Specific Heat
COLLEGE PHYSICS LABORATORY
PH 141
Thermal Properties of Matter
Specific Heat Capacity
Purpose:
To verify that for all objects made of the same substance, the heat capacity of an object is
proportional to the mass of the object. To verify that the specific heat capacity of a
substance is a characteristic property of the substance. To practice the reasoning
performed in calorimetry experiments.
Discussion:
When substances at different temperatures are brought into contact they experience
thermal interaction. During this interaction heat is lost by the warmer substance and
gained by the cooler substance. This process continues until both substances are at the
same temperature. When heat is gained or lost by a substance (and there is no phase
change of the substance), the temperature of the substance rises or falls in accordance
with the following relationship:
∆
(1)
Q represents the quantity of heat transferred, T represents the temperature change, and C
represents the heat capacity. The heat capacity indicates how much heat must be gained
or lost by a system to result in a temperature change of 1 .
The heat capacity of a system depends on two factors: the kind of substance(s) that make
up the system (composition) and the amount of substance (mass). This generalization can
be summarized as the following relationship:
(2)
The variable "m" represents the mass of substance, and "c" represents the specific heat
capacity of the substance. The specific heat capacity indicates how much heat must be
gained or lost from 1 gram of substance to result in a temperature change of 1 .
Method:
In this experiment you will determine the heat capacity for various amounts of iron. A
simple way to vary the amount of iron is to measure the heat capacity for different
numbers of iron washers.
Specific Heat
To determine the heat capacity for each number of washers use the following procedure.
Use about 50 g of room temperature water in a Styrofoam cup and record the
temperature. Place the washers in a water bath, either hotter or colder than room
temperature, until the iron has come to equilibrium with the water bath. Then quickly
transfer the washer to the water and allow the water + washer system to come to
equilibrium. Measure and record the final equilibrium temperature.
Do this experiment for several different numbers of washers. For the smallest and the
largest numbers of washers, do the experiment three times.
From the mass of the water and the temperature change of the water you can determine
the amount of heat in calories gained/lost by the water. One calorie is the amount of heat
required to change the temperature by 1 of one gram of water.
This amount of heat is lost/gained by the iron washers. From the heat lost/gained and the
temperature change you can determine the heat capacity of the iron washers.
Analysis:
1. For each experiment determine the heat capacity of the object. Record these values as
well as the mass of the object in a table. [Note: The symbol we are using for heat capacity
is big "C," whereas the symbol that we and the book will use for specific heat is little
"c."]
2. Make a graph of heat capacity versus mass of the iron. USE GRAPH PAPER. Should
the graph go through the origin of the graph? Make sure the origin is on your graph.
3. Draw a "best fit" line for your data. Give an interpretation of the slope of the graph in
terms of the heat capacity. What is the significance of the observation that the graph is a
straight line?
4. Give an interpretation of the slope without mentioning heat capacity. That is, give an
interpretation in terms of heat, temperature change and mass.
5. How does your value for the specific heat of iron compare to the standard value
reported in your text (ciron = 0.11) ? Express as a percent difference.