COLLEGE PHYSICS LABORATORY
PH 141
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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:

Q = CDT

Q represents the quantity of heat transferred, DT 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 Co.

The heat capacity of a system depends on two factors: the kind of substance(s) that make up he system (composition) and the amount of substance (mass). This generalization can be summarized as the following relationship:

C = mc

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 Co.

 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.

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 washers to the water and allow the water + washers 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 1Co 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 cal/(Co g)? Express as a percent difference.