Specific Heat Capacity Lab PDF

Preview

Summary

lab write-up...

Description

1 Specific Heat Capacity Lab SPH 3U1 Thursday, April 13, 2017 Introduction All matter is composed of particles that are in constant motion, according to the Kinetic Molecular Theory. This constant and random motion gives each particle kinetic energy (the energy of motion). The total kinetic energy of all the atoms or molecules in a substance is known as thermal energy. Thermal energy depends on a number of factors such as the mass of the sample (number of molecules), the temperature (vibrations), and the kind of substance (material, density, crystal structure, etc.). This number can never be calculated to the perfect amount as particles are very, very tiny and it is impossible to know the exact amount in a sample. Additionally, each particle may be moving at a slightly different rate than the ones around it, making it all the more difficult to calculate an exact value. Thus, the average kinetic energy of the atoms in a substance can be measured through temperature. Different scales of temperature include Celsius (℃), Fahrenheit (℉), and Kelvin (K). Average thermal energy, Eth measured in Joules, can be calculated using the following formula: Eth = mct In the above formula, ‘c’ represents the specific heat capacity of a substance. This is the amount of heat or Joules that is required to raise one kilogram of the system’s temperature by one kelvin, expressed in J/(kgK). Thus, by multiplying by mass and the temperature, the current amount of thermal energy can be found. Moreover, the transfer of this thermal energy from a warmer body to a cooler body is know as heat (Q). There are different methods of heat transfer: conduction, convection, and radiation. Conduction is the collision of atoms that transfers the heat through materials that are in contact. Convection transfers heat by a circulatory path of fluid (gas or liquid) particles and radiation transfers heat using electromagnetic waves. As heat is the transfer of thermal energy, Q can be represented by ΔEth. Due to this transfer of heat, the temperature of the objects change as well, giving Δt. Thus, the following equation can be derived: Q = mcΔt

2 Furthermore, energy can never be destroyed or created. Hence, in a heat transfer, the amount of heat lost from one or more objects must be gained in the same proportion in another object. Thus, the principle of heat exchange encompasses this rule and provides the following formulas which are very useful when calculating for energy and temperatures: Q1 = Energy Lost (negative number), Q2 = Energy gained (positive number) Q1+Q2= 0

or

Q1= -Q2

m1c1(tf -t1) + m2c2(tf -t2) = 0 Using all of these connections and equations, many different things can be calculated for, given enough data is present. The equations can also be manipulated to calculate for different values. For example, by studying the temperature change in two different objects in contact and the transfer of energy, the specific heat capacity of one of the objects can be found using the principle of heat exchange. Purpose To measure the heat capacity of different materials. Hypothesis I believe that the darker and duller metals will have a lower value of specific heat capacity than metals that are lighter and shinier. As they are dull and dark, they should be able to capture more heat energy and get hotter faster. They can also emit heat at a faster rate, hence cooling down faster. Shinier metals will not allow the heat to pass through as easy, acting like insulators. Once they are hot, they will also not cool down as easy. This concept can be seen in the transfer of heat due to radiation. A dark and dull container holding hot liquid will feel hotter on the outside than a shiny container holding the same amount of equally hot liquid. Due to this thinking, I presume that the duller and darker metals will have a lower heat capacity than the shiny and light metals. Procedure Procedures outlined in provided booklet were followed. Observations -The initial temperature of the metals is 100℃, and decreases to the final temperature of water. Sample

Mass

Mass of Empty

Mass of

Mass of

Initial

Final

3

Material

of Sample (kg)

Calorimeter with stirrer (kg)

Calorimeter with water (kg)

water (kg)

temperature temperature of water of water (℃) (℃)

Nickel (Silver colour, very shiny)

0.0615

0.0579

0.1570

0.0991

23.4

27.5

Unknown (Dark colour, dull)

0.0546

0.0579

0.1580

0.1001

23.8

27.0

Unknown (Golden colour, slightly shiny)

0.0675

0.0579

0.1582

0.1003

23.6

27.4

Analysis The principle of heat exchange, Q1+Q2+Q3= 0, can be used to calculate for the specific heat capacities of each metal in the different tests as shown in the following charts: (Information from the observations was copied into their respective places in order to organize the information to perform calculations) Test One: Nickel Object

Calorimeter with stirrer

Water

Metal Cube (Nickel)

Mass (kg)

0.0579

0.0991

0.0615

Initial Temperature (℃)

23.4

23.4

100

Final Temperature (℃)

27.5

27.5

27.5

Specific Heat Capacity (J/kg℃)

920

4180

Q3 = mcΔt -1918 = c(0.0615)(-72.5) c = 430

Heat Exchanged (J)

Q1 = mcΔt = (0.0579)(920)(4.1) = 218

Q2 = mcΔt Q1+Q2+Q3= 0 = (0.0991)(4180)(4.1) 218+1700+Q3= 0 Q3 = -1918 = 1700

After filling in all of the blanks in the chart, the heat capacity of nickel came to be 430 J/kg℃. This value seems to be reasonable as most metals have heat capacities in the couple hundreds.

