Comparison of Specific Heat Capacity of Different Metals

Samerah Mansha

Aim

The aim of this investigation was to measure the specific heat capacity (SHC) of various different metals such as aluminum, iron and brass of different volumes to find out if they all have the same SHC or different.

Additionally, insulation was used to measure how efficient insulation was against heat loss.

Hypothesis

Previous research in background information states that there should be a difference between the SHC of aluminum, brass and iron.

Null Hypothesis

There will be no difference between the SHC of aluminum, iron and brass.

Prediction

The SHC of aluminum will be higher than iron and copper, this is because the volume the less dense the meta lis, thus the higher the SHC because the metals contains big atoms which slowly heat up thus more energy is needed to make the molecules get hot and move around. Insulation will also make a difference by conserving the heat energy, which will give more accurate results as more heat will most likely be conserved and not lost.

Background information:

Thermal energy is the amount of energy of a substance or system which is associated to its temperature. Heatandtemperatureare both related with thermal energy but differ. Heat is the transmission of thermal energy from one object to another due to temperature differences between them.Heat is the total energy of all the molecule motion within the object and is measure in joules. Whereas temperature is a measure of degree of hotness of an object, i.e.how hot or cold,therefore it’s a measure of average thermal energy of molecules within substance and measured in degrees Celsius.

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Temperature can be measured via the Celsius and Kelvin scales. The Celsius scale is built upon two fixed points, the freezing mark at 0°C and boiling point at 100°C, whereas Kelvin scale is based on absolute zero at -273 where particles have minimum energy. The Celsius scale has degrees the same size as Kelvin,but Kelvin scale starts 273 lower than Celsius absolute zero scale, for example 0 °C is 273 degrees.

When heat energy is transferred to an object, its temperature increase is dependent upon, the mass of object, the material the object is made from and lastly the amount of energy transferred to object. The more heat energy transferred to object results in a more temperature increase.

The SHC of a substance is known as the amount of energy needed to change the temperature of 1kg of substance by 1°C. Different substances have different SHC e.g. water, oxygen and metals. Water has a high SHC of 4200 j/kg°C, School Physics, 2013.

This therefore makes water suitable for storing heat energy which is efficiently useful for transporting it around home via heating pipes.

Metals are good conductors of heat, yet non-metals are usually poor conductors of heat which are called insulators. Heat energy is simply conducted from hot end of object towards the cold end and the electrons within metal leave their atoms therefore move around within the metal as free electrons. The metal atoms which are left behind are known as charged metal ions.These ions are placed carefully together whilst vibrating constantly.The hotter the metal becomes, it results in the the vibrations gaining more kinetic energy. As a result, this kinetic energy gets transferred from hot parts of metal towards cooler parts via free electrons.These free electrons then move throughout the metal, each colliding with many ions transferring heat energy as they go along.

Metals with a high SHC take a lot of heat energy and take a long time to heat up and cool down.

Heat can be transferred via conduction, convection and radiation.Conduction is thermal energy transfer which occurs in solids that are in contact with each other, causing particles to gain energy and vibrate, passing on heat energy to nearby particles, resulting in rise of temperature at other side. Convection is another type of thermal energy transfer which occurs in liquids and gases where particles freely move. Particles with kinetic energy move from hotter regions to cooler regions, transferring thermal energy. Radiation is known as heat transfer that doesn’t need contact between heat source and heated object,due to heat having the potential to be transmitted via empty space by thermal radiation.

Heat can also be stored in the form of insulation. Insulation prevents or reduces heat from escaping an object by providing a barrier between areas that are significantly different in temperature.

Materials

• 12v immersion heater of 50w power
• Block of aluminum, iron and brass with a hole in the middle
• Wires
• 6V power Supply
• Ammeter
• Stop Clock
• Top Pan Balance
• Thermometers
• Insulation
• Stop watch
• Ruler
• Insulating material

Method:

• Firstly all the metal blocks were weighed via a top pan balance
• The metal blocks were then measured via a ruler for their length and diameter.
• The thermometer was put into each of small whole in the metal blocks so that the initial temperature could be measured.

Figures1: Measuring the initial temperature of the metal blocks.

• The immersion heater was connected up to a 6V voltmeter and ammeter via wires.
• The 6v power supply and was switched on until the immersion heater was warm.

• The immersion heater was put into the large hole in the metal blocks and the stop clock was started. After 10 minute the power supply was switched off and the temperature of the block was measured and recorded.

