U3 S1 L3
Constant Pressure Calorimetry.
Textbook Readings MHR
•pages 661-664: The Technology of Heat Measurement
Textbook Practice Items MHR
•pages 664-665: items 1, 2, 3, and 4
•Homework Postings: last page.
Upon completion of this lesson, you should
be able to:
• define the calorimeter and identify it as
the basic instrument for measuring heat
transfer
• calculate the heat gained by or lost from a
system using the formulas q=mc∆T
and/or q = c∆T
•
Calorimetry
Calorimetry is the measurement of heat changes.
–
•
It is carried out using devices called calorimeters.
Calorimetry is based on the idea that energy lost by a system equals the
energy gained by the surroundings and vice versa; in other words, it is
based on the first law of thermodynamics.
qsys = - qsurr
•
There are two basic types of calorimeter:
1. constant pressure (or simple calorimeter or coffee-cup calorimeter)
•
The water in the calorimeter is the surroundings
qsys = - qwater
2. constant volume or bomb calorimeter.
•
the calorimeter is the surroundings,
qsys = - qcalorimeter
Constant Pressure Calorimeter (simple calorimeter)
Bomb Calorimeter
•
The simple calorimeter consists of an insulated container, a
thermometer, and a known amount of water (see Figure 17.1
on p.661 of MHR).
•
It is used to measure heat changes associated with heating,
cooling, phase changes, solution formation, and chemical
reactions that occur in aqueous solution.
•
you will assume that when an energy change occurs in a
simple calorimeter, the calorimeter water absorbs or releases
all of the energy associated with the change.
•
In other words, the calorimeter (specifically the calorimeter
water) takes on the role of the surroundings.
Cwater=4.19 J/gC
•
The final temperature of the system and surroundings will be
the same.
Tf is the same for the system and the surrounding.
1.
A very cold piece of silver with a mass of 78.41 g is added to a simple calorimeter that
contains 150.0 g of water. The temperature of the calorimeter water changes from 19.73°C
to 16.11°C. (The specific heat capacity of silver is 0.24 J/g°C.)
a.
b.
Calculate the heat change for the piece of silver.
How cold was the piece of silver?
2. A simple calorimeter with a heat capacity of 1.05 kJ/°C undergoes a decrease of
1.56°C when a very cold piece of iron is added to it. Calculate the heat change of
the iron
3. A simple calorimeter contains 150.0 g of water. A 5.20 g piece of an alloy at
525.0°C is dropped into the calorimeter causing the temperature of the calorimeter
water to increase from 19.30°C to 22.68°C. Calculate the specific heat capacity of
the alloy.
4. The temperature in simple calorimeter with a heat capacity of 1.05 kJ/°C changes
from 25.0°C to 23.94°C when a very cold 12.8 g piece of copper was added to it.
Calculate the initial temperature of the piece of copper.
5.
A new ceramic material underwent for use as an insulator. Part of the analysis
involved determining its specific heat capacity. A 20.00 g sample was heated to
200.0°C and added to a simple calorimeter with a heat capacity of 1.46 kJ/°C.
The temperature in the calorimeter changed from 24.87°C to 27.15°C. Calculate
the specific heat of the ceramic material.
6.
A new composite material used in airplane construction was being
analyzed in order to prepare a detail list of its physical properties.
Describe the procedure you would use to determine its specific heat
capacity.
Homework – postings u3s1L3:
1. Gold has a specific heat capacity of 0.129 J/g.C
(a) How much heat will a piece of gold having a mass of 5.00 g transfer
when it changes temperature by 50.0oC? (ans:32.3)
(b) If this 5.00 g piece of gold is placed into 10.0 g of water, what
temperature change will occur in the water for the 50.0oC change in the
gold?
(ans: 0.77oC)
2. A calorimeter designed to have negligible heat loss is used to determine the
specific heat capacity of metals. A piece of thallium having a mass of 111.2 g
is warmed to 95.0ºC and placed into the calorimeter containing 125.00 g of
water at 12.5ºC. The water temperature goes up to 14.9ºC. Use this
information to calculate the specific heat capacity of thallium. The specific
heat capacity of water is 4.184 J/g·ºC.
(ans:0.14 j/g.C)