Experiment 2 - Methods Of Mixtures 2w3l11

Experiment 2: Method of Mixtures Laboratory Report Byron Leander Tan, Chelsea Leigh Tan, Kyle Gabriel Tanchuling, Ma. Agatha Beatrice Uson, Angelica Uy, Louise Erika Vargas Department of Math and Physics College of Science, University of Santo Tomas España, Manila Philippines

Abstract There were two activities done in the experiment namely, specific heat of metal and heat of fusion of water. Results in this experiment showed that the heat lost in the system is equal to the heat gained in the system; furthermore, this concept enabled the group to determine the specific heat of the metal object as well as the latent heat of fusion of water. I. Introduction In this experiment, the specific heat of a solid was determined by the method of mixtures; the latent heat of fusion and heat of vaporization of water were determined. Phase changes occur when heat is added at a constant rate until physical alterations happen to the substance. Specific heat of a solid substance can be determined by the "Method of Mixture" using the concept of the "Law of Heat Exchange". The method of mixture based on the fact that when a hot substance is mixed with a cold substance, the hot body loses heat and the cold body absorbs heat until thermal equilibrium is attained. At equilibrium, final temperature of mixture is measured. The specific heat of the substance is calculated with the help of the law of heat

exchange. A method of determining the heat of fusion of a substance whose specific heat is known, in which a known amount of the solid is combined with a known amount of the liquid in a calorimeter, and the decrease in the liquid temperature during melting of the solid is measured. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature. The energy required to change a gram of a substance from the solid to the liquid state without changing its temperature is commonly called its "heat of fusion". This energy breaks down the solid bonds, but leaves a significant amount of energy associated with the intermolecular forces of the liquid state. The energy required to change a gram of a liquid into the gaseous state at the boiling point is called the "heat of vaporization". This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas. For an ideal gas, there is no longer any potential energy 1|GROUP 10

associated with intermolecular forces. So the internal energy is entirely in the molecular kinetic energy. In this experiment, students are expected to  Determine the specific heat of a solid by method of mixtures  Determine the latent heat of fusion and heat of vaporization of water. II. Theory This experiment involves specific heat, and method of mixture. Specific heat of a substance is the number of calories needed to rise the temperature of one gram of substance, one degree centigrade. In order to determine the specific heat of an object, the method of mixture is performed. In the method of mixture, the law of heat exchange is used. The basis of the method of mixture is when a hot substance is combined together with a cold substance; the hot body undergoes an exothermic effect in contrast with the cold body experiencing endothermic effect until thermal equilibrium is attained. Once equilibrium is reached, the final temperature is measured. The specific heat of the substance is then calculated using the formula: C1 = M1C1 (T-T1) + mccc (T-TS) / MS (TS-T) Where MS is the mass of the substance, ml mass of the liquid, mC is the mass of the calorimeter, TS as the initial temperature of the substance, T1 as the initial temperature of the liquid, TC as the initial temperature of the calorimeter, CS as the specific heat of the

substance, C1 as the liquid’s specific heat, CC as the calorimeter’s specific heat, and T as the final temperature of the mixture. III.Methodology The activity done was activity 2. The inner vessel of the calorimeter was weighed, and was filled with half full of water afterwards and weighed again to get the mass of water. The inner vessel was placed into its insulating jacket. The initial temperature of water inside the calorimeter was recorded. Pieces of ice were dried and added to the water inside the calorimeter carefully. The mixture was continuously stirred until all the ice has melted and thermal equilibrium was established. The temperature at thermal equilibrium was recorded. The inner vessel was weighed once again and the heat of fusion was then computed by Conservation of Heat energy. And lastly the % error was obtained. IV. Results and Discussion Mass of Inner vessel of calorimeter Mass of Inner vessel of calorimeter with water Mass of water inside inner vessel of calorimeter Mass of Inner vessel of calorimeter, water and melted ice Mass of melted ice Initial temperature of water and inner vessel of calorimeter Equilibrium temperature of inner vessel of calorimeter, water and melted ice Calculated latent heat of

42.24g 182.74g 135.5g 213.31g

30.57g 25.5⁰C 7⁰C

406.00

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fusion

J/g

Accepted value of latent heat 333.55 of fusion J/g

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%Error

17.84%

The results of the experiment were as follows:

