 5.5
© 2009,
Prentice-Hall, Inc.
Big Idea 5: The laws of thermodynamics describe the essential role of energy
and explain and predict the direction of changes in matter. Students will be
able to demonstrate understanding by laboratory investigation, analysis of
data and creation of models.
Learning Objectives
:
SWBAT:
•Calculate the heat transferred in
a process from temperature
measurements together with
specific heat capacities
Calorimetry is Another Way to
Measure H values
We measure H through calorimetry, which measures heat flow
Two types of calorimetric or energy equations
1) Within a Phase –
• These will have a change in temperature but will stay the
same phase (solid, liquid, or gas) the whole time
• Also known as specific heat calculations using a
calorimetry
2) At a Phase Change –
• These will have a constant temperature but will change
phase (ex: solid to liquid)
(We will worry about this one in the next video.
Calorimetry
• Measuring heat.
• Use a calorimeter.
• Two kinds
– Coffee cup calorimeter
and
– Bomb calorimeter (Not
used on AP test)
© 2009,
Prentice-Hall, Inc.
Coffee Cup Calorimetry
• One can indirectly measure
the H for the system by
measuring the heat change
for the water in the
calorimeter.
• Heat =q = m x c x T
• A coffee cup calorimeter
measures H.
H = qreaction /# moles
• An insulated cup, full of
water.
• The specific heat of water
is 4.18 J/gºC
© 2009,
Prentice-Hall, Inc.
Specific Heat
Definition: The
amount of heat
required to raise the
temperature of one
gram of substance
by one degree
Celsius.
5
4
6
5
7
4
3
8
3
2
9
2
1
11
6
7
8
9
1
10
Calculations Involving Specific
Heat
( Remember: Phase stays the same the entire time. Ex. always a liquid.)
q = mcT
q = Heat lost or gained
m =mass
c = Specific Heat Capacity
T = Temperature change
Units for specific heat (c) are:
Joules
(gram) (Celsius)
Examples within a phase
Example 1: 5.83g of water was heated from
25.0ºC to 79.0ºC. The specific heat of water = 4.18 J/gºC
How much energy was required to heat this sample?
Given
q=
m=
c=
ΔT =
q = m · c · ΔT
Example 2: A block of ice was heated from
-30.0ºC to -15.0ºC. It required 181J of heat for this to occur. The
specific heat of ice = 2.06 J/gºC
What was the mass of the block of ice?
q = m · c · ΔT
Example 3: A silver block (c = 0.235 J/gºC) weighing
10.5g was at 81ºC. It was then dropped into a
container of hot liquid, and it absorbed 250.J of heat.
What was the final temperature of the silver block?
q = m · c · ΔT
How do you calculate if it’s a solution?
Same equation
q = mcT
q = Joules of heat
m = total mass in calorimeter (solutes +solvent)
(If a solution, use m = D * V to obtain the mass)
Water has a density of 1.00 g/mL. We will assume
the density of the solution is near that of water.
(Write that statement on AP test!)
c = specific heat (for water, 4.18 J/g-K)
T = Tf - Ti
A student performs an experiment to determine the molar enthalpy of solution of
urea, H2NCONH2. The student places 91.95 g of water at 25°C into a coffee-cup
calorimeter and immerses a thermometer in the water.
After 50 s, the student adds 5.13 g of solid urea, also at 25°C, to the water and
measures the temperature of the solution as the urea dissolves. A plot of the
temperature data is shown in the graph below.
(a)
Determine the change in
temperature of the solution that results
from the dissolution of the urea.
(b)
According to the data, is the
dissolution of urea in water an
endothermic process or an exothermic
process? Justify your answer.
(c)Assume that the specific heat capacity
of the calorimeter is negligible and that
the specific heat capacity of the solution
of urea and water is
4.2 J g-1 °C-1 throughout the experiment.
(i) Calculate the heat of dissolution of the
urea in joules.
(ii) Calculate the molar enthalpy of
solution, H
© 2009,
Prentice-Hall, Inc.
References
http://www.sciencegeek.net/Chemistry/Powerpoints2.shtml
I modified the original PPT to fit our needs in AP Chemistry needs.
Our textbook: Brown, Lemay et all. AP edition
chemistry, 13th edition, 2015