Latent Heat and Specific Heat Capacity

Part A – Latent Heat

AIM

To measure the Latent heat of fusion of ice.

Introduction

When energy is applied to a substance in the form of heat, a change in temperature is generally perceived to occur. The applied heat, Q, which forces a change in temperature, , is found by: [pic 2][pic 1]

[pic 3]

Where  is the specific heat of the substance and  is the mass of the substance. [pic 4][pic 5]

However there exist situations where heat applied to a substance does not cause a change in temperature rather a change in phase. The most common changes in phase are from solid to liquid and from liquid to gas. The transformational heat or the heat of transformation is the amount of heat needed to complete a phase change. More specifically, this heat can be referred to as the heat of fusion when dealing with a phase change from a solid to a liquid. The amount of energy, Q, required to accomplish this phase change can be found by:[pic 6]

[pic 7]

Where  is the mass of the substance and  is the Latent heat of the substance.[pic 8][pic 9]

During a complex heat exchange between a solid and a liquid, i.e. ice and water, the solid firstly absorbs heat from the liquid and increases its own temperature to melting point. The solid then undergoes a change in phase and becomes a liquid. The heat needed to complete this process, a phase change, is known as the Latent heat of the substance. More specifically, the latent heat of fusion of a substance is a measure of the heat per unit mass that is needed to complete a phase change from a solid to a liquid without the temperature of the substance changing. The latent heat of a substance can be found by:[pic 10]

[pic 11]

[pic 12][pic 13][pic 14][pic 15][pic 16][pic 17][pic 18]

Experimental Method

1. The Calorimeter, Stirrer and Lid were weighed together and there total mass recorded. The calorimeter was filled half-way with water and weighed again. The masses were subtracted to find the mass of the water.
2. The starting temperature of the water was recorded and the ice cubes were taken out of the freezer and dried.[pic 19]
3. The ice cubes were placed into the calorimeter. The temperature of the water was then recorded every 30 seconds for 3 minutes. The water was continuously stirred over the 3 minutes.
4. After the ice had fully melted the calorimeter was weighed again and the mass recorded. This mass was subtracted from the mass of the calorimeter with water and the total mass of the ice was recorded. [pic 20]
5. The Latent heat of fusion of the ice was then calculated by using Equation 3 (see above).

Results

Table 1: Fusion of Ice

[pic 21][pic 22]

Table 2: Mass of Equipment

Data Analysis

[pic 23][pic 24][pic 25][pic 26]

Experimental Discussion

Experimental Question: If the ice was not dry, how would the result for the latent heat, , be affected?[pic 27]

Ice is defined as being the solid state of water. The change in phase from water to ice occurs when water is brought below a temperature of 0°C. Therefore water can only remain a solid when its temperature is less than 0°C. When ice is transported into an environment that is above 0°C it almost instantly begins a phase change into water. This water gathers on the outside of the ice and has a temperature of 0°C. If this water is added to water at room temperature, i.e. ice cube not dried, then it will increase the total volume of water without gaining the amount of heat that the ice would gain. Less ice means that the original temperature of the water will not drop as far as expected, resulting in the final temperature to be too high. This ultimately produces an experimental value of the Latent Heat of fusion of ice that is considered to be too low.

The final result achieved for the Latent Heat of Fusion of ice in this experiment confirms that indeed this experiment was a success. The widely accept value of the Latent Heat of Fusion of ice is considered to be about . The value that was achieved in this experiment was . Although the difference may be in the tens of thousands, the numbers themselves are in the hundreds of thousands thus producing a deviation of about only 3.9%. Considering the limitations of some of the resources that can affect the reliability of the calculations this result is actually rather impressive. [pic 28][pic 29]