4 Additionally, nickel’s heat capacity is actually 440 J/kg℃, which is quite close to the calculated value (UCDSB, n.d.). Thus, the calculated heat capacity must be correctly derived as it is close enough when considering human and lab errors. Test Two: Unknown Object

Calorimeter with stirrer

Water

Metal Cube (Unknown)

Mass (kg)

0.0579

0.1001

0.0546

Initial Temperature (℃)

23.8

23.8

100

Final Temperature (℃)

27.0

27.0

27.0

Specific Heat Capacity (J/kg℃)

920

4180

Q3 = mcΔt -1510 = c(0.0546)(-73.0) c = 379

Heat Exchanged (J)

Q1 = mcΔt = (0.0579)(920)(3.2) = 170

Q2 = mcΔt Q1+Q2+Q3= 0 = (0.1001)(4180)(3.2) 170+1340+Q3= 0 Q3 = -1510 = 1340

After filling in all of the blanks in the chart, the heat capacity of this unknown metal came to be 379 J/kg℃. Many metals seem to be in this range, but when analyzing the physical properties of this sample, it is most likely to be zinc. Zinc is dark in colour and not too shiny, just like the sample metal that was used. It also has the closest heat capacity at 388 J/kg℃, proving that this sample metal must be zinc (The Engineering Toolbox, n.d.). Other metals either do not match up physically or do not have a close enough heat capacity to identify as this unknown metal. Test Three: Unknown Object

Calorimeter with stirrer

Water

Metal Cube (Unknown)

Mass (kg)

0.0579

0.1003

0.0675

Initial Temperature (℃)

23.6

23.6

100

Final Temperature (℃)

27.4

27.4

27.4

Specific Heat

920

4180

Q3 = mcΔt

5

Capacity (J/kg℃) Heat Exchanged (J)

-1792 = c(0.0675)(-72.6) c = 366 Q1 = mcΔt = (0.0579)(920)(3.8) = 202

Q2 = mcΔt Q1+Q2+Q3= 0 = (0.1003)(4180)(3.8) 202+1590+Q3= 0 = 1590 Q3 = -1792

After completing the chart using the principle of heat exchange, the heat capacity of this unknown metal came to be 366 J/kg℃. Judging by the appearance of having a golden brown colour, it is most likely to be brass. Brass also has a very close heat capacity of 375 J/kg℃, proving that this sample metal must be brass (The Engineering Toolbox, n.d.). Out of the given metal cubes, brass is the most likely to be the one used as it matches up with both physical aspects and with the value of heat capacity. Results Through analyzing many aspects of each metal, the following results have been derived to allow for the least discrepancy between values: Metal

Nickel

Zinc

Brass

Calculated Value of specific heat capacity (J/kg℃)

430

379

366

Researched Value of specific heat capacity (J/kg℃)

440

388

375

− T heoretical | Percent Difference = || Experimental T heoretical | × 100%

2.27%

2.32%

2.40%

Discussion The calculations performed on the data and charts extracted many different values.When the different heat capacities are compared to each other based off of their metal’s physical properties, there are not many patterns seen. Hence, the hypothesis that stated duller and darker metals should have a lower heat capacity than the shiny and light metals has proven to not be completely correct. For example, when the metals are ordered based off of their heat capacity going from highest to lowest, the resulting order is: nickel, zinc, and brass. In this sample, zinc is the darkest and most

6 dull metal, as seen in Fig. 1. However, zinc does not have the lowest specific heat capacity, as was hypothesized. When trying to find patterns, the metals can also be classified by their density from most dense to least: nickel, brass, and zinc. However, this order does not yield any answers either as the heat capacities do not fall in any type of pattern through this feature. In the end, the specific heat capacity of a metal depends on a number of factors, such as the amount of substance, the different types of bonds it has, impurities in the sample, in some cases the temperature, the physical appearance, and the phase the metal is in (Wikipedia, 2017). The resulting heat capacities that were calculated through this lab were very close to their actual heat capacity, being only a bit over two percent off each time. Considering many factors such as procedure, equipment quality, and human error, this percent deviation is very small and can be easily explained when reflecting back on the activity. There are a number of factors affecting the results of the experiment. Firstly, the equipment that was used during the lab may not be of the best quality. For example, the calorimeter was not a professional type, only a classroom version. The sealing and insulation is good enough for student use, but not completely foolproof. This difference in quality in the calorimeter affected the results to be different than the expected value, resulting in a percent deviation. Furthermore, the thermometer that was used may not be completely accurate when reading temperature. In this lab, a difference of 0.01℃ in temperature can make a huge impact on the calculated results. Hence, the thermometer could have rounded and gave a temperature reading that was 0.01℃ off or the thermometer could have been read too early due to human error, giving inaccurate results. Moreover, the metal cubes that were used may have some impurities. These impurities impact the properties of each metal cube, causing it to react and behave slightly differently. For example, the density of the actual cube could have been different than what the metal should be, changing the mass of it and thus the calculations. Additionally, these impurities would affect the metals ability to give off heat, affecting the resultant heat capacity for that sample. Impurities are commonly present and, with no exception, they do affect the results to some degree. Lastly, a procedure error could be that the metal cubes were not placed in the boiling water long enough. The cubes may not have been able to internally reach a temperature of 100℃ in the given time, giving false calculations as the written information

