Significance of Knowing Specific Heats of Construction Materials - Term Paper Example

The Significance Application of Knowing Specific Heats of Construction Materials Overview Every so often in life, people all over the world have become accustomed to building structures normally for a crucial aim of establishing homes, work places, recreational facilities, and industrial units by which to live and improve the quality of life. One is essentially shed the light of understanding why engineering and architecture are fields of great professional worth when it comes to designing processes and selecting materials that would constitute the foundation of a structure being erected. To me, it is rather fascinating how engineers are able to estimate strength and weakness of materials and account for thermodynamic properties that collectively make a huge factor so that specialists may gain idea of whether a project is bound to succeed or fail, based on the test of time and weather. Among the properties that matter in thermodynamics and the principles applied hereby, specific heat of a substance occurs to be one of the most significant, particularly as it relates to heat, being itself the quantity of heat required for a unit mass of the substance to experience a degree of temperature change. Analyzing this truth in association to a changing weather should make us ponder on the connection between specific heat and the capacity of an object to withstand real climatic variations. It appears that the higher a material’s specific heat is, the more that such material is capable of holding large amounts of energy, in the form of heat, prior to weakening or wearing down by external forces of nature. Hence, engineers calculate and design hand-in-hand with thermodynamic concepts and prefer schemes where building structures can be optimized with materials that possess ideal specific heat capacities in order to carry out tasks that would be disposed to reduce any future risks of unexpected breakage, impairment, or deterioration when allowable stress or strain is exceeded due to materials that have not been properly assessed in terms of heat capacity. Through the First Law of Thermodynamics which is mathematically stated by – ?U = Q + W we gain fuller comprehension of how energy is conserved as heat and work, being each a form of energy, becomes a sum equivalent to the internal energy of a system in a material dealt with. In materials used for construction such as metal, concrete, glass, sand, or gravel, the stresses which any of these can either bear or not are altogether identified via heat (Q) and work (W) in and out of the system. Thus, considering the sensible ‘Q’ property, especially one that deals with temperature change, specific heat serves a critical tool that partly enables an engineering professional to decide which materials make an exquisite choice. Eventually, a calorimetric approach of determining an object’s specific heat, if initially unknown in literature, turns out to be an interesting piece of endeavour. In this regard, a thermodynamic process can be improvised for analysing specific heats of commonly utilized construction materials (as metal and sand) in a comprehensive and systematic simple experimental procedure. Determination of Specific Heat of Metal and of Sand Problem Statement / Purpose Determination of specific heats of certain materials can be carried out in a basic setting in which only heating and measuring temperature are the only tasks involved on the assumption that the value of the heat or energy used is derived from a power input typically in Watts or J/s. The objective of the experiment is to find out the specific heats of metal and sand, respectively, by having each substance reach a certain temperature when on heating. Each heated substance would be placed in a calorimeter containing water (independent setup for each of metal and sand) where temperature change of water would be monitored under time intervals until it stabilizes to a maximum equilibrium temperature. Background The specific heat of any material determines the amount of energy needed to heat 1 gram of substance by 1 degree Celsius which is obtained through the equation Q = m*C*?T where ‘m’ refers to the mass of material, C is the specific heat and ?T is the change of temperature. ?T in Kelvins is the same in magnitude as ?T in Celsius, hence, the specific heat for water may also be reported in J/g-°C (literature values: specific heat of metal lead = 0.128 J/g-°C; specific heat of quartz sand = 0.795 J/g-°C). Because the specific heat values for a given substance can vary slightly with temperature, the temperature is often precisely specified. What to Prepare metal sample (lead beads) and sand weighing device 600-mL beaker wire screen water hot plate test tube and test tube clamp iron stand calorimeter and thermometer stirring rod timer Procedure For Specific Heat of a Metal Fill a 600-mL beaker about halfway with water and place it on a wire screen that is supported on a ring stand. Heat the water to a boil using a hot plate. Find the mass of a large test tube and stopper using a balance. Add enough lead beads to the test tube to attain a mass of lead beads around 50g. Record the mass of the lead beads on the data sheet. Clamp the test tube to the ring stand so that it is suspended in the boiling water. Heat the lead beads with the boiling water and monitor the temperature of the beads. Be extra careful when using a thermometer, do not leave it unattended. Obtain a calorimeter and fill it with 100.0mL of water. Put the lid on the calorimeter, insert a thermometer, and record the exact temp. Once the temperature of the lead beads has reached approximately 98°C. Record the exact temp, and quickly pour the hot beads into the calorimeter. Place the lid on the calorimeter, note the time, and begin stirring with a stirring rod. Record the temperature at 15 seconds, then 30 seconds. Continue to record the temperature every 30 seconds for 5 minutes. During this time the water will reach its maximum equilibrium temperature. This is the temperature that should be used in the calculations. Decant the water out of