Latent Heat of Fusion Essay

Abstract: A calorimeter, water at room temperature, ice, and a Pasco GLS Explorer were used in combination with a known value of the latent heat of fusion to create and carry out an experiment to determine the mass of an unknown amount of ice. Using the formula for latent heat of fusion, the mass of the ice was calculated to be 45.76g. The error of the carried out experiment was calculated to be 20.06%. Introduction:

A substance requires energy to change from one phase state to another, or in other words, when it goes from either a solid to liquid or liquid to gas.

The potential energy that is stored between molecules of the substance needs to be overcome by the kinetic energy of the motion of the particles before the substance can undergo the phase change. The temperature of a substance as heat is added to change the phase from the solid state to the gas state is shown below.

Phase changes are indicated by flat regions where heat energy is used to overcome attractive forces between molecules.

Starting a point A, the substance is in the solid state. Adding heat brings the temperature up until the substance reaches the melting point, but the material is still a solid at point B. As heat is further added, the energy from the heat source goes into breaking the bonds holding the atoms in place. At point C all of the solid phase has been transformed into the liquid phase. Once again, as energy is added the energy goes into the kinetic energy of the particles raising the temperature. At point D the temperature has reached the boiling point of the substance, but the still remain in the liquid state.

From points D to E thermal energy is overcoming the bonds, and the particles have enough kinetic energy to escape from the liquid state. The substance is entering the gas phase. Beyond E, further heating under pressure can raise the temperature still while the substance remains in the gas state. The energy required to change the phase of a substance is known as a latent heat; the word latent means hidden. When the substance transforms from the solid phase to the liquid phase, the latent heat of fusion must be used. And when the substance changes from the liquid state to the gas state, the latent heat of vaporization is used. The energy required, or latent heat is defined using the following equation: Q= m*L

where Q is energy, m is the mass of the substance that is undergoing the phase change, and L is the specific latent heat of fusion or vaporization. The specific latent heat of fusion measures the amount of heat energy required to change 1 kg of a solid into a liquid.

In this lab experiment, ice was added to pre-weighed, room temperature water in a calorimeter. As the ice melted, temperature of the system decreased. Heat was being added to the ice through the room temperature water. The minimum temperature of the ice water system was recorded. In accordance with the above mentioned equation, along with the known latent heat of fusion of water, a value of 80cal/g, or 334kJ/kg, and the amount of heat added, the mass of the ice could be determined. Purpose:

The purpose of this lab was to use a calorimeter, water at room temperature, ice, and a Pasco GLS Explorer in combination with a known value of the latent heat of fusion to create and carry out an experiment to determine the mass of an unknown amount of ice.

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