7 would actually be wrong. These are all valid aspects that affected the final results, causing a percent deviation between the actual value and the experimental one. All the percent deviations were in the same range, between 2.25% to 2.40%, meaning that the aspects affecting the results were consistent in their presence. An improvement for future use is to consider using equipment of better quality. Perhaps newer or better calorimeters could be used, thermometers with a higher degree of accuracy be invested into, or metal cubes with fewer impurities could be researched for and bought as replacements. Additionally, when reading the temperature, more patience could be practiced to allow the thermometer to settle to the actual degree of the material. These are all valid steps to improve lab results and ensure more accurate answers are derived. Furthermore, it would be wiser to leave the metal cubes in boiling water for a longer period of time. This would help the whole metal cube warm up to the documented temperature, allowing for a better performance during the actual activity. This way, a different final temperature would be recorded, altering the final results. With these investments and tips, the percent deviation between the calculated heat capacity and the expected heat capacity will surely decrease immensely. Conclusion In conclusion, the purpose of this lab was to measure the heat capacity of different materials. This purpose was achieved and the heat capacities for the different metals came to be: 430 J/kg℃ for nickel, 379 J/kg℃ for zinc, and 366 J/kg℃ for brass. Additionally, zinc and brass were actually the guessed metals for those results, as they had the most similar physical aspects and expected heat capacity when compared to the unknown metal. Overall, the results were quite accurate to the expected values with only a 2.25%-2.40% discrepancy depending on which test was looked at. The hypothesis was learned to be incomplete, as the heat capacity actually depends on a number of factors within the sample such as the amount of material and internal bonds, not only the outside colour and lustre. Additionally, many errors were explored with suggested improvements for each one. Therefore, the purpose of this lab was successfully achieved and a few lessons at proper data recording were learnt as well. Application

8 Heat exchange is extremely important and commonly used in the world in a number of applications. Many new technologies are being developed that also use heat exchange to benefit the society in a number of ways. One example is thermal banks, an integral part of an Interseasonal Heat Transfer system developed by ICAX that eliminates the need to burn fossil fuels. A thermal bank is “a bank of earth used to store heat energy collected in the summer for use in winter to heat buildings”. Seven metres into the earth, the movement of heat is slowed down to almost one metre a month (most likely due to a very high specific heat capacity), making it a prime area to store warm temperatures over a period of a few months. ICAX uses this characteristic to store surplus heat into the ground over the course of the summer, extracting it once winter comes around and heating is needed in buildings. This Interseasonal Heat Transfer functions by capturing heat energy from the sun by a collection pipe network just beneath the surface of black tarmac roads, parkings, or school playgrounds, as seen in Fig. 2. Tarmac roads absorb the sun’s heat right up till the point that they radiate heat as quickly as they are absorbing it, an excellent example of radiation heat transfer. On average, the surface temperature of tarmac can reach up to 15℃ higher than the air around it (ICAX, n.d.). With a specific heat capacity of only 920 J/kg℃, which is quite low compared to a lot of materials, tarmac is great at capturing energy quickly (The Engineering Toolbox, n.d.). Then, the energy from the pipe network under the tarmac is stored in computer-controlled thermal banks that are located under the foundation of buildings, releasing it via heat pumps linked to underfloor heating in the winter. In the U.K, seven metres underground, the temperature is normally very close to 10℃, varying only by a little between summer and winter as heat moves extremely slowly in the ground. The thermal bank can increase the natural temperature of 10℃ to over 25℃ over the course of the summer. Fluids are used, in an array of pipes, to transport the heat into the ground and back out again, reducing many difficulties. Although the system in which heat is absorbed and released through the ground is very complex,

9 it is a very eco-friendly way to heat up a building. It allows a total of 50% savings on carbon emissions compared to getting heat from gas boilers, making it a very efficient and beneficial system to invest into (ICAX, n.d.). The functions of heat capacity have been greatly used in this system, as seen through both the tarmac and the deep ground. Tarmac, with a low heat capacity, easily gains energy from the sun which fuels this entire system. The deep ground, with a high heat capacity, holds onto the energy it is given, due to the long time it takes for heat to transfer to different areas of the ground, right up until it is taken out.

10 References Heat capacity. (2017, May 08). Retrieved May 08, 2017, from https://en.wikipedia.org/wiki/Heat_capacity#Factors_that_affect_specific_heat_capacity Specific Heat Capacity Table. (n.d.). Retrieved May 08, 2017, from http://www2.ucdsb.on.ca/tiss/stretton/database/specific_heat_capacity_table.html Specific Heat of common Substances. (n.d.). Retrieved May 08, 2017, from http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html ThermalBanks™ store heat between seasons. (n.d.). Retrieved May 09, 2017, from http://www.icax.co.uk/thermalbank.html...