VI. Applications 1. Is   it   possible   to   add   heat   to   a   body without changing its temperature? ­

The initial temperature of the water and inner vessel of the calorimeter was 25.5⁰C at room temperature. The equilibrium temperature of the inner vessel of the calorimeter, water and melted ice was 7⁰C, this was the constant temperature after the ice had melted into the water and stirred with the thermometer for about 3 minutes. This change in temperature from 25.5⁰C because the heat energy coming from the room temperature water will have gone to the ice to melt it and mix with the room temperature water. The energy will keep flowing until all the ice has melted into the water / all of the water has the same temperature. The calculated latent heat of fusion was 406.00 J/g with a %Error of 17.84%, this is probably because some of the heat escaped the calorimeter to the room temp. air in the room or, the ice did not start at a room temperature of 0⁰C V. Conclusion The specific heat of the metal and the latent heat of fusion has been determined through calculating it. The specific heat of the metal was determined through the method of mixtures. The latent heat of fusion is known to be at 406.00 J/g°C, not too far from the accepted value which is 333.55 J/g°C.

Yes, it is possible, you can add heat to a body without changing its temperature, while a substance is undergoing a phase transition,   its   temperature   does   not change. In this circumstance, the rate at which we increase heat to the substance determines the rate at which the phase transition occurs. Like a boiling water: adding   heat   will   only   result   to   phase change but not to its temperature.

2. Is   the   value   heat   of   vaporization constant? ­

No, the heat of vaporization correspond to the heat that the liquid lost when the molecules phase distorted. Thus heat is reliant on temperature

3. Explain   why   steam   burns   are   more painful than boiling water burns ­

Steam causes   a crueler burn due   to   the high   latent   heat   of   evaporation   (latent heat   is   the   energy   essential   to convert water into steam

4. Early   in   the   morning   when   the   sand   in the beach is already hot, the water is still cold. But at night, the sand is cold while the water is still warm. Why? ­

Water has high specific heat capacity. it takes   slower   rate   to   absorb   or   release heat   compared   to   the   sand   which   has lower heat capacity causing the sand to absorb and release at a faster rate. 

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5. Why   is   an   alcohol   rub   effective   in reducing fever? ­

This   is   because   alcohol   reduces   a person’s body temperature. Latent heat of vaporization of alcohol is much lower than   water   so   that   alcohol   evaporates faster at lower temperatures.

6. Why is water usually used as a coolant? ­

Water   is   commonly   used   as   a   coolant since   it   has   a   high   capacity,   has   the highest   specific   heat   of   any   common substance, 1 calorie/gm °C = 4.186 J/gm °C,   which   makes   it   suitable   as   a   heat transfer   medium.   The   high   heat   of vaporization   of   water   makes   it   an effective coolant for the human body via evaporation   of   perspiration,   extending the   range   of   temperatures   in   which humans can subsist.

7. How much heat is needed to change 1g of ice at 0°C to steam at 100°C? ­

m=1g Q=m* ΔHvaporization =(1g)(540 cal/g)= 540cal ΔHvaporization=540cal/g

Find the resulting temperature when 60g of copper at 100  °C is placed inside the calorimeter.

­

T=0.06x385 (100 ­ t) =( 0.15x900 + 0.25x4200) ( t – 30)= 31.3458 C.

References [1] HyperPhysics. Heat of Fusion. Retrieved February 7, 2017 from http://hyperphysics.phyastr.gsu.edu/hbase/thermo/phase2.html [2] HyperPhysics. Specific Heat. Retrieved February 7, 2017 from http://hyperphysics.phyastr.gsu.edu/hbase/thermo/spht.html [3] City Collegiate. Specific Heat. Retrieved February 7, 2017 from http://www.citycollegiate.com/specific_heat. htm [4] Practical Physics. Method of Mixtures. Retrieved February 7, 2017 from http://www.vias.org/glazebrook_practphys/ wrapnt75A18C_the_method_of_mixture.ht ml

8. An aluminum calorimeter has a mass of 150g and contains 250g of water at 30 °C.

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