Understanding Heat Capacity of a Solid

Understanding the Heat Capacity of a Solid

Briana Gasperino, Michael Hyun, Khang

Submitted to: Shravan Uppala

General Chemistry 1045, Experiment 7, 4/4/18

Honor Code Signature: Briana Gasperino

Abstract.

        Heat capacity refers to the amount of heat energy needed to increase the temperature of a substance by one degree. Heat capacity can be studied through calorimetry, or the science of measuring the amount of heat released or absorbed through a chemical reaction. Through the use of a calorimeter, the specific heat capacity of copper, aluminum and an unknown metal sample was determined. The unknown metal was identified as zinc through the calculation of its molar mass using experimental data.

I. Introduction.

        Heat capacity is defined as the amount of heat required to raise the temperature of a substance by one degree Celsius or Kelvin2. Water has the highest heat capacity of any liquid, meaning it takes a greater amount of energy for it to cool down or warm up. This is because the water molecules are farther apart from each other and it is more difficult to separate or form molecular bonds. This is demonstrated by the slow rate at which relatively smaller bodies of water, such as lakes and ponds, freeze in the winter. This allows fish and other organisms to be able to survive at the bottom because temperatures are unable to reach low enough values in order to freeze the entire body of water. However, metals are relatively efficient in conducting heat, as they have low heat capacities. This is because molecules in solids are very close together, making it easier for heat to be transferred from atom to atom.

        Scientists have been studying energy and heat for hundreds of years, as energy is the source of all life and natural systems in our universe. Biochemical systems revolve entirely on the process of energy transfer, making this field of study essential for many different fields of science. Understanding heat capacity is useful in determining the boiling and freezing point of different substances. This has also allowed scientists to better predict the rate at which ocean levels will continue to rise in coming years due to global warming and increasing pollution of the environment.

In this experiment, we analyzed the specific heat capacity of copper, aluminum, and an unknown metal. This was accomplished by heating the metals in boiling water, place the hot metals in a calorimeter containing cold water, and measuring the initial and final temperatures of the calorimeter. The Law of Conservation tells us that energy cannot be created, nor can it be destroyed3. From this information we can conclude that the amount of heat lost by the metals is equivalent to the amount of heat gained by the water. This allowed us to determine the hat capacity the metals. Additionally, the Law of Dulong et Petit, which states that the molar heat capacity of any solid element is equal to approximately 3R, where R the universal gas constant 8.314 Joules per mole per degree temperature3. This law was used to determine the molar mass of the unknown sample, and therefore identity the substance.

II. Experimental.

Procedure:

 _        The first step in the experimental procedure is to make an ice bath, consisting of mostly ice, in a 400 mL beaker. The temperature probe must then be calibrated to have a reference point of 0.0 °C for the ice bath. Each metal sample should be weighed, and the mass recorded in grams. Fill a 250 mL beaker with approximately 100 mL of water and place the beaker on a wire-gauze on a tripod. Bring the water to a boil using a Bunsen Burner. Once the water begins to boil, carefully place the Aluminum and Copper samples into the water using tongs. After the metals have been in the boiling water for approximately 10 minutes, measure the temperature of the water using the temperature probe. This value should be used as the initial temperature of the two metals. Next, fill a polystyrene calorimeter with a mass of water that is double the mass of whichever metal you are measuring. The temperature of the water in the cup should then be measured and recorded as the initial water temperature. Using tongs, remove the metal from the boiling water and place the metal into the calorimeter. Cover the cup with a plastic lid and stir the water with the temperature probe by inserting it through the hole in the lid. Record the maximum temperature that was reached. The above steps should be repeated several times with each metal sample.

Data:

• Table 1. Mass of Metal Samples

• Table 2. Recorded Temperatures of Metal and Water

Observations:

The copper was a long, brown cylinder shape and felt significantly greater in mass than the aluminum sample. The aluminum was the same size and shape, however it had a bronze color. The unknown metal was a short cylinder shape and it had a dark brownish-bronze color. Upon placing the heated metals in the water, the temperature fluctuated rapidly until it began to steadily decrease.