Thermal Equilibrium Experiment free essay sample

This laboratory focused on the thermodynamic processes involved when two incompressible substances are mixed together. 12 experiments were performed, 10 involving the combination of a measured amount of hot and cold water and 2 involving the combination of ice and liquid water, the majority of these experiments were performed three times. The average variance in final temperature for each experiment was less than 10 percent providing proof of repeatability. Equipment used during the experiment included a gram scale, thermocouple, Styrofoam cup, glass beakers, microwave, an ice bath and ice. The first half of the experiment was dedicated to the mixing of two containers of water at different temperatures. The mass of the water in each container was measured and the containers were then heated or cooled to achieve the temperature desired for the experiment. The temperature was measured with a thermocouple before and after mixing. The data was recorded and is included in tables. The second half of the experiment involves the mixing of ice and liquid water. Water was weighed and cooled then mixed with an amount of ice that was also weighed. The temperature before and after mixing was recorded and included in tables. When the experiments were completed analysis was performed using the laws of thermodynamics. The data collected was used in equations to find theoretical values for final equilibrium temperature. The theoretical values were compared with those measured during the experiment. The total average percent difference between the measured final temperature and the theoretical final temperature is less than 5. 0%. This low deflection between measurement and theory lends credibility to the experiment and proof of the concepts provided within the experiment. When two incompressible substances of different temperatures are combined, there will be a resultant equilibrium temperature that lies between the temperatures of the substances that were combined. The mass of the substances greatly affects the resulting final temperature. An incompressible substance is one whose volume can be considered constant no matter the change in pressure. In this laboratory, the incompressible substance water was used in its liquid and solid states. The First Law of Thermodynamics is essentially an energy balance equation and is state below. Q – W = ? U (Eq. 1) Q represents the amount of heat transferred into or out of the system. W represents the amount of work done by or on a system. ?U represents the change in the internal energy of the system. The units for Q, W and U are kilojoules. When analyzing a thermodynamic process, a system boundary must be established. Establishing the boundary will determine how complicated or simple the first law analysis is. The boundary for this experiment was established in such a way that there was no heat transferred into or out of the system. There was also no work being done on or by the system. A value for work would be required if a device such as a compressor or turbine was included in the system. Since there is no heat transfer across the boundary or work done, the Q and W values are considered to be zero. The equation now becomes. 0 = ? U = Ut2 – Ut1(Eq. 2) In order to use equation 2, the mass and specific heat of the incompressible material was determined. Specific heat refers to the amount of energy, measured in kilojoules, required to raise one kilogram of the incompressible substance by one degree Kelvin or Celsius. The specific heat value for water at 1 atmosphere of pressure varies according to temperature, but the average is 4. 18 KJ / KG* ? K Using mass and specific heat values, the following equation for the change in internal energy was used to calculate final equilibrium temperature. 0 = [ M * C * ( T2 – T1 ) ]substance 1 + [ M * C * ( T2 – T1 ) ]substance 2(Eq. 3) M represents the mass of the substance ( KG ) C represents the specific heat of the substance ( KJ / KG * ? K ) T2 represents the final equilibrium temperature ( ? Kelvin ) T1 represents the initial temperature ( ? Kelvin ) Modifications to this equation must be made in the case of phase change. Phase change occurs when a substance changes from a solid to a liquid for example. When hot water was mixed with ice, the ice changed phase from solid to liquid. This phase change must be taken into account because a portion of the total system energy is committed to the process of turning the solid ice into liquid water. To accomplish this, the latent heat of melting for ice is included in the energy balance equation. The average percent difference between theoretical final temperature and measured final temperature for Table V is 5. 23%. This indicates that the theoretical calculations and the measured values for final temperature are close enough to one another to lend credibility to the experiment. Data from Table IV was used in Equation 4 to find the theoretical final equilibrium temperatures for the experiments involving the mixing of ice and water. The average percent difference between the theoretical final temperature and the measured final temperature is 3. 61%. This is also an indication of a legitimate, repeatable experiment. Possible sources for error in the experiment contributing to variations between measured and theoretical final temperatures are listed below. †¢Liquid residue remaining in transfer beakers causing the mass of the water that was actually mixed to be lower than that measured in the beaker before mixing. †¢Evaporation of liquid from the hot water beaker during transfer from the microwave to the laboratory station where the experiment was being performed. This will also cause a lower mass of water to be mixed. †¢Accuracy of testing equipment. The thermocouples and gram scales used have tolerances above and below actual values being measured. †¢Heat transfer due to the environment such as convection and radiant heat transfer. Though our experiment was simplified by specifying a system boundary by which there was no heat transfer into or out of the system. The fact that some amount of heat transfer due to the environment occurred can’t be completely ignored. The Equilibrium Experiment provided valuable information concerning the thermodynamic processes involved in the mixing of two incompressible substances. Data was successfully obtained from numerous experiments and analyzed using Equations 3 and 4. The overall percentage difference from data collected to theoretical calculations made is a mere 4. 42%. The quality of the results lends credibility to the experiment and confirms established theory. When two substances of different temperatures are combined, they will eventually reach an equilibrium temperature that lies between the initial temperatures of the two substances. The mass and temperature of the objects govern what the final temperature will be.