This method and chosen measurements were chosen as previous research using a similar method gained successful results via this method; therefore to improve reliability a similar method was used.

As heat was lost during the practical, a modification was made order to prevent heat loss, which involved the same experiment to be repeated in the same way but this time the metals were surrounded with insulation material to reduce the amount of heat loss and would result in more reliable results.

Figures: Aluminum, brass and iron wrapped up in insulating material.

Safety

The immersion heaters were checked before use; any that were faulty were rejected and replaced. Heat resistant gloves were worn when handling the immersion heater and the heated up metals to preventing any burns. The wires were also checked thoroughly to see any defaults. Additionally, the power supply was made sure it was turned off when not in use to prevent any electrocution.

Results

Table: 1 Measurements of the metals

Table: 2 Results of the non-insulated metals.

Due to heat being lost to the environment, an insulating material was wrapped around the blocks

Table: 3 Results of the insulated metals.

Analysis

Equation for SHC = E = m × c × θ

Heat energy (E) = Mass kg (m) x SHC J/g°C (C) x Temperature change°C (θ)

Table:4 SHC calculations of the non-insulating metals

Table:4 SHC calculations of SHC of insulating metals showing more accurate results which will be used throughout the discussion and conclusion.

Graph:1 Graph showing the comparison of SHC results of metals with and without insulation.

Observations

The results of the insulated aluminum showed the highest SHC, as aluminum takes 0.121J of heat to raise 1 gram by 1°C.With the least SHC being the insulated iron needed 0.055J of heat to raise 1 gram of the given metal by1°C.

The results showed that insulated metals showed an overall increase of SHC of the metals, thus more accurate as more heat is conserved and is not much heat would be lost to the environment.

The metals without the insulation showed a lower SHC due to heat being lost to the environment, thus are less accurate.

Discussion

Research states that the accepted value for SHC of aluminum is 0.903J/g°C,therefore it would seem that my result of 0.121J/g°C is not accurate, when errors are taken into account.

The accepted value for SHC of brass is 0.380/g°C and the result achieved within the experiment was 0.055/g°C which was again quiet far off.

The accepted value for the SHC of iron is 0.44/g°C and the result achieved from the experiment was 0.051/g°C.

Graph:3 Comparison of results of SHC from this experiment and actual published SHC.

The published values of SHC show that iron has a higher SHC than brass, but within my experiment brass has a slightly higher SHC value than iron.

Overall the results achieved

from this experiment are quiet significantly lower than the actual SHC values for the given metals. This therefore shows that even with insulation a lot of heat was still lost from the metals.

Conclusion

Regardless of the SHC results not being as accurate as the published results, the hypotheses and prediction was proven correct and were fully supported by the evidence of the results achieved within this experiment, as each metal had a different SHC value thus showing variation. This is due to the metals having different volumes. It was also predicted that aluminum would have a higher SHC than iron and brass, which was proven correct as aluminum had a larger volume thus less dense so it would need an higher SHC because more energy is needed to heat up

SHC is therefore affected by the volume of a metal, as the atoms and molecules found within the metal are packed differently thus heat up at different rates,

Evaluation

As the SHC results achieved were not as accurate to the published SHC values, this may due to limitations which may have been present within the experiment such as the first being the accuracy of the measuring thermometers which only allowed one to measure in whole degrees and has an a error of 0.05°C. To overcome this limitation a digital thermometer which is more exact could have been used to achieve more accurate readings.

It was also quiet difficult to keep the current constant which would have affected the SHC as different flow of current allows a different flow of electrons to transfer to flow of heat energy, thus a resistor could have been used to control it.

Another limitation could have been because it was difficult to get all the results at the same time, i.e. the temperature and current at correct time, using a scientific computer to measure the variables would remove any human errors with reaction times when measuring time and this would achieve temperate reading within few milliseconds.

The results showed that even no insulation on metals heat was still lost thus couldn’t achieve an accurate SHC values. Regardless of having insulation heat was still lost which could have been the reason for the inaccuracy.

Additionally another limitation could have been that the insulating material used was all different for each metal, thus showing that different. This effects the results as different insulation materials have different properties, thus reducing reliability as not all materials could have been useful in conserving heat energy.

On the other hand, the use of electrical balance to measure the masses of the metals within experiment avoided any uncertainties and errors related to the mass value, thus increasing reliability of data to some extent.

Overall to improve reliability the experiment could have been repeated four times to obtain average SHC results leading to more accurate results, thus helping to reduce random errors.

References

Appendix

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