Specific Heat Capacity

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Physics Coursework

Plan

Aim:

In this coursework, I aim to investigate the effect of density on the specific heat capacity of a metal. In order to do this I will carry out an experiment to find the specific heat capacity of each metal and I will then find the density of each.

Specific Heat Capacity:

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg the substance by 1oC, or by 1K. This can be found by calculation using the equation,

c = __Q__

     mΔT

where c is the specific heat capacity of the substance, Q is the energy given to, and used by the substance, m is its mass and ΔT is the temperature change.

Specific heat capacity, in elements, varies depending on the element due to the different molar masses of the different elements. Heat energy is as a result of the kinetic energy of the atoms or molecules in the substance, or the number of particles vibrating. As, at a given temperature, the average kinetic energy of atoms or molecules in any substance will be the same, specific heat capacity depends on the potential energy of the substance. If a substance has a lighter atomic mass, it has more potential energy as it will contain more atoms, or molecules, that are able to store heat energy. The energy ‘given’ to the substance is used to raise the internal energy of the substance and so if the substance has more potential energy, it will require more energy as the energy needs to change the potential energy of all of the molecules into kinetic energy to raise its temperature. Therefore, elements with lighter molar masses have higher specific heat capacities. This can be seen by the fact aluminium has a much greater specific heat capacity than many metals such as iron and copper, at 900Jkg-1K-1, as it has a much lighter molar mass.

Density:

The density of a substance is the mass of the substance divided by the volume of the substance. Mathematically it can be expressed as,

ρ = _m_

     V

where ρ is the density of the substance, m is its mass and v its volume. The density of an element depends on its relative atomic mass, as for an element of a certain volume, a certain number of atoms will be present, and as each atom will have a different mass to those of other element, the overall mass relative to volume will change.

Using this information, I predict that if density is increased, specific heat capacity will decrease. This is because if an element has a higher atomic mass, it will have a higher density due to the increased mass of each atom or molecule in the space available, and a lower specific heat capacity as it will have less potential energy that needs to be raised to increase the temperature.

Preliminary Experiment 1- Finding specific heat capacity using an electrical method.

In this experiment, I will test an electrical method for determining specific heat capacity to determine whether or not it is accurate enough to be used for my final experiment.

Apparatus require:

Cylinder of metal, approximately 1kg, with two holes drilled in (large enough to fit the heating element in one and a thermometer in the other)

Ammeter

Voltmeter

Stopwatch

Thermometer

Heating element

Power supply

Insulation (for example a felt casing for the metal cylinder)

Oil

Firstly, I found the precise mass of the metal being used. I then set up the apparatus as in the diagram above, placed some oil in the hole containing the heating element to minimise the lost through the air space, and recorded the starting temperature. Once the temperature had been recorded, I switched on the power supply and timed five minutes. During the five minutes I allowed the ammeter and voltmeter readings to settle and recorded the values. After the five minutes, I switched of the power supply and continually checked the thermometer until it had reached a maximum. I then recorded this value and repeated the experiment for each of the metals. I then repeated the experiment for each other metal.

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The results I obtain for each metal are shown in the table below:

These Values can be then be put into the formula

c = __Q__

        mΔT

to find the specific heat capacity of each metal as Q=ItV, where I is current (A0, V is voltage (V) and t is time (s)

Therefore, c =   ItV_  

                   mΔT

Using this equation I calculated the specific heat capacity of each metal as shown below:

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