Module Code: FC021

Class/Group: A

Module Title: Physical Sciences

Assessment Title: Lap Report

Assignment Title: Specific Heat Capacity Experiment.

Abstract

This experiment was divided into 2 parts; first it obtained the SHC of water by monitoring the temperature change, and secondly it  investigated the specific  heat capacity of copper. A kettle was used to heat 1kg of water and the temperature was recorded with a thermometer at 15 second intervals. The time was then used to calculate the energy supplied from the power rating of kettle, and was plotted on to a graph. The SHC of water was evaluated from the gradient of the graph divided by 1kg. Time was taken using a stopwatch for 22 laps; every 15 seconds. This was repeated for a total of 3 trials. The maximum temperature achieved after each trial were 102.4℃, 101.9℃ and 103.4℃ . Overall, the specific heat capacity of water was calculated to be 5.3KJ/(℃Kg)  ± 1.2KJ/(℃Kg).  Using this value, the SHC of copper was then determined to be 323J/(℃kg)  ± 88.2J/(℃kg)  by  suspending a 100℃-copper bar in a beaker  of  water  and  monitoring  the  temperature  over  time.  The  %  differences  of  the experimental values in comparison to the theoretical is 24.8% for SHC of water and 17.2% for SHC of copper.

1. Introduction

An investigation was carried out to monitor the temperature change of water in its standard state as it is heated by akettle overtime, and then a hot bar of copper was placed in a beaker of cold water and the temperature was recorded overtime. The study of this experiment was aimed to obtain an estimated experimental value of the SHC of water and copper.

It is known according to the Scottish Scientist, Joseph Black who first found that different substances of equal mass required different amounts of heat to cause a temperature rise of the same amount; which stimulated the concept of specific heat (Britannica, 2014). The heat capacity of an object is the amount of heat added to an object divided by its increase in temperature. It can be calculated using equation 1 below (Walker, 2014).

Where: C = Heat capacity (JK-1  or J°C-1)

             Q = Heat energy (J)

ΔT = Change in Temperature (Kor °C)

If a system is gaining heat then Q is considered to be positive as well as the change  in temperature. If a system is losing heat then Q is considered to be negative and so is the change in temperature.

Heat is the energy transferred between objects as a result of a temperature difference. Heat flows between objects when they are in thermal contact. Once the transfer of heat between two objects placed in thermal contact stops they are considered to be in thermal equilibrium. Heat is a scalar quantity and it is a form of energy so it is measured in Joules.

The temperature rise during heat transfer across objects depends on several factors such as; the  mass  of  the  object,  the  amount  of  energy  transferred  to  the  object  itself  and  the substance the object is made out of.

The heat capacity of an object varies depending on its particular mass, the quantity used to describe this is called specific heat capacity. To calculate the specific heat capacity, the total energy of the system is considered to be conserved. It can be calculated using equation 2 (Walker, 2014)

Where: C = Specific Heat capacity (JK-1Kg-1  or J°C-1Kg-1)

Q = Heat energy (J) m = Mass (Kg)

ΔT = Change in Temperature (Kor °C)

Therefore, by definition the SHC of a substance is the amount of energy required to change the temperature of 1kg of the substance by 1°C. A substance with a high specific heat capacity is useful for storing heat energy.

2. Materials and Method

2.1 Equipment and Materials:

●   Electrical Thermometer

●   Electronic Mass Balance

●   Beaker

●   Timer

●   Electric Kettle (1850 - 2200W)

●   Gloves

●   Goggles

●   String

●   Calculator

●   Power Supply Cable

●   Water Source

●   Pen

●   Copper bar

●   Insulating foam

Figure 1: Original illustration of materials set up for part 1 of the experiment to estimate SHC of water.

Figure 2: Original illustration of materials set up for part 2 of the experiment to measure masses.

Figure 3: Original illustration of materials set up for part 2 of the experiment while boiling copper bar.

Figure 4: Original illustration of materials set up for the final steps of part 2 of the experiment.

2.2 Method:

Part 1: Monitoring the temperature change to obtain the specific heat capacity of water.

In this first part of the experiment the temperature change was recorded simultaneously as the kettle continued to boil with constant corresponding time intervals; to finally evaluate a graph and investigate the properties of water. The equipment was set up along a desk as shown in figure 1, this was done as follows:

First the stopwatch was reset to zero, and the kettle was plugged into a power source socket. Next, using an electronic mass balance the mass of an empty beaker was measured. Then the beaker was filled to measure out 1 kilogram of water taking into consideration the mass of the beaker as well. The water in the beaker is then poured into the kettle. After that step, the probe of the electric thermometer was placed inside the kettle so that it measured the water temperature and not the heating element of the kettle. The initial temperature of the water was noted before the kettle was switched on.

Before switching the kettle on, as safety precautions goggles were worn as eye protection and insulated gloves were put on as hand protection. Once that was completed, the kettle was switched on and it began to boil while the timer was started simultaneously at the same time. Finally, the temperature of the water was recorded according to the reading on the digital thermometer at 15 second intervals. This procedure was continued for a total of 24 laps of each interval.