the calorimeter, making sure not to lose any solid beads down the drain. Then pour the lead beads into a recovery tray so that they can be dried. Repeat this procedure if required by instructor. If two trials are performed find an average of the specific heat values. Then determine the percent error associated with the experiment. For Specific Heat of Sand Using the same boiling water bath for the specific heat determination was used for the lead determination. It is quite possible that more water will need to be added. Add about 50g of sand to the large test tube and obtain the exact mass of sand. Suspend the test tube in the boiling water bath and heat vigorously for several minutes until the temperature of the sand reaches about 98degrees C. Record the temperature. Set up the calorimeter once again, making sure that it contains exactly 100.0mL of water and is equipped with the lid. Record the stabilized temperature of the water in the calorimeter. Carefully and quickly add the hot sand to the calorimeter and cover the lid. Stir with a stirring rod and monitor the temperature for 5 minutes over 30-second intervals. Again, use the highest equilibrium temperature for the determination of the specific heat. Data Sheet Data Sheet for Specific Heat of Metal Mass of test tube 56.93 Mass of metal 50g Volume of water 100mL Mass of Water 100g Initial temp of water 22.3°C Initial temp. of hot metal 98°C Maximum temp of water 23.27°C Change in temp of water 0.97°C Change in temp of metal -65.5°C Final temp. of metal 32.5°C Recorded water Temp in T = x seconds T = 15 seconds 22°C T = 30 seconds 22.5°C T = 60 seconds 22.5°C T = 90 seconds 23°C T = 120 seconds 23°C T = 150 seconds 23.5°C T = 180 seconds 23.5°C T = 210 seconds 24°C T = 240 seconds 24°C T = 270 seconds 24°C T = 300 seconds 24°C Specific Heat of Sand Trial One Trial Two Mass of test tube 56.93 g 53.93 g Mass of sand and test tube 106.94 g 103.97g Mass of sand 50.01 g 50.04 g Volume of water 100 mL 100 mL Mass of water 100 g 100 g Initial temp of water 22°C 22°C Initial temp. of hot sand 98°C 98°C Max. temp. of water 28.45°C 30.09°C Change in temp. of water 6.45°C 8.09°C Change in temp of sand -66.31°C -88.68°C Recorded water Temp in T = x seconds Trial One Trial Two T = 15 sec 30°C 34°C T = 30 sec 30°C 32°C T = 60 sec 30°C 30.5°C T = 90 sec 30°C 30.5°C T = 120 sec 30°C 30°C T = 150 sec 28°C 29.5°C T = 180 sec 28°C 29°C T = 210 sec 27.5°C 29°C T = 240 sec 27°C 29°C T = 270 sec 26.5°C 29°C T = 300 sec 26°C 28.5°C Equations and Sample Calculations The relations between temperature change and heat lost by the water and gained by the metal / sand can be written separately as: (1) where and are the specific heats of water and sand, respectively. By assumption, the heat gained by the sand equals the heat lost by the water: (2) Substituting Eqs.(1) into Eq.(2) to eliminate the heat gain/loss terms gives: (3) The assumption that the sand and water end up at the same temperature can be written as: (4) Substituting Eq.(4) into Eq.(3) gives: (5) We have measured or otherwise know everything in Eq.(5) except , so we can solve for it: (6) Sample Calculations: max. equilibrium temp. of water (metal) = [ 22 + (2)(22.5) + (2)(23) + (2)(23.5) + (4)(24) ] / 11 = 23.27°C specific heat (lead) = [ -(4.18 J/g-°C)*(100 g)*(0.97°C) ] / (50 g)*(-65.5°C) = 0.124 J/g-°C percent error = |literature value - experimental value| / literature value * 100% = (0.128 J/g-°C - 0.124 J/g-°C) / 0.128 J/g-°C * 100% = 3.125% max. equilibrium temp. of water (sand – first trial) = [ (5)(30) + (2)(28) + 27.5 + 27 + 26.5 + 26 ] / 11 = 28.45°C specific heat (sand – first trial) = [ -(4.18 J/g-°C)*(100 g)*(6.45°C) ] / (50.01 g)*(-66.31°C) = 0.813 J/g-°C percent error = |0.795 J/g-°C - 0.813 J/g-°C| / 0.795 J/g-°C * 100% = 2.264% Discussion / Observations Assuming that no other heat was lost from or accumulated into the system (calorimeter), energy balance calculations merely involved the quantities of all substances present and the corresponding change in temperature when water was separately mixed with the lead and the sand. It was observed that as the hot metal, initially at 98°C, was transferred into the calorimeter with water at 22.3°C, it cooled to a temperature of 32.5°C. The same behavior was noted for the two trials performed for sand where significant temperature changes of -66.31°C and -88.68°C had been recorded within 5 minutes of allowing water to arrive at the maximum equilibrium temperature. As expected, it increased in temperature as such process enabled the heated solid materials to release energy to be absorbed by the water upon the stirred mixture stage. Since measurements were done using thermometer, most likely the unnoticed defect in thermometer could have brought about significant error. We might have also imparted error through inaccurate reading or inappropriate use of the timing device whereas invisible errors which occurred by nature may have come from unnecessary losses in heat from the system. Evidence / Results Specific Heat of Lead = 0.124 J/g-°C % error (deviation from literature value) = 3.125% Specific Heat of Sand (Trial 1) = 0.813 J/g-°C % error (deviation from literature value) = 2.264% Specific Heat of Sand (Trial 2) = 0.762 J/g-°C % error (deviation from literature value) = 4.151% Conclusion Because the calorimeter used was merely a basic setup, unaccounted heat loss / accumulation via other factors might have chiefly affected experimental results. It bore reflection on the degree that the obtained specific heat values in the experiment deviated from the accepted value. The same procedural steps may be carried out on determining specific heats of substances other than lead and sand. Each experimenter, however, should seek the necessity of being extra-careful in the delicate process of monitoring temperature change, ensuring as well that all measuring apparatuses / devices undergo thorough calibration prior to use so that high accuracy may be achieved. References Chapter 2: The First Law of Thermodynamics (UCLA). “Thermochemistry Experiments.” Retrieved from http://eduframe.net/andc/chemistry/Che03/Che03-Neeti/odlcodethermoneeti.htm. Read More