For extra certainty, the mass of the water was measured on the electric balance 3 times to ensure it’s as accurate as possible. The average reaction time was estimated by carrying out an online reaction time test on the website “human benchmark” (Human Benchmark, 2007). This reaction time test was repeated 3 times and the average value was used.

Part  2:  Monitoring  temperature  to  calculate  the  specific heat capacity of copper.

In this second part of the experiment the temperature change was recorded simultaneously as the copper  bar was held in a beaker of cold water with constant corresponding time intervals; to finally evaluate an estimated value for the specific heat capacity of copper. The equipment was setup along a desk as shown in figures 2, 3 and 4, this was done as follows:

The first step was carried out as show in figure 2. The mass of the copper bar was measured on a mass balance. Next, the mass of an empty beaker was recorded. After that, 200gof water was measured out in the beaker using the mass balance. Note that the mass of the beaker itself was taken in to consideration when reading the balance scales as it was not a part of the 200g of water.

In addition, a kettle was then filled just over halfway with water. A string was attached on to the copper bar as it was suspended in the kettle. However, it was ensured that the copper bar did not make any contact with the kettle’s heating element. The kettle was then switched on, and it began to boil. While the kettle was boiling as shown on figure 3, the beaker with 200g of cold water was placed on a block of insulating foam. Using a thermometer, the initial temperature of this cold water was recorded.

Once the kettle has finished boiling, the copper is now assumed to be at a temperature of 100°C, the string that  has  suspended the copper  bar was  pulled to  carefully  remove the copper bar. As a precaution, the copper bar itself was not touched by bare hands as it was very hot. Before carrying out the nextstep, the timer was reset to zero. Next as presented in figure 4, the copper bar was suspended in the beaker of cold water, and it was ensured that is did not touch the sides of the beaker or rest at the bottom of the beaker. A thermometer was held in the water in such position that it did not touch the beaker or the copper bar. Finally, the temperature of the water was measured every 15 seconds using a timer as the temperature began to settle.

3. Results

Part 1: Monitoring the temperature change to obtain the specific heat capacity of water.

The repeated measurements of temperature from each trial were used to evaluate the average temperature, for every 15 second interval. The temperature was noted for a total of 22 laps. The obtained experimental values are shown below in table 1 and table 2,which are coordinated to their corresponding graphs 1, and 2. Furthermore, their uncertainties were calculated for each recorded result.

The uncertainty for cumulative time in table 1 and 2 were calculated using equation 3, and the uncertainty for average temperature was calculated using equation 4.

The energy values in table 2 were calculated using equation 5. Where the average power rating of the kettle was 2025W.

Graph 1 begins with a constant steep positive gradient from 0s up until 180s as the kettle is in the process of heating up. The kettle begins to boil at  180s, and reaches its maximum temperature of 103.6°C at 195s. While the kettle is boiling the gradient is zero as the graph displays a flat straight line. In this case, adding heat no longer increases the temperature. This is because when energy is added to any liquid substance at the boiling temperature, the liquid is converted to a gas at this point. Therefore, the energy being added to the liquid is being used to break the bonds between the liquid molecules without causing a temperature change. The change of state process is what consumes the energy rather than the  temperature increasing.

Graph 2 was plotted using the amount of energy transferred into the kettle for a period of 315s. The dotted line represents the trend line which shows an average of the plotted values. Once the kettle began boiling the energy transferred remained constant as shown in graph 2; the gradient at this point was zero and the graph was a flat straight line.

The significance of the gradient of this graph represents the change in energy divided by change in temperature. Although temperature is the dependent variable that belongs on the y-axis and energy is the independent variable that belongs on the x-axis, in graph 2 the axis’s have been swapped as this arrangement allows us to find the heat capacity value from the gradient. The mass of water involved in this process was 1kg, therefore the gradient can be divided by the mass to obtain an estimated value for the specific heat capacity of the water.

The red dashed line represents the most appropriate region to calculate an estimated value for the gradient using equation 6, and the SHC is found using equation 2.

Therefore, the experimental value obtained for the specific heat capacity of water was 5.3 KJ/Kg℃

Part  2:  Monitoring  temperature  to  calculate  the specific heat  capacity of copper.

As the copper bar was suspended into the beaker of cold water in part 2 of the experiment, a timer was then used to measure the temperature change of the water in the beaker that is surrounding the copper bar at 15 second intervals. The values are shown in table 3 above. The temperature stopped changing after 225s and it remained constant at 26.0℃ .

The energy absorbed by the water is equal to the energy of the copper bar itself. Therefore, the energy absorbed by the water was calculated using the experimental value for the SHC of water as:

From this value, the SHC of copper was determined to be:

Therefore, the water in the beaker is gaining energy and the copper bar is losing energy as it is placed in the water so the sum of heat transfers can be described as: